diff --git a/docs/shared_bindings_matrix.py b/docs/shared_bindings_matrix.py
index d5f838f75b..aa5ef02e28 100644
--- a/docs/shared_bindings_matrix.py
+++ b/docs/shared_bindings_matrix.py
@@ -98,7 +98,7 @@ def build_module_map():
     for module in modules:
         full_name = module
         search_name = module.lstrip("_")
-        re_pattern = "CIRCUITPY_{}\s=\s(.+)".format(search_name.upper())
+        re_pattern = "CIRCUITPY_{}\s*\??=\s*(.+)".format(search_name.upper())
         find_config = re.findall(re_pattern, configs)
         if not find_config:
             continue
diff --git a/locale/ID.po b/locale/ID.po
index ac10df5bf8..32053577c0 100644
--- a/locale/ID.po
+++ b/locale/ID.po
@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2020-04-27 18:34-0700\n"
+"POT-Creation-Date: 2020-05-04 19:52-0400\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language-Team: LANGUAGE <LL@li.org>\n"
@@ -1096,6 +1096,10 @@ msgstr "Tidak ada pin TX"
 msgid "No available clocks"
 msgstr ""
 
+#: shared-bindings/_bleio/PacketBuffer.c
+msgid "No connection: length cannot be determined"
+msgstr ""
+
 #: shared-bindings/board/__init__.c
 msgid "No default %q bus"
 msgstr "Tidak ada standar bus %q"
@@ -1445,6 +1449,10 @@ msgstr ""
 msgid "Too many displays"
 msgstr ""
 
+#: ports/nrf/common-hal/_bleio/PacketBuffer.c
+msgid "Total data to write is larger than outgoing_packet_length"
+msgstr ""
+
 #: py/obj.c
 msgid "Traceback (most recent call last):\n"
 msgstr ""
diff --git a/locale/circuitpython.pot b/locale/circuitpython.pot
index 4b18bfd478..aa465b0b72 100644
--- a/locale/circuitpython.pot
+++ b/locale/circuitpython.pot
@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2020-04-27 18:34-0700\n"
+"POT-Creation-Date: 2020-05-04 20:38-0400\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language-Team: LANGUAGE <LL@li.org>\n"
@@ -1085,6 +1085,10 @@ msgstr ""
 msgid "No available clocks"
 msgstr ""
 
+#: shared-bindings/_bleio/PacketBuffer.c
+msgid "No connection: length cannot be determined"
+msgstr ""
+
 #: shared-bindings/board/__init__.c
 msgid "No default %q bus"
 msgstr ""
@@ -1429,6 +1433,10 @@ msgstr ""
 msgid "Too many displays"
 msgstr ""
 
+#: ports/nrf/common-hal/_bleio/PacketBuffer.c
+msgid "Total data to write is larger than outgoing_packet_length"
+msgstr ""
+
 #: py/obj.c
 msgid "Traceback (most recent call last):\n"
 msgstr ""
diff --git a/locale/de_DE.po b/locale/de_DE.po
index 6cf4b7d479..7acebdb903 100644
--- a/locale/de_DE.po
+++ b/locale/de_DE.po
@@ -7,7 +7,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: \n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2020-04-27 18:34-0700\n"
+"POT-Creation-Date: 2020-05-04 19:52-0400\n"
 "PO-Revision-Date: 2018-07-27 11:55-0700\n"
 "Last-Translator: Pascal Deneaux\n"
 "Language-Team: Sebastian Plamauer, Pascal Deneaux\n"
@@ -1094,6 +1094,10 @@ msgstr "Kein TX Pin"
 msgid "No available clocks"
 msgstr "Keine Taktgeber verfügbar"
 
+#: shared-bindings/_bleio/PacketBuffer.c
+msgid "No connection: length cannot be determined"
+msgstr ""
+
 #: shared-bindings/board/__init__.c
 msgid "No default %q bus"
 msgstr "Kein Standard %q Bus"
@@ -1448,6 +1452,10 @@ msgstr ""
 msgid "Too many displays"
 msgstr "Zu viele displays"
 
+#: ports/nrf/common-hal/_bleio/PacketBuffer.c
+msgid "Total data to write is larger than outgoing_packet_length"
+msgstr ""
+
 #: py/obj.c
 msgid "Traceback (most recent call last):\n"
 msgstr "Zurückverfolgung (jüngste Aufforderung zuletzt):\n"
diff --git a/locale/en_US.po b/locale/en_US.po
index 428a9c4754..a3c2cd50e0 100644
--- a/locale/en_US.po
+++ b/locale/en_US.po
@@ -7,7 +7,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: \n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2020-04-27 18:34-0700\n"
+"POT-Creation-Date: 2020-05-04 19:52-0400\n"
 "PO-Revision-Date: 2018-07-27 11:55-0700\n"
 "Last-Translator: \n"
 "Language-Team: \n"
@@ -1085,6 +1085,10 @@ msgstr ""
 msgid "No available clocks"
 msgstr ""
 
+#: shared-bindings/_bleio/PacketBuffer.c
+msgid "No connection: length cannot be determined"
+msgstr ""
+
 #: shared-bindings/board/__init__.c
 msgid "No default %q bus"
 msgstr ""
@@ -1429,6 +1433,10 @@ msgstr ""
 msgid "Too many displays"
 msgstr ""
 
+#: ports/nrf/common-hal/_bleio/PacketBuffer.c
+msgid "Total data to write is larger than outgoing_packet_length"
+msgstr ""
+
 #: py/obj.c
 msgid "Traceback (most recent call last):\n"
 msgstr ""
diff --git a/locale/en_x_pirate.po b/locale/en_x_pirate.po
index aacc176f5c..86d217e3bc 100644
--- a/locale/en_x_pirate.po
+++ b/locale/en_x_pirate.po
@@ -7,7 +7,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: \n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2020-04-27 18:34-0700\n"
+"POT-Creation-Date: 2020-05-04 19:52-0400\n"
 "PO-Revision-Date: 2018-07-27 11:55-0700\n"
 "Last-Translator: \n"
 "Language-Team: @sommersoft, @MrCertainly\n"
@@ -1089,6 +1089,10 @@ msgstr ""
 msgid "No available clocks"
 msgstr ""
 
+#: shared-bindings/_bleio/PacketBuffer.c
+msgid "No connection: length cannot be determined"
+msgstr ""
+
 #: shared-bindings/board/__init__.c
 msgid "No default %q bus"
 msgstr ""
@@ -1433,6 +1437,10 @@ msgstr ""
 msgid "Too many displays"
 msgstr ""
 
+#: ports/nrf/common-hal/_bleio/PacketBuffer.c
+msgid "Total data to write is larger than outgoing_packet_length"
+msgstr ""
+
 #: py/obj.c
 msgid "Traceback (most recent call last):\n"
 msgstr ""
diff --git a/locale/es.po b/locale/es.po
index db60c9d37a..c3ff86454b 100644
--- a/locale/es.po
+++ b/locale/es.po
@@ -7,7 +7,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: \n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2020-04-27 18:34-0700\n"
+"POT-Creation-Date: 2020-05-04 19:52-0400\n"
 "PO-Revision-Date: 2018-08-24 22:56-0500\n"
 "Last-Translator: \n"
 "Language-Team: \n"
@@ -1093,6 +1093,10 @@ msgstr "Sin pin TX"
 msgid "No available clocks"
 msgstr "Relojes no disponibles"
 
+#: shared-bindings/_bleio/PacketBuffer.c
+msgid "No connection: length cannot be determined"
+msgstr ""
+
 #: shared-bindings/board/__init__.c
 msgid "No default %q bus"
 msgstr "Sin bus %q por defecto"
@@ -1446,6 +1450,10 @@ msgstr "Demasiados buses de pantalla"
 msgid "Too many displays"
 msgstr "Muchos displays"
 
+#: ports/nrf/common-hal/_bleio/PacketBuffer.c
+msgid "Total data to write is larger than outgoing_packet_length"
+msgstr ""
+
 #: py/obj.c
 msgid "Traceback (most recent call last):\n"
 msgstr "Traceback (ultima llamada reciente):\n"
diff --git a/locale/fil.po b/locale/fil.po
index 6d577823fa..11cba9d977 100644
--- a/locale/fil.po
+++ b/locale/fil.po
@@ -7,7 +7,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: \n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2020-04-27 18:34-0700\n"
+"POT-Creation-Date: 2020-05-04 19:52-0400\n"
 "PO-Revision-Date: 2018-12-20 22:15-0800\n"
 "Last-Translator: Timothy <me@timothygarcia.ca>\n"
 "Language-Team: fil\n"
@@ -1101,6 +1101,10 @@ msgstr "Walang TX pin"
 msgid "No available clocks"
 msgstr ""
 
+#: shared-bindings/_bleio/PacketBuffer.c
+msgid "No connection: length cannot be determined"
+msgstr ""
+
 #: shared-bindings/board/__init__.c
 msgid "No default %q bus"
 msgstr "Walang default na %q bus"
@@ -1452,6 +1456,10 @@ msgstr ""
 msgid "Too many displays"
 msgstr ""
 
+#: ports/nrf/common-hal/_bleio/PacketBuffer.c
+msgid "Total data to write is larger than outgoing_packet_length"
+msgstr ""
+
 #: py/obj.c
 msgid "Traceback (most recent call last):\n"
 msgstr "Traceback (pinakahuling huling tawag): \n"
diff --git a/locale/fr.po b/locale/fr.po
index 4d07eda19b..bcd20b5b48 100644
--- a/locale/fr.po
+++ b/locale/fr.po
@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: 0.1\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2020-04-27 18:34-0700\n"
+"POT-Creation-Date: 2020-05-04 19:52-0400\n"
 "PO-Revision-Date: 2019-04-14 20:05+0100\n"
 "Last-Translator: Pierrick Couturier <arofarn@arofarn.info>\n"
 "Language-Team: fr\n"
@@ -1108,6 +1108,10 @@ msgstr "Pas de broche TX"
 msgid "No available clocks"
 msgstr "Pas d'horloge disponible"
 
+#: shared-bindings/_bleio/PacketBuffer.c
+msgid "No connection: length cannot be determined"
+msgstr ""
+
 #: shared-bindings/board/__init__.c
 msgid "No default %q bus"
 msgstr "Pas de bus %q par défaut"
@@ -1467,6 +1471,10 @@ msgstr "Trop de bus d'affichage"
 msgid "Too many displays"
 msgstr "Trop d'affichages"
 
+#: ports/nrf/common-hal/_bleio/PacketBuffer.c
+msgid "Total data to write is larger than outgoing_packet_length"
+msgstr ""
+
 #: py/obj.c
 msgid "Traceback (most recent call last):\n"
 msgstr "Trace (appels les plus récents en dernier):\n"
diff --git a/locale/it_IT.po b/locale/it_IT.po
index 0c0825e5ec..3d67bf3280 100644
--- a/locale/it_IT.po
+++ b/locale/it_IT.po
@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2020-04-27 18:34-0700\n"
+"POT-Creation-Date: 2020-05-04 19:52-0400\n"
 "PO-Revision-Date: 2018-10-02 16:27+0200\n"
 "Last-Translator: Enrico Paganin <enrico.paganin@mail.com>\n"
 "Language-Team: \n"
@@ -1105,6 +1105,10 @@ msgstr "Nessun pin TX"
 msgid "No available clocks"
 msgstr "Nessun orologio a disposizione"
 
+#: shared-bindings/_bleio/PacketBuffer.c
+msgid "No connection: length cannot be determined"
+msgstr ""
+
 #: shared-bindings/board/__init__.c
 msgid "No default %q bus"
 msgstr "Nessun bus %q predefinito"
@@ -1463,6 +1467,10 @@ msgstr ""
 msgid "Too many displays"
 msgstr "Troppi schermi"
 
+#: ports/nrf/common-hal/_bleio/PacketBuffer.c
+msgid "Total data to write is larger than outgoing_packet_length"
+msgstr ""
+
 #: py/obj.c
 msgid "Traceback (most recent call last):\n"
 msgstr "Traceback (chiamata più recente per ultima):\n"
diff --git a/locale/ko.po b/locale/ko.po
index 3e3ac1cf60..4f87e51c9a 100644
--- a/locale/ko.po
+++ b/locale/ko.po
@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2020-04-27 18:34-0700\n"
+"POT-Creation-Date: 2020-05-04 19:52-0400\n"
 "PO-Revision-Date: 2019-05-06 14:22-0700\n"
 "Last-Translator: \n"
 "Language-Team: LANGUAGE <LL@li.org>\n"
@@ -1089,6 +1089,10 @@ msgstr ""
 msgid "No available clocks"
 msgstr ""
 
+#: shared-bindings/_bleio/PacketBuffer.c
+msgid "No connection: length cannot be determined"
+msgstr ""
+
 #: shared-bindings/board/__init__.c
 msgid "No default %q bus"
 msgstr ""
@@ -1433,6 +1437,10 @@ msgstr ""
 msgid "Too many displays"
 msgstr ""
 
+#: ports/nrf/common-hal/_bleio/PacketBuffer.c
+msgid "Total data to write is larger than outgoing_packet_length"
+msgstr ""
+
 #: py/obj.c
 msgid "Traceback (most recent call last):\n"
 msgstr ""
diff --git a/locale/pl.po b/locale/pl.po
index 8cc3c30b7a..cdf64cd038 100644
--- a/locale/pl.po
+++ b/locale/pl.po
@@ -7,7 +7,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: \n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2020-04-27 18:34-0700\n"
+"POT-Creation-Date: 2020-05-04 19:52-0400\n"
 "PO-Revision-Date: 2019-03-19 18:37-0700\n"
 "Last-Translator: Radomir Dopieralski <circuitpython@sheep.art.pl>\n"
 "Language-Team: pl\n"
@@ -1090,6 +1090,10 @@ msgstr "Brak nóżki TX"
 msgid "No available clocks"
 msgstr "Brak wolnych zegarów"
 
+#: shared-bindings/_bleio/PacketBuffer.c
+msgid "No connection: length cannot be determined"
+msgstr ""
+
 #: shared-bindings/board/__init__.c
 msgid "No default %q bus"
 msgstr "Nie ma domyślnej magistrali %q"
@@ -1434,6 +1438,10 @@ msgstr "Zbyt wiele magistrali"
 msgid "Too many displays"
 msgstr "Zbyt wiele wyświetlaczy"
 
+#: ports/nrf/common-hal/_bleio/PacketBuffer.c
+msgid "Total data to write is larger than outgoing_packet_length"
+msgstr ""
+
 #: py/obj.c
 msgid "Traceback (most recent call last):\n"
 msgstr "Ślad wyjątku (najnowsze wywołanie na końcu):\n"
diff --git a/locale/pt_BR.po b/locale/pt_BR.po
index d833169c0f..1398bb266f 100644
--- a/locale/pt_BR.po
+++ b/locale/pt_BR.po
@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2020-04-27 18:34-0700\n"
+"POT-Creation-Date: 2020-05-04 19:52-0400\n"
 "PO-Revision-Date: 2018-10-02 21:14-0000\n"
 "Last-Translator: \n"
 "Language-Team: \n"
@@ -1097,6 +1097,10 @@ msgstr "Nenhum pino TX"
 msgid "No available clocks"
 msgstr ""
 
+#: shared-bindings/_bleio/PacketBuffer.c
+msgid "No connection: length cannot be determined"
+msgstr ""
+
 #: shared-bindings/board/__init__.c
 msgid "No default %q bus"
 msgstr "Nenhum barramento %q padrão"
@@ -1446,6 +1450,10 @@ msgstr ""
 msgid "Too many displays"
 msgstr ""
 
+#: ports/nrf/common-hal/_bleio/PacketBuffer.c
+msgid "Total data to write is larger than outgoing_packet_length"
+msgstr ""
+
 #: py/obj.c
 msgid "Traceback (most recent call last):\n"
 msgstr ""
diff --git a/locale/sv.po b/locale/sv.po
index f993e52d32..d9beb3f551 100644
--- a/locale/sv.po
+++ b/locale/sv.po
@@ -8,7 +8,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: PACKAGE VERSION\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2020-04-27 18:34-0700\n"
+"POT-Creation-Date: 2020-05-04 20:38-0400\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language-Team: LANGUAGE <LL@li.org>\n"
@@ -1085,6 +1085,10 @@ msgstr ""
 msgid "No available clocks"
 msgstr ""
 
+#: shared-bindings/_bleio/PacketBuffer.c
+msgid "No connection: length cannot be determined"
+msgstr ""
+
 #: shared-bindings/board/__init__.c
 msgid "No default %q bus"
 msgstr ""
@@ -1429,6 +1433,10 @@ msgstr ""
 msgid "Too many displays"
 msgstr ""
 
+#: ports/nrf/common-hal/_bleio/PacketBuffer.c
+msgid "Total data to write is larger than outgoing_packet_length"
+msgstr ""
+
 #: py/obj.c
 msgid "Traceback (most recent call last):\n"
 msgstr ""
diff --git a/locale/zh_Latn_pinyin.po b/locale/zh_Latn_pinyin.po
index e7d6df02fa..b56cc3ce52 100644
--- a/locale/zh_Latn_pinyin.po
+++ b/locale/zh_Latn_pinyin.po
@@ -7,7 +7,7 @@ msgid ""
 msgstr ""
 "Project-Id-Version: circuitpython-cn\n"
 "Report-Msgid-Bugs-To: \n"
-"POT-Creation-Date: 2020-04-27 18:34-0700\n"
+"POT-Creation-Date: 2020-05-04 19:52-0400\n"
 "PO-Revision-Date: 2019-04-13 10:10-0700\n"
 "Last-Translator: hexthat\n"
 "Language-Team: Chinese Hanyu Pinyin\n"
@@ -1098,6 +1098,10 @@ msgstr "Wèi zhǎodào TX yǐn jiǎo"
 msgid "No available clocks"
 msgstr "Méiyǒu kěyòng de shízhōng"
 
+#: shared-bindings/_bleio/PacketBuffer.c
+msgid "No connection: length cannot be determined"
+msgstr ""
+
 #: shared-bindings/board/__init__.c
 msgid "No default %q bus"
 msgstr "wú mòrèn %q zǒngxiàn"
@@ -1455,6 +1459,10 @@ msgstr "Xiǎnshì zǒngxiàn tài duōle"
 msgid "Too many displays"
 msgstr "Xiǎnshì tài duō"
 
+#: ports/nrf/common-hal/_bleio/PacketBuffer.c
+msgid "Total data to write is larger than outgoing_packet_length"
+msgstr ""
+
 #: py/obj.c
 msgid "Traceback (most recent call last):\n"
 msgstr "Traceback (Zuìjìn yīcì dǎ diànhuà):\n"
diff --git a/ports/mimxrt10xx/common-hal/busio/UART.c b/ports/mimxrt10xx/common-hal/busio/UART.c
index 4633507d8b..e3642daf59 100644
--- a/ports/mimxrt10xx/common-hal/busio/UART.c
+++ b/ports/mimxrt10xx/common-hal/busio/UART.c
@@ -198,15 +198,18 @@ void common_hal_busio_uart_construct(busio_uart_obj_t *self,
       claim_pin(self->tx_pin->pin);
 
     if (self->rx_pin != NULL) {
-        ringbuf_alloc(&self->rbuf, receiver_buffer_size, true);
+        // The LPUART ring buffer wastes one byte to distinguish between full and empty.
+        self->ringbuf = gc_alloc(receiver_buffer_size + 1, false, true /*long-lived*/);
 
-        if (!self->rbuf.buf) {
+        if (!self->ringbuf) {
             LPUART_Deinit(self->uart);
             mp_raise_msg(&mp_type_MemoryError, translate("Failed to allocate RX buffer"));
         }
 
         LPUART_TransferCreateHandle(self->uart, &self->handle, LPUART_UserCallback, self);
-        LPUART_TransferStartRingBuffer(self->uart, &self->handle, self->rbuf.buf, self->rbuf.size);
+        // Pass actual allocated size; the LPUART routines are cognizant that
+        // the capacity is one less than the size.
+        LPUART_TransferStartRingBuffer(self->uart, &self->handle, self->ringbuf, receiver_buffer_size + 1);
 
         claim_pin(self->rx_pin->pin);
     }
@@ -223,9 +226,7 @@ void common_hal_busio_uart_deinit(busio_uart_obj_t *self) {
 
     LPUART_Deinit(self->uart);
 
-    gc_free(self->rbuf.buf);
-    self->rbuf.size = 0;
-    self->rbuf.iput = self->rbuf.iget = 0;
+    gc_free(self->ringbuf);
 
 //    reset_pin_number(self->rx_pin);
 //    reset_pin_number(self->tx_pin);
diff --git a/ports/mimxrt10xx/common-hal/busio/UART.h b/ports/mimxrt10xx/common-hal/busio/UART.h
index 9e768db3c0..3a326eb3a4 100644
--- a/ports/mimxrt10xx/common-hal/busio/UART.h
+++ b/ports/mimxrt10xx/common-hal/busio/UART.h
@@ -40,7 +40,7 @@ typedef struct {
     mp_obj_base_t base;
     LPUART_Type *uart;
     lpuart_handle_t handle;
-    ringbuf_t rbuf;
+    uint8_t* ringbuf;
     bool rx_ongoing;
     uint32_t baudrate;
     uint8_t character_bits;
diff --git a/ports/nrf/boards/circuitplayground_bluefruit/mpconfigboard.mk b/ports/nrf/boards/circuitplayground_bluefruit/mpconfigboard.mk
index f63554e5e8..38c9933340 100644
--- a/ports/nrf/boards/circuitplayground_bluefruit/mpconfigboard.mk
+++ b/ports/nrf/boards/circuitplayground_bluefruit/mpconfigboard.mk
@@ -11,7 +11,6 @@ EXTERNAL_FLASH_DEVICES = "GD25Q16C"
 
 # Allocate two, not just one I2C peripheral for CPB, so that we have both
 # on-board and off-board I2C available.
-# When SPIM3 becomes available we'll be able to have two I2C and two SPI peripherals.
 # We use a CFLAGS define here because there are include order issues
 # if we try to include "mpconfigport.h" into nrfx_config.h .
 CFLAGS += -DCIRCUITPY_NRF_NUM_I2C=2
diff --git a/ports/nrf/common-hal/_bleio/Characteristic.c b/ports/nrf/common-hal/_bleio/Characteristic.c
index e311aceb97..d507cecca4 100644
--- a/ports/nrf/common-hal/_bleio/Characteristic.c
+++ b/ports/nrf/common-hal/_bleio/Characteristic.c
@@ -127,6 +127,7 @@ size_t common_hal_bleio_characteristic_get_value(bleio_characteristic_obj_t *sel
             // self->value is set by evt handler.
             return common_hal_bleio_gattc_read(self->handle, conn_handle, buf, len);
         } else {
+            // conn_handle is ignored for non-system attributes.
             return common_hal_bleio_gatts_read(self->handle, conn_handle, buf, len);
         }
     }
@@ -152,6 +153,7 @@ void common_hal_bleio_characteristic_set_value(bleio_characteristic_obj_t *self,
                                          (self->props & CHAR_PROP_WRITE_NO_RESPONSE));
         } else {
             // Always write the value locally even if no connections are active.
+            // conn_handle is ignored for non-system attributes, so we use BLE_CONN_HANDLE_INVALID.
             common_hal_bleio_gatts_write(self->handle, BLE_CONN_HANDLE_INVALID, bufinfo);
             // Check to see if we need to notify or indicate any active connections.
             for (size_t i = 0; i < BLEIO_TOTAL_CONNECTION_COUNT; i++) {
diff --git a/ports/nrf/common-hal/_bleio/CharacteristicBuffer.c b/ports/nrf/common-hal/_bleio/CharacteristicBuffer.c
index c562d29e0e..132e392dd7 100644
--- a/ports/nrf/common-hal/_bleio/CharacteristicBuffer.c
+++ b/ports/nrf/common-hal/_bleio/CharacteristicBuffer.c
@@ -40,13 +40,11 @@
 #include "supervisor/shared/tick.h"
 #include "common-hal/_bleio/CharacteristicBuffer.h"
 
+// Push all the data onto the ring buffer. When the buffer is full, new bytes will be dropped.
 STATIC void write_to_ringbuf(bleio_characteristic_buffer_obj_t *self, uint8_t *data, uint16_t len) {
-    // Push all the data onto the ring buffer.
     uint8_t is_nested_critical_region;
     sd_nvic_critical_region_enter(&is_nested_critical_region);
-    for (size_t i = 0; i < len; i++) {
-        ringbuf_put(&self->ringbuf, data[i]);
-    }
+    ringbuf_put_n(&self->ringbuf, data, len);
     sd_nvic_critical_region_exit(is_nested_critical_region);
 }
 
@@ -98,11 +96,11 @@ void common_hal_bleio_characteristic_buffer_construct(bleio_characteristic_buffe
 
 }
 
-int common_hal_bleio_characteristic_buffer_read(bleio_characteristic_buffer_obj_t *self, uint8_t *data, size_t len, int *errcode) {
+uint32_t common_hal_bleio_characteristic_buffer_read(bleio_characteristic_buffer_obj_t *self, uint8_t *data, size_t len, int *errcode) {
     uint64_t start_ticks = supervisor_ticks_ms64();
 
     // Wait for all bytes received or timeout
-    while ( (ringbuf_count(&self->ringbuf) < len) && (supervisor_ticks_ms64() - start_ticks < self->timeout_ms) ) {
+    while ( (ringbuf_num_filled(&self->ringbuf) < len) && (supervisor_ticks_ms64() - start_ticks < self->timeout_ms) ) {
         RUN_BACKGROUND_TASKS;
         // Allow user to break out of a timeout with a KeyboardInterrupt.
         if ( mp_hal_is_interrupted() ) {
@@ -114,21 +112,18 @@ int common_hal_bleio_characteristic_buffer_read(bleio_characteristic_buffer_obj_
     uint8_t is_nested_critical_region;
     sd_nvic_critical_region_enter(&is_nested_critical_region);
 
-    size_t rx_bytes = MIN(ringbuf_count(&self->ringbuf), len);
-    for ( size_t i = 0; i < rx_bytes; i++ ) {
-        data[i] = ringbuf_get(&self->ringbuf);
-    }
+    uint32_t num_bytes_read = ringbuf_get_n(&self->ringbuf, data, len);
 
     // Writes now OK.
     sd_nvic_critical_region_exit(is_nested_critical_region);
 
-    return rx_bytes;
+    return num_bytes_read;
 }
 
 uint32_t common_hal_bleio_characteristic_buffer_rx_characters_available(bleio_characteristic_buffer_obj_t *self) {
     uint8_t is_nested_critical_region;
     sd_nvic_critical_region_enter(&is_nested_critical_region);
-    uint16_t count = ringbuf_count(&self->ringbuf);
+    uint16_t count = ringbuf_num_filled(&self->ringbuf);
     sd_nvic_critical_region_exit(is_nested_critical_region);
     return count;
 }
diff --git a/ports/nrf/common-hal/_bleio/Connection.c b/ports/nrf/common-hal/_bleio/Connection.c
index d4c7308fd1..00c1acd4d4 100644
--- a/ports/nrf/common-hal/_bleio/Connection.c
+++ b/ports/nrf/common-hal/_bleio/Connection.c
@@ -371,6 +371,11 @@ mp_float_t common_hal_bleio_connection_get_connection_interval(bleio_connection_
     return 1.25f * self->conn_params.min_conn_interval;
 }
 
+// Return the current negotiated MTU length, minus overhead.
+mp_int_t common_hal_bleio_connection_get_max_packet_length(bleio_connection_internal_t *self) {
+    return (self->mtu == 0 ? BLE_GATT_ATT_MTU_DEFAULT : self->mtu) - 3;
+}
+
 void common_hal_bleio_connection_set_connection_interval(bleio_connection_internal_t *self, mp_float_t new_interval) {
     self->conn_params_updating = true;
     uint16_t interval = new_interval / 1.25f;
@@ -752,3 +757,16 @@ mp_obj_t bleio_connection_new_from_internal(bleio_connection_internal_t* interna
 
     return MP_OBJ_FROM_PTR(connection);
 }
+
+// Find the connection that uses the given conn_handle. Return NULL if not found.
+bleio_connection_internal_t *bleio_conn_handle_to_connection(uint16_t conn_handle) {
+    bleio_connection_internal_t *connection;
+    for (size_t i = 0; i < BLEIO_TOTAL_CONNECTION_COUNT; i++) {
+        connection = &bleio_connections[i];
+        if (connection->conn_handle == conn_handle) {
+            return connection;
+        }
+    }
+
+    return NULL;
+}
diff --git a/ports/nrf/common-hal/_bleio/Connection.h b/ports/nrf/common-hal/_bleio/Connection.h
index 282e0c4b5d..b051e5c511 100644
--- a/ports/nrf/common-hal/_bleio/Connection.h
+++ b/ports/nrf/common-hal/_bleio/Connection.h
@@ -87,5 +87,6 @@ bool connection_on_ble_evt(ble_evt_t *ble_evt, void *self_in);
 
 uint16_t bleio_connection_get_conn_handle(bleio_connection_obj_t *self);
 mp_obj_t bleio_connection_new_from_internal(bleio_connection_internal_t* connection);
+bleio_connection_internal_t *bleio_conn_handle_to_connection(uint16_t conn_handle);
 
 #endif // MICROPY_INCLUDED_NRF_COMMON_HAL_BLEIO_CONNECTION_H
diff --git a/ports/nrf/common-hal/_bleio/PacketBuffer.c b/ports/nrf/common-hal/_bleio/PacketBuffer.c
index 6c360617f3..a8773f961f 100644
--- a/ports/nrf/common-hal/_bleio/PacketBuffer.c
+++ b/ports/nrf/common-hal/_bleio/PacketBuffer.c
@@ -41,7 +41,7 @@
 #include "supervisor/shared/tick.h"
 
 STATIC void write_to_ringbuf(bleio_packet_buffer_obj_t *self, uint8_t *data, uint16_t len) {
-    if (len + sizeof(uint16_t) > self->ringbuf.size) {
+    if (len + sizeof(uint16_t) > ringbuf_capacity(&self->ringbuf)) {
         // This shouldn't happen.
         return;
     }
@@ -49,7 +49,7 @@ STATIC void write_to_ringbuf(bleio_packet_buffer_obj_t *self, uint8_t *data, uin
     uint8_t is_nested_critical_region;
     sd_nvic_critical_region_enter(&is_nested_critical_region);
     // Make room for the new value by dropping the oldest packets first.
-    while (self->ringbuf.size - ringbuf_count(&self->ringbuf) < (int) (len + sizeof(uint16_t))) {
+    while (ringbuf_capacity(&self->ringbuf) - ringbuf_num_filled(&self->ringbuf) < len + sizeof(uint16_t)) {
         uint16_t packet_length;
         ringbuf_get_n(&self->ringbuf, (uint8_t*) &packet_length, sizeof(uint16_t));
         for (uint16_t i = 0; i < packet_length; i++) {
@@ -105,12 +105,18 @@ STATIC uint32_t queue_next_write(bleio_packet_buffer_obj_t *self) {
 }
 
 STATIC bool packet_buffer_on_ble_client_evt(ble_evt_t *ble_evt, void *param) {
-    bleio_packet_buffer_obj_t *self = (bleio_packet_buffer_obj_t *) param;
+    const uint16_t evt_id = ble_evt->header.evt_id;
+    // Check if this is a GATTC event so we can make sure the conn_handle is valid.
+    if (evt_id < BLE_GATTC_EVT_BASE || evt_id > BLE_GATTC_EVT_LAST) {
+        return false;
+    }
+
     uint16_t conn_handle = ble_evt->evt.gattc_evt.conn_handle;
+    bleio_packet_buffer_obj_t *self = (bleio_packet_buffer_obj_t *) param;
     if (conn_handle != self->conn_handle) {
         return false;
     }
-    switch (ble_evt->header.evt_id) {
+    switch (evt_id) {
         case BLE_GATTC_EVT_HVX: {
             // A remote service wrote to this characteristic.
             ble_gattc_evt_hvx_t* evt_hvx = &ble_evt->evt.gattc_evt.params.hvx;
@@ -140,9 +146,9 @@ STATIC bool packet_buffer_on_ble_client_evt(ble_evt_t *ble_evt, void *param) {
 
 STATIC bool packet_buffer_on_ble_server_evt(ble_evt_t *ble_evt, void *param) {
     bleio_packet_buffer_obj_t *self = (bleio_packet_buffer_obj_t *) param;
-    uint16_t conn_handle = ble_evt->evt.gatts_evt.conn_handle;
     switch (ble_evt->header.evt_id) {
         case BLE_GATTS_EVT_WRITE: {
+            uint16_t conn_handle = ble_evt->evt.gatts_evt.conn_handle;
             // A client wrote to this server characteristic.
 
             ble_gatts_evt_write_t *evt_write = &ble_evt->evt.gatts_evt.params.write;
@@ -166,7 +172,7 @@ STATIC bool packet_buffer_on_ble_server_evt(ble_evt_t *ble_evt, void *param) {
             break;
         }
         case BLE_GAP_EVT_DISCONNECTED: {
-            if (self->conn_handle == conn_handle) {
+            if (self->conn_handle == ble_evt->evt.gap_evt.conn_handle) {
                 self->conn_handle = BLE_CONN_HANDLE_INVALID;
             }
         }
@@ -200,10 +206,7 @@ void common_hal_bleio_packet_buffer_construct(
     }
 
     if (incoming) {
-        // This is a macro.
-        ringbuf_alloc(&self->ringbuf, buffer_size * (sizeof(uint16_t) + characteristic->max_length), false);
-
-        if (self->ringbuf.buf == NULL) {
+        if (!ringbuf_alloc(&self->ringbuf, buffer_size * (sizeof(uint16_t) + characteristic->max_length), false)) {
             mp_raise_ValueError(translate("Buffer too large and unable to allocate"));
         }
     }
@@ -247,45 +250,66 @@ void common_hal_bleio_packet_buffer_construct(
     }
 }
 
-int common_hal_bleio_packet_buffer_readinto(bleio_packet_buffer_obj_t *self, uint8_t *data, size_t len) {
-    if (ringbuf_count(&self->ringbuf) < 2) {
+mp_int_t common_hal_bleio_packet_buffer_readinto(bleio_packet_buffer_obj_t *self, uint8_t *data, size_t len) {
+    if (ringbuf_num_filled(&self->ringbuf) < 2) {
         return 0;
     }
 
-    uint16_t packet_length;
-    ringbuf_get_n(&self->ringbuf, (uint8_t*) &packet_length, sizeof(uint16_t));
-
     // Copy received data. Lock out write interrupt handler while copying.
     uint8_t is_nested_critical_region;
     sd_nvic_critical_region_enter(&is_nested_critical_region);
 
-    if (packet_length > len) {
-        return len - packet_length;
-    }
+    // Get packet length, which is in first two bytes of packet.
+    uint16_t packet_length;
+    ringbuf_get_n(&self->ringbuf, (uint8_t*) &packet_length, sizeof(uint16_t));
 
-    ringbuf_get_n(&self->ringbuf, data, packet_length);
+    mp_int_t ret;
+    if (packet_length > len) {
+        // Packet is longer than requested. Return negative of overrun value.
+        ret = len - packet_length;
+        // Discard the packet if it's too large. Don't fill data.
+        while (packet_length--) {
+            (void) ringbuf_get(&self->ringbuf);
+        }
+    } else {
+        // Read as much as possible, but might be shorter than len.
+        ringbuf_get_n(&self->ringbuf, data, packet_length);
+        ret = packet_length;
+    }
 
     // Writes now OK.
     sd_nvic_critical_region_exit(is_nested_critical_region);
 
-    return packet_length;
+    return ret;
 }
 
-void common_hal_bleio_packet_buffer_write(bleio_packet_buffer_obj_t *self, uint8_t *data, size_t len, uint8_t* header, size_t header_len) {
+mp_int_t common_hal_bleio_packet_buffer_write(bleio_packet_buffer_obj_t *self, uint8_t *data, size_t len, uint8_t* header, size_t header_len) {
     if (self->outgoing[0] == NULL) {
         mp_raise_bleio_BluetoothError(translate("Writes not supported on Characteristic"));
     }
     if (self->conn_handle == BLE_CONN_HANDLE_INVALID) {
-        return;
+        return -1;
     }
-    uint16_t packet_size = common_hal_bleio_packet_buffer_get_packet_size(self);
-    uint16_t max_size = packet_size - len;
-    while (max_size < self->pending_size && self->conn_handle != BLE_CONN_HANDLE_INVALID) {
-        RUN_BACKGROUND_TASKS;
+    uint16_t outgoing_packet_length = common_hal_bleio_packet_buffer_get_outgoing_packet_length(self);
+
+    if (len + header_len > outgoing_packet_length) {
+        // Supplied data will not fit in a single BLE packet.
+        mp_raise_ValueError(translate("Total data to write is larger than outgoing_packet_length"));
+    }
+
+    if (len + self->pending_size > outgoing_packet_length) {
+        // No room to append len bytes to packet. Wait until we get a free buffer,
+        // and keep checking that we haven't been disconnected.
+        while (self->pending_size != 0 && self->conn_handle != BLE_CONN_HANDLE_INVALID) {
+            RUN_BACKGROUND_TASKS;
+        }
     }
     if (self->conn_handle == BLE_CONN_HANDLE_INVALID) {
-        return;
+        return -1;
     }
+
+    size_t num_bytes_written = 0;
+
     uint8_t is_nested_critical_region;
     sd_nvic_critical_region_enter(&is_nested_critical_region);
 
@@ -294,9 +318,11 @@ void common_hal_bleio_packet_buffer_write(bleio_packet_buffer_obj_t *self, uint8
     if (self->pending_size == 0) {
         memcpy(pending, header, header_len);
         self->pending_size += header_len;
+        num_bytes_written += header_len;
     }
     memcpy(pending + self->pending_size, data, len);
     self->pending_size += len;
+    num_bytes_written += len;
 
     sd_nvic_critical_region_exit(is_nested_critical_region);
 
@@ -304,28 +330,69 @@ void common_hal_bleio_packet_buffer_write(bleio_packet_buffer_obj_t *self, uint8
     if (!self->packet_queued) {
         queue_next_write(self);
     }
+    return num_bytes_written;
 }
 
-uint16_t common_hal_bleio_packet_buffer_get_packet_size(bleio_packet_buffer_obj_t *self) {
-    uint16_t mtu;
-    if (self->conn_handle == BLE_CONN_HANDLE_INVALID) {
-        return 0;
+mp_int_t common_hal_bleio_packet_buffer_get_incoming_packet_length(bleio_packet_buffer_obj_t *self) {
+    // If this PacketBuffer is coming from a remote service via NOTIFY or INDICATE
+    // the maximum size is what can be sent in one
+    // BLE packet. But we must be connected to know that value.
+    //
+    // Otherwise it can be as long as the characteristic
+    // will permit, whether or not we're connected.
+
+    if (self->characteristic == NULL) {
+        return -1;
     }
-    bleio_connection_internal_t *connection;
-    for (size_t i = 0; i < BLEIO_TOTAL_CONNECTION_COUNT; i++) {
-        connection = &bleio_connections[i];
-        if (connection->conn_handle == self->conn_handle) {
-            break;
+
+    if (self->characteristic->service != NULL &&
+        self->characteristic->service->is_remote &&
+        (common_hal_bleio_characteristic_get_properties(self->characteristic) &
+         (CHAR_PROP_INDICATE | CHAR_PROP_NOTIFY))) {
+        // We are talking to a remote service, and data is arriving via NOTIFY or INDICATE.
+        if (self->conn_handle != BLE_CONN_HANDLE_INVALID) {
+            bleio_connection_internal_t *connection = bleio_conn_handle_to_connection(self->conn_handle);
+            if (connection) {
+                return MIN(common_hal_bleio_connection_get_max_packet_length(connection),
+                           self->characteristic->max_length);
+            }
         }
+        // There's no current connection, so we don't know the MTU, and
+        // we can't tell what the largest incoming packet length would be.
+        return -1;
     }
-    if (connection->mtu == 0) {
-        mtu = BLE_GATT_ATT_MTU_DEFAULT;
+    return self->characteristic->max_length;
+}
+
+mp_int_t common_hal_bleio_packet_buffer_get_outgoing_packet_length(bleio_packet_buffer_obj_t *self) {
+    // If we are sending data via NOTIFY or INDICATE, the maximum size
+    // is what can be sent in one BLE packet. But we must be connected
+    // to know that value.
+    //
+    // Otherwise it can be as long as the characteristic
+    // will permit, whether or not we're connected.
+
+    if (self->characteristic == NULL) {
+        return -1;
     }
-    if (self->characteristic->max_length > mtu) {
-        mtu = self->characteristic->max_length;
+
+    if (self->characteristic->service != NULL &&
+        !self->characteristic->service->is_remote &&
+        (common_hal_bleio_characteristic_get_properties(self->characteristic) &
+         (CHAR_PROP_INDICATE | CHAR_PROP_NOTIFY))) {
+        // We are sending to a client, via NOTIFY or INDICATE.
+        if (self->conn_handle != BLE_CONN_HANDLE_INVALID) {
+            bleio_connection_internal_t *connection = bleio_conn_handle_to_connection(self->conn_handle);
+            if (connection) {
+                return MIN(common_hal_bleio_connection_get_max_packet_length(connection),
+                           self->characteristic->max_length);
+            }
+        }
+        // There's no current connection, so we don't know the MTU, and
+        // we can't tell what the largest outgoing packet length would be.
+        return -1;
     }
-    uint16_t att_overhead = 3;
-    return mtu - att_overhead;
+    return self->characteristic->max_length;
 }
 
 bool common_hal_bleio_packet_buffer_deinited(bleio_packet_buffer_obj_t *self) {
diff --git a/ports/nrf/common-hal/_bleio/PacketBuffer.h b/ports/nrf/common-hal/_bleio/PacketBuffer.h
index cfccc852ed..699291749f 100644
--- a/ports/nrf/common-hal/_bleio/PacketBuffer.h
+++ b/ports/nrf/common-hal/_bleio/PacketBuffer.h
@@ -40,8 +40,10 @@ typedef struct {
     // Two outgoing buffers to alternate between. One will be queued for transmission by the SD and
     // the other is waiting to be queued and can be extended.
     uint8_t* outgoing[2];
-    uint16_t pending_size;
-    uint16_t conn_handle;
+    volatile uint16_t pending_size;
+    // We remember the conn_handle so we can do a NOTIFY/INDICATE to a client.
+    // We can find out the conn_handle on a Characteristic write or a CCCD write (but not a read).
+    volatile uint16_t conn_handle;
     uint8_t pending_index;
     uint8_t write_type;
     bool client;
diff --git a/ports/nrf/common-hal/_bleio/Service.h b/ports/nrf/common-hal/_bleio/Service.h
index f101bc825b..6ee9fe63de 100644
--- a/ports/nrf/common-hal/_bleio/Service.h
+++ b/ports/nrf/common-hal/_bleio/Service.h
@@ -39,6 +39,8 @@ typedef struct bleio_service_obj {
     bool is_remote;
     bool is_secondary;
     bleio_uuid_obj_t *uuid;
+    // The connection object is set only when this is a remote service.
+    // A local service doesn't know the connection.
     mp_obj_t connection;
     mp_obj_list_t *characteristic_list;
     // Range of attribute handles of this remote service.
diff --git a/ports/nrf/common-hal/_bleio/__init__.c b/ports/nrf/common-hal/_bleio/__init__.c
index 62a3a9299c..e84bba6626 100644
--- a/ports/nrf/common-hal/_bleio/__init__.c
+++ b/ports/nrf/common-hal/_bleio/__init__.c
@@ -118,8 +118,8 @@ void common_hal_bleio_check_connected(uint16_t conn_handle) {
 
 // GATTS read of a Characteristic or Descriptor.
 size_t common_hal_bleio_gatts_read(uint16_t handle, uint16_t conn_handle, uint8_t* buf, size_t len) {
-    // conn_handle might be BLE_CONN_HANDLE_INVALID if we're not connected, but that's OK, because
-    // we can still read and write the local value.
+    // conn_handle is ignored unless this is a system attribute.
+    // If we're not connected, that's OK, because we can still read and write the local value.
 
     ble_gatts_value_t gatts_value = {
         .p_value = buf,
@@ -132,8 +132,8 @@ size_t common_hal_bleio_gatts_read(uint16_t handle, uint16_t conn_handle, uint8_
 }
 
 void common_hal_bleio_gatts_write(uint16_t handle, uint16_t conn_handle, mp_buffer_info_t *bufinfo) {
-    // conn_handle might be BLE_CONN_HANDLE_INVALID if we're not connected, but that's OK, because
-    // we can still read and write the local value.
+    // conn_handle is ignored unless this is a system attribute.
+    // If we're not connected, that's OK, because we can still read and write the local value.
 
     ble_gatts_value_t gatts_value = {
         .p_value = bufinfo->buf,
diff --git a/ports/nrf/common-hal/busio/UART.c b/ports/nrf/common-hal/busio/UART.c
index 85626548f6..dbf40ea516 100644
--- a/ports/nrf/common-hal/busio/UART.c
+++ b/ports/nrf/common-hal/busio/UART.c
@@ -98,7 +98,7 @@ static void uart_callback_irq (const nrfx_uarte_event_t * event, void * context)
 
     switch ( event->type ) {
         case NRFX_UARTE_EVT_RX_DONE:
-            ringbuf_put_n(&self->rbuf, event->data.rxtx.p_data, event->data.rxtx.bytes);
+            ringbuf_put_n(&self->ringbuf, event->data.rxtx.p_data, event->data.rxtx.bytes);
 
             // keep receiving
             (void) nrfx_uarte_rx(self->uarte, &self->rx_char, 1);
@@ -112,7 +112,7 @@ static void uart_callback_irq (const nrfx_uarte_event_t * event, void * context)
             // Possible Error source is Overrun, Parity, Framing, Break
             // uint32_t errsrc = event->data.error.error_mask;
 
-            ringbuf_put_n(&self->rbuf, event->data.error.rxtx.p_data, event->data.error.rxtx.bytes);
+            ringbuf_put_n(&self->ringbuf, event->data.error.rxtx.p_data, event->data.error.rxtx.bytes);
 
             // Keep receiving
             (void) nrfx_uarte_rx(self->uarte, &self->rx_char, 1);
@@ -190,9 +190,7 @@ void common_hal_busio_uart_construct(busio_uart_obj_t *self,
         // pointers like this are NOT moved, allocating the buffer
         // in the long-lived pool is not strictly necessary)
         // (This is a macro.)
-        ringbuf_alloc(&self->rbuf, receiver_buffer_size, true);
-
-        if ( !self->rbuf.buf ) {
+        if (!ringbuf_alloc(&self->ringbuf, receiver_buffer_size, true)) {
             nrfx_uarte_uninit(self->uarte);
             mp_raise_msg(&mp_type_MemoryError, translate("Failed to allocate RX buffer"));
         }
@@ -226,10 +224,7 @@ void common_hal_busio_uart_deinit(busio_uart_obj_t *self) {
         reset_pin_number(self->rx_pin_number);
         self->tx_pin_number = NO_PIN;
         self->rx_pin_number = NO_PIN;
-
-        gc_free(self->rbuf.buf);
-        self->rbuf.size = 0;
-        self->rbuf.iput = self->rbuf.iget = 0;
+        ringbuf_free(&self->ringbuf);
     }
 }
 
@@ -239,11 +234,10 @@ size_t common_hal_busio_uart_read(busio_uart_obj_t *self, uint8_t *data, size_t
         mp_raise_ValueError(translate("No RX pin"));
     }
 
-    size_t rx_bytes = 0;
     uint64_t start_ticks = supervisor_ticks_ms64();
 
     // Wait for all bytes received or timeout
-    while ( (ringbuf_count(&self->rbuf) < len) && (supervisor_ticks_ms64() - start_ticks < self->timeout_ms) ) {
+    while ( (ringbuf_num_filled(&self->ringbuf) < len) && (supervisor_ticks_ms64() - start_ticks < self->timeout_ms) ) {
         RUN_BACKGROUND_TASKS;
         // Allow user to break out of a timeout with a KeyboardInterrupt.
         if ( mp_hal_is_interrupted() ) {
@@ -254,12 +248,8 @@ size_t common_hal_busio_uart_read(busio_uart_obj_t *self, uint8_t *data, size_t
     // prevent conflict with uart irq
     NVIC_DisableIRQ(nrfx_get_irq_number(self->uarte->p_reg));
 
-    // copy received data
-    rx_bytes = ringbuf_count(&self->rbuf);
-    rx_bytes = MIN(rx_bytes, len);
-    for ( uint16_t i = 0; i < rx_bytes; i++ ) {
-        data[i] = ringbuf_get(&self->rbuf);
-    }
+    // Copy as much received data as available, up to len bytes.
+    size_t rx_bytes = ringbuf_get_n(&self->ringbuf, data, len);
 
     NVIC_EnableIRQ(nrfx_get_irq_number(self->uarte->p_reg));
 
@@ -316,13 +306,13 @@ void common_hal_busio_uart_set_timeout(busio_uart_obj_t *self, mp_float_t timeou
 }
 
 uint32_t common_hal_busio_uart_rx_characters_available(busio_uart_obj_t *self) {
-    return ringbuf_count(&self->rbuf);
+    return ringbuf_num_filled(&self->ringbuf);
 }
 
 void common_hal_busio_uart_clear_rx_buffer(busio_uart_obj_t *self) {
     // prevent conflict with uart irq
     NVIC_DisableIRQ(nrfx_get_irq_number(self->uarte->p_reg));
-    ringbuf_clear(&self->rbuf);
+    ringbuf_clear(&self->ringbuf);
     NVIC_EnableIRQ(nrfx_get_irq_number(self->uarte->p_reg));
 }
 
diff --git a/ports/nrf/common-hal/busio/UART.h b/ports/nrf/common-hal/busio/UART.h
index 58432001cd..a251162910 100644
--- a/ports/nrf/common-hal/busio/UART.h
+++ b/ports/nrf/common-hal/busio/UART.h
@@ -41,7 +41,7 @@ typedef struct {
     uint32_t baudrate;
     uint32_t timeout_ms;
 
-    ringbuf_t rbuf;
+    ringbuf_t ringbuf;
     uint8_t rx_char; // EasyDMA buf
 
     uint8_t tx_pin_number;
diff --git a/ports/nrf/mpconfigport.mk b/ports/nrf/mpconfigport.mk
index 410d3750e5..58ab442823 100644
--- a/ports/nrf/mpconfigport.mk
+++ b/ports/nrf/mpconfigport.mk
@@ -14,39 +14,21 @@ USB_SERIAL_NUMBER_LENGTH = 16
 # All nRF ports have longints.
 LONGINT_IMPL = MPZ
 
+# The ?='s allow overriding in mpconfigboard.mk.
+
 # Audio via PWM
-ifndef CIRCUITPY_AUDIOCORE
-CIRCUITPY_AUDIOCORE = 1
-endif
-
 CIRCUITPY_AUDIOIO = 0
+CIRCUITPY_AUDIOBUSIO ?= 1
+CIRCUITPY_AUDIOCORE ?= 1
+CIRCUITPY_AUDIOMIXER ?= 1
+CIRCUITPY_AUDIOPWMIO ?= 1
 
-
-# The ifndef's allow overriding in mpconfigboard.mk.
-
-ifndef
-CIRCUITPY_BLEIO = 1
-endif
-
-ifndef CIRCUITPY_AUDIOMIXER
-CIRCUITPY_AUDIOMIXER = 1
-endif
-
-ifndef CIRCUITPY_AUDIOPWMIO
-CIRCUITPY_AUDIOPWMIO = 1
-endif
-
-ifndef CIRCUITPY_AUDIOBUSIO
-CIRCUITPY_AUDIOBUSIO = 1
-endif
+CIRCUITPY_BLEIO ?= 1
 
 # No I2CSlave implementation
 CIRCUITPY_I2CSLAVE = 0
 
-# enable RTC
-ifndef CIRCUITPY_RTC
-CIRCUITPY_RTC = 1
-endif
+CIRCUITPY_RTC ?= 1
 
 # frequencyio not yet implemented
 CIRCUITPY_FREQUENCYIO = 0
@@ -72,8 +54,6 @@ NRF_DEFINES += -DNRF52840_XXAA -DNRF52840
 # Defined here because system_nrf52840.c doesn't #include any of our own include files.
 CFLAGS += -DCONFIG_NFCT_PINS_AS_GPIOS
 
-CIRCUITPY_ULAB = 1
-
 else
 ifeq ($(MCU_CHIP),nrf52833)
 MCU_SERIES = m4
diff --git a/ports/stm/common-hal/busio/UART.c b/ports/stm/common-hal/busio/UART.c
index 76afa58484..54ac68d738 100644
--- a/ports/stm/common-hal/busio/UART.c
+++ b/ports/stm/common-hal/busio/UART.c
@@ -209,8 +209,7 @@ void common_hal_busio_uart_construct(busio_uart_obj_t *self,
 
     // Init buffer for rx and claim pins
     if (self->rx != NULL) {
-        ringbuf_alloc(&self->rbuf, receiver_buffer_size, true);
-        if (!self->rbuf.buf) {
+        if (!ringbuf_alloc(&self->ringbuf, receiver_buffer_size, true)) {
             mp_raise_ValueError(translate("UART Buffer allocation error"));
         }
         claim_pin(rx);
@@ -246,9 +245,7 @@ void common_hal_busio_uart_deinit(busio_uart_obj_t *self) {
     reset_pin_number(self->rx->pin->port,self->rx->pin->number);
     self->tx = NULL;
     self->rx = NULL;
-    gc_free(self->rbuf.buf);
-    self->rbuf.size = 0;
-    self->rbuf.iput = self->rbuf.iget = 0;
+    ringbuf_free(&self->ringbuf);
 }
 
 size_t common_hal_busio_uart_read(busio_uart_obj_t *self, uint8_t *data, size_t len, int *errcode) {
@@ -256,11 +253,10 @@ size_t common_hal_busio_uart_read(busio_uart_obj_t *self, uint8_t *data, size_t
         mp_raise_ValueError(translate("No RX pin"));
     }
 
-    size_t rx_bytes = 0;
     uint64_t start_ticks = supervisor_ticks_ms64();
 
     // Wait for all bytes received or timeout, same as nrf
-    while ( (ringbuf_count(&self->rbuf) < len) && (supervisor_ticks_ms64() - start_ticks < self->timeout_ms) ) {
+    while ( (ringbuf_num_filled(&self->ringbuf) < len) && (supervisor_ticks_ms64() - start_ticks < self->timeout_ms) ) {
         RUN_BACKGROUND_TASKS;
         //restart if it failed in the callback
         if (errflag != HAL_OK) {
@@ -274,12 +270,8 @@ size_t common_hal_busio_uart_read(busio_uart_obj_t *self, uint8_t *data, size_t
 
     // Halt reception
     HAL_NVIC_DisableIRQ(self->irq);
-    // copy received data
-    rx_bytes = ringbuf_count(&self->rbuf);
-    rx_bytes = MIN(rx_bytes, len);
-    for (uint16_t i = 0; i < rx_bytes; i++) {
-        data[i] = ringbuf_get(&self->rbuf);
-    }
+    // Copy as much received data as available, up to len bytes.
+    size_t rx_bytes = ringbuf_get_n(&self->ringbuf, data, len);
     HAL_NVIC_EnableIRQ(self->irq);
 
     if (rx_bytes == 0) {
@@ -319,7 +311,7 @@ void HAL_UART_RxCpltCallback(UART_HandleTypeDef *handle)
             if ((HAL_UART_GetState(handle) & HAL_UART_STATE_BUSY_RX) == HAL_UART_STATE_BUSY_RX) {
                 return;
             }
-            ringbuf_put_n(&context->rbuf, &context->rx_char, 1);
+            ringbuf_put_n(&context->ringbuf, &context->rx_char, 1);
             errflag = HAL_UART_Receive_IT(handle, &context->rx_char, 1);
 
             return;
@@ -378,13 +370,13 @@ void common_hal_busio_uart_set_timeout(busio_uart_obj_t *self, mp_float_t timeou
 }
 
 uint32_t common_hal_busio_uart_rx_characters_available(busio_uart_obj_t *self) {
-    return ringbuf_count(&self->rbuf);
+    return ringbuf_num_filled(&self->ringbuf);
 }
 
 void common_hal_busio_uart_clear_rx_buffer(busio_uart_obj_t *self) {
     // Halt reception
     HAL_NVIC_DisableIRQ(self->irq);
-    ringbuf_clear(&self->rbuf);
+    ringbuf_clear(&self->ringbuf);
     HAL_NVIC_EnableIRQ(self->irq);
 }
 
diff --git a/ports/stm/common-hal/busio/UART.h b/ports/stm/common-hal/busio/UART.h
index 5ac1d352ca..d1971ce27a 100644
--- a/ports/stm/common-hal/busio/UART.h
+++ b/ports/stm/common-hal/busio/UART.h
@@ -47,7 +47,7 @@ typedef struct {
     const mcu_periph_obj_t *tx;
     const mcu_periph_obj_t *rx;
 
-    ringbuf_t rbuf;
+    ringbuf_t ringbuf;
     uint8_t rx_char;
 
     uint32_t baudrate;
diff --git a/py/circuitpy_mpconfig.mk b/py/circuitpy_mpconfig.mk
index 30ab720d70..c0943230c6 100644
--- a/py/circuitpy_mpconfig.mk
+++ b/py/circuitpy_mpconfig.mk
@@ -27,37 +27,25 @@
 # Manually disable by overriding in #mpconfigboard.mk
 
 # Smaller builds can be forced for resource constrained chips (typically SAMD21s
-# without external flash) by setting CIRCUITPY_FULL_BUILD=0. Avoid using this 
+# without external flash) by setting CIRCUITPY_FULL_BUILD=0. Avoid using this
 # for merely incomplete ports, as it changes settings in other files.
-ifndef CIRCUITPY_FULL_BUILD
-    CIRCUITPY_FULL_BUILD = 1
-endif
+CIRCUITPY_FULL_BUILD ?= 1
 CFLAGS += -DCIRCUITPY_FULL_BUILD=$(CIRCUITPY_FULL_BUILD)
 
 
-ifndef CIRCUITPY_ANALOGIO
-CIRCUITPY_ANALOGIO = 1
-endif
+CIRCUITPY_ANALOGIO ?= 1
 CFLAGS += -DCIRCUITPY_ANALOGIO=$(CIRCUITPY_ANALOGIO)
 
-ifndef CIRCUITPY_AUDIOBUSIO
-CIRCUITPY_AUDIOBUSIO = $(CIRCUITPY_FULL_BUILD)
-endif
+CIRCUITPY_AUDIOBUSIO ?= $(CIRCUITPY_FULL_BUILD)
 CFLAGS += -DCIRCUITPY_AUDIOBUSIO=$(CIRCUITPY_AUDIOBUSIO)
 
-ifndef CIRCUITPY_AUDIOIO
-CIRCUITPY_AUDIOIO = $(CIRCUITPY_FULL_BUILD)
-endif
+CIRCUITPY_AUDIOIO ?= $(CIRCUITPY_FULL_BUILD)
 CFLAGS += -DCIRCUITPY_AUDIOIO=$(CIRCUITPY_AUDIOIO)
 
-ifndef CIRCUITPY_AUDIOIO_COMPAT
-CIRCUITPY_AUDIOIO_COMPAT = $(CIRCUITPY_AUDIOIO)
-endif
+CIRCUITPY_AUDIOIO_COMPAT ?= $(CIRCUITPY_AUDIOIO)
 CFLAGS += -DCIRCUITPY_AUDIOIO_COMPAT=$(CIRCUITPY_AUDIOIO_COMPAT)
 
-ifndef CIRCUITPY_AUDIOPWMIO
-CIRCUITPY_AUDIOPWMIO = 0
-endif
+CIRCUITPY_AUDIOPWMIO ?= 0
 CFLAGS += -DCIRCUITPY_AUDIOPWMIO=$(CIRCUITPY_AUDIOPWMIO)
 
 ifndef CIRCUITPY_AUDIOCORE
@@ -69,9 +57,7 @@ endif
 endif
 CFLAGS += -DCIRCUITPY_AUDIOCORE=$(CIRCUITPY_AUDIOCORE)
 
-ifndef CIRCUITPY_AUDIOMIXER
-CIRCUITPY_AUDIOMIXER = $(CIRCUITPY_AUDIOIO)
-endif
+CIRCUITPY_AUDIOMIXER ?= $(CIRCUITPY_AUDIOIO)
 CFLAGS += -DCIRCUITPY_AUDIOMIXER=$(CIRCUITPY_AUDIOMIXER)
 
 ifndef CIRCUITPY_AUDIOMP3
@@ -83,246 +69,156 @@ endif
 endif
 CFLAGS += -DCIRCUITPY_AUDIOMP3=$(CIRCUITPY_AUDIOMP3)
 
-ifndef CIRCUITPY_BITBANGIO
-CIRCUITPY_BITBANGIO = $(CIRCUITPY_FULL_BUILD)
-endif
+CIRCUITPY_BITBANGIO ?= $(CIRCUITPY_FULL_BUILD)
 CFLAGS += -DCIRCUITPY_BITBANGIO=$(CIRCUITPY_BITBANGIO)
 
 # Explicitly enabled for boards that support _bleio.
-ifndef CIRCUITPY_BLEIO
-CIRCUITPY_BLEIO = 0
-endif
+CIRCUITPY_BLEIO ?= 0
 CFLAGS += -DCIRCUITPY_BLEIO=$(CIRCUITPY_BLEIO)
 
-ifndef CIRCUITPY_BOARD
-CIRCUITPY_BOARD = 1
-endif
+CIRCUITPY_BOARD ?= 1
 CFLAGS += -DCIRCUITPY_BOARD=$(CIRCUITPY_BOARD)
 
-ifndef CIRCUITPY_BUSIO
-CIRCUITPY_BUSIO = 1
-endif
+CIRCUITPY_BUSIO ?= 1
 CFLAGS += -DCIRCUITPY_BUSIO=$(CIRCUITPY_BUSIO)
 
-ifndef CIRCUITPY_DIGITALIO
-CIRCUITPY_DIGITALIO = 1
-endif
+CIRCUITPY_DIGITALIO ?= 1
 CFLAGS += -DCIRCUITPY_DIGITALIO=$(CIRCUITPY_DIGITALIO)
 
-ifndef CIRCUITPY_DISPLAYIO
-CIRCUITPY_DISPLAYIO = $(CIRCUITPY_FULL_BUILD)
-endif
+CIRCUITPY_DISPLAYIO ?= $(CIRCUITPY_FULL_BUILD)
 CFLAGS += -DCIRCUITPY_DISPLAYIO=$(CIRCUITPY_DISPLAYIO)
 
-ifndef CIRCUITPY_FRAMEBUFFERIO
-CIRCUITPY_FRAMEBUFFERIO = 0
-endif
+CIRCUITPY_FRAMEBUFFERIO ?= 0
 CFLAGS += -DCIRCUITPY_FRAMEBUFFERIO=$(CIRCUITPY_FRAMEBUFFERIO)
 
-ifndef CIRCUITPY_FREQUENCYIO
-CIRCUITPY_FREQUENCYIO = $(CIRCUITPY_FULL_BUILD)
-endif
+CIRCUITPY_FREQUENCYIO ?= $(CIRCUITPY_FULL_BUILD)
 CFLAGS += -DCIRCUITPY_FREQUENCYIO=$(CIRCUITPY_FREQUENCYIO)
 
-ifndef CIRCUITPY_GAMEPAD
-CIRCUITPY_GAMEPAD = $(CIRCUITPY_FULL_BUILD)
-endif
+CIRCUITPY_GAMEPAD ?= $(CIRCUITPY_FULL_BUILD)
 CFLAGS += -DCIRCUITPY_GAMEPAD=$(CIRCUITPY_GAMEPAD)
 
-ifndef CIRCUITPY_GAMEPADSHIFT
-CIRCUITPY_GAMEPADSHIFT = 0
-endif
+CIRCUITPY_GAMEPADSHIFT ?= 0
 CFLAGS += -DCIRCUITPY_GAMEPADSHIFT=$(CIRCUITPY_GAMEPADSHIFT)
 
-ifndef CIRCUITPY_I2CSLAVE
-CIRCUITPY_I2CSLAVE = $(CIRCUITPY_FULL_BUILD)
-endif
+CIRCUITPY_I2CSLAVE ?= $(CIRCUITPY_FULL_BUILD)
 CFLAGS += -DCIRCUITPY_I2CSLAVE=$(CIRCUITPY_I2CSLAVE)
 
-ifndef CIRCUITPY_MATH
-CIRCUITPY_MATH = 1
-endif
+CIRCUITPY_MATH ?= 1
 CFLAGS += -DCIRCUITPY_MATH=$(CIRCUITPY_MATH)
 
-ifndef CIRCUITPY__EVE
-CIRCUITPY__EVE = 0
-endif
+CIRCUITPY__EVE ?= 0
 CFLAGS += -DCIRCUITPY__EVE=$(CIRCUITPY__EVE)
 
-ifndef CIRCUITPY_MICROCONTROLLER
-CIRCUITPY_MICROCONTROLLER = 1
-endif
+CIRCUITPY_MICROCONTROLLER ?= 1
 CFLAGS += -DCIRCUITPY_MICROCONTROLLER=$(CIRCUITPY_MICROCONTROLLER)
 
-ifndef CIRCUITPY_NEOPIXEL_WRITE
-CIRCUITPY_NEOPIXEL_WRITE = 1
-endif
+CIRCUITPY_NEOPIXEL_WRITE ?= 1
 CFLAGS += -DCIRCUITPY_NEOPIXEL_WRITE=$(CIRCUITPY_NEOPIXEL_WRITE)
 
 # Enabled on SAMD51. Won't fit on SAMD21 builds. Not tested on nRF or STM32F4 builds.
-ifndef CIRCUITPY_NETWORK
-CIRCUITPY_NETWORK = 0
-endif
+CIRCUITPY_NETWORK ?= 0
 CFLAGS += -DCIRCUITPY_NETWORK=$(CIRCUITPY_NETWORK)
 
-ifndef CIRCUITPY_NVM
-CIRCUITPY_NVM = 1
-endif
+CIRCUITPY_NVM ?= 1
 CFLAGS += -DCIRCUITPY_NVM=$(CIRCUITPY_NVM)
 
-ifndef CIRCUITPY_OS
-CIRCUITPY_OS = 1
-endif
+CIRCUITPY_OS ?= 1
 CFLAGS += -DCIRCUITPY_OS=$(CIRCUITPY_OS)
 
-ifndef CIRCUITPY_PIXELBUF
-CIRCUITPY_PIXELBUF = $(CIRCUITPY_FULL_BUILD)
-endif
+CIRCUITPY_PIXELBUF ?= $(CIRCUITPY_FULL_BUILD)
 CFLAGS += -DCIRCUITPY_PIXELBUF=$(CIRCUITPY_PIXELBUF)
 
 # Only for SAMD boards for the moment
-ifndef CIRCUITPY_RGBMATRIX
-CIRCUITPY_RGBMATRIX = 0
-endif
+CIRCUITPY_RGBMATRIX ?= 0
 CFLAGS += -DCIRCUITPY_RGBMATRIX=$(CIRCUITPY_RGBMATRIX)
 
-ifndef CIRCUITPY_PULSEIO
-CIRCUITPY_PULSEIO = 1
-endif
+CIRCUITPY_PULSEIO ?= 1
 CFLAGS += -DCIRCUITPY_PULSEIO=$(CIRCUITPY_PULSEIO)
 
 # Only for SAMD boards for the moment
-ifndef CIRCUITPY_PS2IO
-CIRCUITPY_PS2IO = 0
-endif
+CIRCUITPY_PS2IO ?= 0
 CFLAGS += -DCIRCUITPY_PS2IO=$(CIRCUITPY_PS2IO)
 
-ifndef CIRCUITPY_RANDOM
-CIRCUITPY_RANDOM = 1
-endif
+CIRCUITPY_RANDOM ?= 1
 CFLAGS += -DCIRCUITPY_RANDOM=$(CIRCUITPY_RANDOM)
 
-ifndef CIRCUITPY_ROTARYIO
-CIRCUITPY_ROTARYIO = 1
-endif
+CIRCUITPY_ROTARYIO ?= 1
 CFLAGS += -DCIRCUITPY_ROTARYIO=$(CIRCUITPY_ROTARYIO)
 
-ifndef CIRCUITPY_RTC
-CIRCUITPY_RTC = 1
-endif
+CIRCUITPY_RTC ?= 1
 CFLAGS += -DCIRCUITPY_RTC=$(CIRCUITPY_RTC)
 
 # CIRCUITPY_SAMD is handled in the atmel-samd tree.
 # Only for SAMD chips.
 # Assume not a SAMD build.
-ifndef CIRCUITPY_SAMD
-CIRCUITPY_SAMD = 0
-endif
+CIRCUITPY_SAMD ?= 0
 CFLAGS += -DCIRCUITPY_SAMD=$(CIRCUITPY_SAMD)
 
 # Currently always off.
-ifndef CIRCUITPY_STAGE
-CIRCUITPY_STAGE = 0
-endif
+CIRCUITPY_STAGE ?= 0
 CFLAGS += -DCIRCUITPY_STAGE=$(CIRCUITPY_STAGE)
 
-ifndef CIRCUITPY_STORAGE
-CIRCUITPY_STORAGE = 1
-endif
+CIRCUITPY_STORAGE ?= 1
 CFLAGS += -DCIRCUITPY_STORAGE=$(CIRCUITPY_STORAGE)
 
-ifndef CIRCUITPY_STRUCT
-CIRCUITPY_STRUCT = 1
-endif
+CIRCUITPY_STRUCT ?= 1
 CFLAGS += -DCIRCUITPY_STRUCT=$(CIRCUITPY_STRUCT)
 
-ifndef CIRCUITPY_SUPERVISOR
-CIRCUITPY_SUPERVISOR = 1
-endif
+CIRCUITPY_SUPERVISOR ?= 1
 CFLAGS += -DCIRCUITPY_SUPERVISOR=$(CIRCUITPY_SUPERVISOR)
 
-ifndef CIRCUITPY_TIME
-CIRCUITPY_TIME = 1
-endif
+CIRCUITPY_TIME ?= 1
 CFLAGS += -DCIRCUITPY_TIME=$(CIRCUITPY_TIME)
 
 # touchio might be native or generic. See circuitpy_defns.mk.
-ifndef CIRCUITPY_TOUCHIO_USE_NATIVE
-CIRCUITPY_TOUCHIO_USE_NATIVE = 0
-endif
+CIRCUITPY_TOUCHIO_USE_NATIVE ?= 0
 CFLAGS += -DCIRCUITPY_TOUCHIO_USE_NATIVE=$(CIRCUITPY_TOUCHIO_USE_NATIVE)
 
-ifndef CIRCUITPY_TOUCHIO
-CIRCUITPY_TOUCHIO = 1
-endif
+CIRCUITPY_TOUCHIO ?= 1
 CFLAGS += -DCIRCUITPY_TOUCHIO=$(CIRCUITPY_TOUCHIO)
 
 # For debugging.
-ifndef CIRCUITPY_UHEAP
-CIRCUITPY_UHEAP = 0
-endif
+CIRCUITPY_UHEAP ?= 0
 CFLAGS += -DCIRCUITPY_UHEAP=$(CIRCUITPY_UHEAP)
 
-ifndef CIRCUITPY_USB_HID
-CIRCUITPY_USB_HID = 1
-endif
+CIRCUITPY_USB_HID ?= 1
 CFLAGS += -DCIRCUITPY_USB_HID=$(CIRCUITPY_USB_HID)
 
-ifndef CIRCUITPY_USB_MIDI
-CIRCUITPY_USB_MIDI = 1
-endif
+CIRCUITPY_USB_MIDI ?= 1
 CFLAGS += -DCIRCUITPY_USB_MIDI=$(CIRCUITPY_USB_MIDI)
 
-ifndef CIRCUITPY_PEW
-CIRCUITPY_PEW = 0
-endif
+CIRCUITPY_PEW ?= 0
 CFLAGS += -DCIRCUITPY_PEW=$(CIRCUITPY_PEW)
 
 # For debugging.
-ifndef CIRCUITPY_USTACK
-CIRCUITPY_USTACK = 0
-endif
+CIRCUITPY_USTACK ?= 0
 CFLAGS += -DCIRCUITPY_USTACK=$(CIRCUITPY_USTACK)
 
 # Non-module conditionals
 
-ifndef CIRCUITPY_BITBANG_APA102
-CIRCUITPY_BITBANG_APA102 = 0
-endif
+CIRCUITPY_BITBANG_APA102 ?= 0
 CFLAGS += -DCIRCUITPY_BITBANG_APA102=$(CIRCUITPY_BITBANG_APA102)
 
 # Should busio.I2C() check for pullups?
 # Some boards in combination with certain peripherals may not want this.
-ifndef CIRCUITPY_REQUIRE_I2C_PULLUPS
-CIRCUITPY_REQUIRE_I2C_PULLUPS = 1
-endif
+CIRCUITPY_REQUIRE_I2C_PULLUPS ?= 1
 CFLAGS += -DCIRCUITPY_REQUIRE_I2C_PULLUPS=$(CIRCUITPY_REQUIRE_I2C_PULLUPS)
 
 # REPL over BLE
-ifndef CIRCUITPY_SERIAL_BLE
-CIRCUITPY_SERIAL_BLE = 0
-endif
+CIRCUITPY_SERIAL_BLE ?= 0
 CFLAGS += -DCIRCUITPY_SERIAL_BLE=$(CIRCUITPY_SERIAL_BLE)
 
-ifndef CIRCUITPY_BLE_FILE_SERVICE
-CIRCUITPY_BLE_FILE_SERVICE = 0
-endif
+CIRCUITPY_BLE_FILE_SERVICE ?= 0
 CFLAGS += -DCIRCUITPY_BLE_FILE_SERVICE=$(CIRCUITPY_BLE_FILE_SERVICE)
 
 # REPL over UART
-ifndef CIRCUITPY_SERIAL_UART
-CIRCUITPY_SERIAL_UART = 0
-endif
+CIRCUITPY_SERIAL_UART ?= 0
 CFLAGS += -DCIRCUITPY_SERIAL_UART=$(CIRCUITPY_SERIAL_UART)
 
 # ulab numerics library
-ifndef CIRCUITPY_ULAB
-CIRCUITPY_ULAB = $(CIRCUITPY_FULL_BUILD)
-endif
+CIRCUITPY_ULAB ?= $(CIRCUITPY_FULL_BUILD)
 CFLAGS += -DCIRCUITPY_ULAB=$(CIRCUITPY_ULAB)
 
 # Enabled micropython.native decorator (experimental)
-ifndef CIRCUITPY_ENABLE_MPY_NATIVE
-CIRCUITPY_ENABLE_MPY_NATIVE = 0
-endif
+CIRCUITPY_ENABLE_MPY_NATIVE ?= 0
 CFLAGS += -DCIRCUITPY_ENABLE_MPY_NATIVE=$(CIRCUITPY_ENABLE_MPY_NATIVE)
diff --git a/py/py.mk b/py/py.mk
index ec0625db68..a5c8a7dc65 100644
--- a/py/py.mk
+++ b/py/py.mk
@@ -258,6 +258,7 @@ PY_CORE_O_BASENAME = $(addprefix py/,\
 	repl.o \
 	smallint.o \
 	frozenmod.o \
+	ringbuf.o \
 	)
 
 PY_EXTMOD_O_BASENAME = \
diff --git a/py/ringbuf.c b/py/ringbuf.c
new file mode 100644
index 0000000000..c19f1d44bc
--- /dev/null
+++ b/py/ringbuf.c
@@ -0,0 +1,115 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2016 Paul Sokolovsky
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+ * THE SOFTWARE.
+ */
+
+#include "ringbuf.h"
+
+// Dynamic initialization. This should be accessible from a root pointer.
+// capacity is the number of bytes the ring buffer can hold. The actual
+// size of the buffer is one greater than that, due to how the buffer
+// handles empty and full statuses.
+bool ringbuf_alloc(ringbuf_t *r, size_t capacity, bool long_lived) {
+    r->buf = gc_alloc(capacity + 1, false, long_lived);
+    r->size = capacity +  1;
+    r->iget = r->iput = 0;
+    return r->buf != NULL;
+}
+
+void ringbuf_free(ringbuf_t *r) {
+    gc_free(r->buf);
+    r->size = 0;
+    ringbuf_clear(r);
+}
+
+size_t ringbuf_capacity(ringbuf_t *r) {
+    return r->size - 1;
+}
+
+// Returns -1 if buffer is empty, else returns byte fetched.
+int ringbuf_get(ringbuf_t *r) {
+    if (r->iget == r->iput) {
+        return -1;
+    }
+    uint8_t v = r->buf[r->iget++];
+    if (r->iget >= r->size) {
+        r->iget = 0;
+    }
+    return v;
+}
+
+// Returns -1 if no room in buffer, else returns 0.
+int ringbuf_put(ringbuf_t *r, uint8_t v) {
+    uint32_t iput_new = r->iput + 1;
+    if (iput_new >= r->size) {
+        iput_new = 0;
+    }
+    if (iput_new == r->iget) {
+        return -1;
+    }
+    r->buf[r->iput] = v;
+    r->iput = iput_new;
+    return 0;
+}
+
+void ringbuf_clear(ringbuf_t *r) {
+    r->iput = r->iget = 0;
+}
+
+// Number of free slots that can be written.
+size_t ringbuf_num_empty(ringbuf_t *r) {
+    return (r->size + r->iget - r->iput - 1) % r->size;
+}
+
+// Number of bytes available to read.
+size_t ringbuf_num_filled(ringbuf_t *r) {
+    return (r->size + r->iput - r->iget) % r->size;
+}
+
+// If the ring buffer fills up, not all bytes will be written.
+// Returns how many bytes were successfully written.
+size_t ringbuf_put_n(ringbuf_t* r, uint8_t* buf, size_t bufsize)
+{
+    for(size_t i=0; i < bufsize; i++) {
+        if ( ringbuf_put(r, buf[i]) < 0 ) {
+            // If ringbuf is full, give up and return how many bytes
+            // we wrote so far.
+            return i;
+        }
+    }
+    return bufsize;
+}
+
+// Returns how many bytes were fetched.
+size_t ringbuf_get_n(ringbuf_t* r, uint8_t* buf, size_t bufsize)
+{
+    for(size_t i=0; i < bufsize; i++) {
+        int b = ringbuf_get(r);
+        if (b < 0) {
+            return i;
+        }
+        buf[i] = b;
+    }
+    return bufsize;
+}
diff --git a/py/ringbuf.h b/py/ringbuf.h
index 7fc35d2661..476bd428f9 100644
--- a/py/ringbuf.h
+++ b/py/ringbuf.h
@@ -32,78 +32,27 @@
 
 typedef struct _ringbuf_t {
     uint8_t *buf;
-    uint16_t size;
-    uint16_t iget;
-    uint16_t iput;
+    // Allocated size; capacity is one less. Don't reference this directly.
+    uint32_t size;
+    uint32_t iget;
+    uint32_t iput;
 } ringbuf_t;
 
+// Note that the capacity of the buffer is N-1!
+
 // Static initialization:
 // byte buf_array[N];
 // ringbuf_t buf = {buf_array, sizeof(buf_array)};
 
-// Dynamic initialization. This creates root pointer!
-#define ringbuf_alloc(r, sz, long_lived)                   \
-{ \
-    (r)->buf = gc_alloc(sz, false, long_lived);   \
-    (r)->size = sz; \
-    (r)->iget = (r)->iput = 0; \
-}
+bool ringbuf_alloc(ringbuf_t *r, size_t capacity, bool long_lived);
+void ringbuf_free(ringbuf_t *r);
+size_t ringbuf_capacity(ringbuf_t *r);
+int ringbuf_get(ringbuf_t *r);
+int ringbuf_put(ringbuf_t *r, uint8_t v);
+void ringbuf_clear(ringbuf_t *r);
+size_t ringbuf_num_empty(ringbuf_t *r);
+size_t ringbuf_num_filled(ringbuf_t *r);
+size_t ringbuf_put_n(ringbuf_t* r, uint8_t* buf, size_t bufsize);
+size_t ringbuf_get_n(ringbuf_t* r, uint8_t* buf, size_t bufsize);
 
-static inline int ringbuf_get(ringbuf_t *r) {
-    if (r->iget == r->iput) {
-        return -1;
-    }
-    uint8_t v = r->buf[r->iget++];
-    if (r->iget >= r->size) {
-        r->iget = 0;
-    }
-    return v;
-}
-
-static inline int ringbuf_put(ringbuf_t *r, uint8_t v) {
-    uint32_t iput_new = r->iput + 1;
-    if (iput_new >= r->size) {
-        iput_new = 0;
-    }
-    if (iput_new == r->iget) {
-        return -1;
-    }
-    r->buf[r->iput] = v;
-    r->iput = iput_new;
-    return 0;
-}
-
-static inline uint16_t ringbuf_count(ringbuf_t *r)
-{
-    volatile int count = r->iput - r->iget;
-    if ( count < 0 ) {
-        count += r->size;
-    }
-
-    return (uint16_t) count;
-}
-
-static inline void ringbuf_clear(ringbuf_t *r)
-{
-    r->iput = r->iget = 0;
-}
-
-// will overwrite old data
-static inline void ringbuf_put_n(ringbuf_t* r, uint8_t* buf, uint8_t bufsize)
-{
-    for(uint8_t i=0; i < bufsize; i++) {
-        if ( ringbuf_put(r, buf[i]) < 0 ) {
-            // if full overwrite old data
-            (void) ringbuf_get(r);
-            ringbuf_put(r, buf[i]);
-        }
-    }
-}
-
-static inline void ringbuf_get_n(ringbuf_t* r, uint8_t* buf, uint8_t bufsize)
-{
-    for(uint8_t i=0; i < bufsize; i++) {
-        buf[i] = ringbuf_get(r);
-    }
-}
 #endif // MICROPY_INCLUDED_PY_RINGBUF_H
diff --git a/shared-bindings/_bleio/CharacteristicBuffer.h b/shared-bindings/_bleio/CharacteristicBuffer.h
index 83e6fef02f..e82e96ca96 100644
--- a/shared-bindings/_bleio/CharacteristicBuffer.h
+++ b/shared-bindings/_bleio/CharacteristicBuffer.h
@@ -32,7 +32,7 @@
 extern const mp_obj_type_t bleio_characteristic_buffer_type;
 
 extern void common_hal_bleio_characteristic_buffer_construct(bleio_characteristic_buffer_obj_t *self, bleio_characteristic_obj_t *characteristic, mp_float_t timeout, size_t buffer_size);
-int common_hal_bleio_characteristic_buffer_read(bleio_characteristic_buffer_obj_t *self, uint8_t *data, size_t len, int *errcode);
+uint32_t common_hal_bleio_characteristic_buffer_read(bleio_characteristic_buffer_obj_t *self, uint8_t *data, size_t len, int *errcode);
 uint32_t common_hal_bleio_characteristic_buffer_rx_characters_available(bleio_characteristic_buffer_obj_t *self);
 void common_hal_bleio_characteristic_buffer_clear_rx_buffer(bleio_characteristic_buffer_obj_t *self);
 bool common_hal_bleio_characteristic_buffer_deinited(bleio_characteristic_buffer_obj_t *self);
diff --git a/shared-bindings/_bleio/Connection.c b/shared-bindings/_bleio/Connection.c
index c157af3652..f612517bbf 100644
--- a/shared-bindings/_bleio/Connection.c
+++ b/shared-bindings/_bleio/Connection.c
@@ -214,6 +214,25 @@ STATIC mp_obj_t bleio_connection_get_connection_interval(mp_obj_t self_in) {
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_1(bleio_connection_get_connection_interval_obj, bleio_connection_get_connection_interval);
 
+//|   .. attribute:: max_packet_length
+//|
+//|     The maximum number of data bytes that can be sent in a single transmission,
+//|     not including overhead bytes.
+//|
+//|     This is the maximum number of bytes that can be sent in a notification,
+//|     which must be sent in a single packet.
+//|     But for a regular characteristic read or write, may be sent in multiple packets,
+//|     so this limit does not apply.
+//|
+STATIC mp_obj_t bleio_connection_get_max_packet_length(mp_obj_t self_in) {
+    bleio_connection_obj_t *self = MP_OBJ_TO_PTR(self_in);
+
+    bleio_connection_ensure_connected(self);
+    return mp_obj_new_int(common_hal_bleio_connection_get_max_packet_length(self->connection));
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(bleio_connection_get_max_packet_length_obj, bleio_connection_get_max_packet_length);
+
+
 STATIC mp_obj_t bleio_connection_set_connection_interval(mp_obj_t self_in, mp_obj_t interval_in) {
     bleio_connection_obj_t *self = MP_OBJ_TO_PTR(self_in);
 
@@ -233,6 +252,13 @@ const mp_obj_property_t bleio_connection_connection_interval_obj = {
                (mp_obj_t)&mp_const_none_obj },
 };
 
+const mp_obj_property_t bleio_connection_max_packet_length_obj = {
+    .base.type = &mp_type_property,
+    .proxy = { (mp_obj_t)&bleio_connection_get_max_packet_length_obj,
+               (mp_obj_t)&mp_const_none_obj,
+               (mp_obj_t)&mp_const_none_obj },
+};
+
 STATIC const mp_rom_map_elem_t bleio_connection_locals_dict_table[] = {
     // Methods
     { MP_ROM_QSTR(MP_QSTR_pair),                     MP_ROM_PTR(&bleio_connection_pair_obj) },
@@ -243,7 +269,7 @@ STATIC const mp_rom_map_elem_t bleio_connection_locals_dict_table[] = {
     { MP_ROM_QSTR(MP_QSTR_connected),           MP_ROM_PTR(&bleio_connection_connected_obj) },
     { MP_ROM_QSTR(MP_QSTR_paired),              MP_ROM_PTR(&bleio_connection_paired_obj) },
     { MP_ROM_QSTR(MP_QSTR_connection_interval), MP_ROM_PTR(&bleio_connection_connection_interval_obj) },
-
+    { MP_ROM_QSTR(MP_QSTR_max_packet_length),   MP_ROM_PTR(&bleio_connection_max_packet_length_obj) },
 };
 
 STATIC MP_DEFINE_CONST_DICT(bleio_connection_locals_dict, bleio_connection_locals_dict_table);
diff --git a/shared-bindings/_bleio/Connection.h b/shared-bindings/_bleio/Connection.h
index c6f2601608..a5313a9375 100644
--- a/shared-bindings/_bleio/Connection.h
+++ b/shared-bindings/_bleio/Connection.h
@@ -34,11 +34,12 @@
 
 extern const mp_obj_type_t bleio_connection_type;
 
-extern void common_hal_bleio_connection_pair(bleio_connection_internal_t *self, bool bond);
-extern void common_hal_bleio_connection_disconnect(bleio_connection_internal_t *self);
-extern bool common_hal_bleio_connection_get_connected(bleio_connection_obj_t *self);
-extern bool common_hal_bleio_connection_get_paired(bleio_connection_obj_t *self);
-extern mp_obj_tuple_t *common_hal_bleio_connection_discover_remote_services(bleio_connection_obj_t *self, mp_obj_t service_uuids_whitelist);
+void common_hal_bleio_connection_pair(bleio_connection_internal_t *self, bool bond);
+void common_hal_bleio_connection_disconnect(bleio_connection_internal_t *self);
+bool common_hal_bleio_connection_get_connected(bleio_connection_obj_t *self);
+mp_int_t common_hal_bleio_connection_get_max_packet_length(bleio_connection_internal_t *self);
+bool common_hal_bleio_connection_get_paired(bleio_connection_obj_t *self);
+mp_obj_tuple_t *common_hal_bleio_connection_discover_remote_services(bleio_connection_obj_t *self, mp_obj_t service_uuids_whitelist);
 
 mp_float_t common_hal_bleio_connection_get_connection_interval(bleio_connection_internal_t *self);
 void common_hal_bleio_connection_set_connection_interval(bleio_connection_internal_t *self, mp_float_t new_interval);
diff --git a/shared-bindings/_bleio/PacketBuffer.c b/shared-bindings/_bleio/PacketBuffer.c
index 9e3666044a..6dbf290729 100644
--- a/shared-bindings/_bleio/PacketBuffer.c
+++ b/shared-bindings/_bleio/PacketBuffer.c
@@ -42,8 +42,8 @@
 //|
 //| Accumulates a Characteristic's incoming packets in a FIFO buffer and facilitates packet aware
 //| outgoing writes. A packet's size is either the characteristic length or the maximum transmission
-//| unit (MTU), whichever is smaller. The MTU can change so check `packet_size` before creating a
-//| buffer to store data.
+//| unit (MTU) minus overhead, whichever is smaller. The MTU can change so check `incoming_packet_length`
+//| and `outgoing_packet_length` before creating a buffer to store data.
 //|
 //| When we're the server, we ignore all connections besides the first to subscribe to
 //| notifications.
@@ -51,7 +51,7 @@
 //| .. class:: PacketBuffer(characteristic, *, buffer_size)
 //|
 //|   Monitor the given Characteristic. Each time a new value is written to the Characteristic
-//|   add the newly-written bytes to a FIFO buffer.
+//|   add the newly-written packet of bytes to a FIFO buffer.
 //|
 //|   :param Characteristic characteristic: The Characteristic to monitor.
 //|     It may be a local Characteristic provided by a Peripheral Service, or a remote Characteristic
@@ -71,7 +71,7 @@ STATIC mp_obj_t bleio_packet_buffer_make_new(const mp_obj_type_t *type, size_t n
 
     const mp_obj_t characteristic = args[ARG_characteristic].u_obj;
 
-    const int buffer_size = args[ARG_buffer_size].u_int;
+    const mp_int_t buffer_size = args[ARG_buffer_size].u_int;
     if (buffer_size < 1) {
         mp_raise_ValueError_varg(translate("%q must be >= 1"), MP_QSTR_buffer_size);
     }
@@ -109,7 +109,7 @@ STATIC mp_obj_t bleio_packet_buffer_readinto(mp_obj_t self_in, mp_obj_t buffer_o
     mp_buffer_info_t bufinfo;
     mp_get_buffer_raise(buffer_obj, &bufinfo, MP_BUFFER_WRITE);
 
-    int size = common_hal_bleio_packet_buffer_readinto(self, bufinfo.buf, bufinfo.len);
+    mp_int_t size = common_hal_bleio_packet_buffer_readinto(self, bufinfo.buf, bufinfo.len);
     if (size < 0) {
         mp_raise_ValueError_varg(translate("Buffer too short by %d bytes"), size * -1);
     }
@@ -125,6 +125,9 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_2(bleio_packet_buffer_readinto_obj, bleio_packet_
 //|
 //|     This does not block until the data is sent. It only blocks until the data is pending.
 //|
+//|     :return: number of bytes written. May include header bytes when packet is empty.
+//|     :rtype: int
+//|
 // TODO: Add a kwarg `merge=False` to dictate whether subsequent writes are merged into a pending
 // one.
 STATIC mp_obj_t bleio_packet_buffer_write(mp_uint_t n_args, const mp_obj_t *pos_args, mp_map_t *kw_args) {
@@ -149,9 +152,21 @@ STATIC mp_obj_t bleio_packet_buffer_write(mp_uint_t n_args, const mp_obj_t *pos_
         mp_get_buffer_raise(args[ARG_header].u_obj, &header_bufinfo, MP_BUFFER_READ);
     }
 
-    common_hal_bleio_packet_buffer_write(self, data_bufinfo.buf, data_bufinfo.len,
-                                         header_bufinfo.buf, header_bufinfo.len);
-    return mp_const_none;
+    mp_int_t num_bytes_written = common_hal_bleio_packet_buffer_write(
+        self, data_bufinfo.buf, data_bufinfo.len, header_bufinfo.buf, header_bufinfo.len);
+    if (num_bytes_written < 0) {
+        // TODO: Raise an error if not connected. Right now the not-connected error
+        // is unreliable, because common_hal_bleio_packet_buffer_write()
+        // checks for conn_handle being set, but setting that
+        // can be delayed because conn_handle is discovered by spying on
+        // gatts write events, which may not have been sent yet.
+        //
+        // IDEAL:
+        // mp_raise_bleio_ConnectionError(translate("Not connected"));
+        // TEMPORARY:
+        num_bytes_written = 0;
+    }
+    return MP_OBJ_NEW_SMALL_INT(num_bytes_written);
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_KW(bleio_packet_buffer_write_obj, 1, bleio_packet_buffer_write);
 
@@ -168,31 +183,66 @@ STATIC MP_DEFINE_CONST_FUN_OBJ_1(bleio_packet_buffer_deinit_obj, bleio_packet_bu
 
 //|   .. attribute:: packet_size
 //|
-//|     Maximum size of each packet in bytes. This is the minimum of the Characteristic length and
-//|     the negotiated Maximum Transfer Unit (MTU).
+//|     `packet_size` is the same as `incoming_packet_length`.
+//|     The name `packet_size` is deprecated and
+//|     will be removed in CircuitPython 6.0.0.
 //|
-STATIC mp_obj_t bleio_packet_buffer_get_packet_size(mp_obj_t self_in) {
+//|   .. attribute:: incoming_packet_length
+//|
+//|     Maximum length in bytes of a packet we are reading.
+//|
+STATIC mp_obj_t bleio_packet_buffer_get_incoming_packet_length(mp_obj_t self_in) {
     bleio_packet_buffer_obj_t *self = MP_OBJ_TO_PTR(self_in);
 
-    return MP_OBJ_NEW_SMALL_INT(common_hal_bleio_packet_buffer_get_packet_size(self));
+    mp_int_t size = common_hal_bleio_packet_buffer_get_incoming_packet_length(self);
+    if (size < 0) {
+        mp_raise_ValueError(translate("No connection: length cannot be determined"));
+    }
+    return MP_OBJ_NEW_SMALL_INT(size);
 }
-STATIC MP_DEFINE_CONST_FUN_OBJ_1(bleio_packet_buffer_get_packet_size_obj, bleio_packet_buffer_get_packet_size);
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(bleio_packet_buffer_get_incoming_packet_length_obj, bleio_packet_buffer_get_incoming_packet_length);
 
-const mp_obj_property_t bleio_packet_buffer_packet_size_obj = {
+const mp_obj_property_t bleio_packet_buffer_incoming_packet_length_obj = {
     .base.type = &mp_type_property,
-    .proxy = { (mp_obj_t)&bleio_packet_buffer_get_packet_size_obj,
+    .proxy = { (mp_obj_t)&bleio_packet_buffer_get_incoming_packet_length_obj,
+               (mp_obj_t)&mp_const_none_obj,
+               (mp_obj_t)&mp_const_none_obj },
+};
+
+//|   .. attribute:: outgoing_packet_length
+//|
+//|     Maximum length in bytes of a packet we are writing.
+//|
+STATIC mp_obj_t bleio_packet_buffer_get_outgoing_packet_length(mp_obj_t self_in) {
+    bleio_packet_buffer_obj_t *self = MP_OBJ_TO_PTR(self_in);
+
+    mp_int_t size = common_hal_bleio_packet_buffer_get_outgoing_packet_length(self);
+    if (size < 0) {
+        mp_raise_ValueError(translate("No connection: length cannot be determined"));
+    }
+    return MP_OBJ_NEW_SMALL_INT(size);
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(bleio_packet_buffer_get_outgoing_packet_length_obj, bleio_packet_buffer_get_outgoing_packet_length);
+
+const mp_obj_property_t bleio_packet_buffer_outgoing_packet_length_obj = {
+    .base.type = &mp_type_property,
+    .proxy = { (mp_obj_t)&bleio_packet_buffer_get_outgoing_packet_length_obj,
                (mp_obj_t)&mp_const_none_obj,
                (mp_obj_t)&mp_const_none_obj },
 };
 
 STATIC const mp_rom_map_elem_t bleio_packet_buffer_locals_dict_table[] = {
-    { MP_ROM_QSTR(MP_QSTR_deinit),             MP_ROM_PTR(&bleio_packet_buffer_deinit_obj) },
+    { MP_ROM_QSTR(MP_QSTR_deinit),                     MP_ROM_PTR(&bleio_packet_buffer_deinit_obj) },
 
     // Standard stream methods.
-    { MP_OBJ_NEW_QSTR(MP_QSTR_readinto),       MP_ROM_PTR(&bleio_packet_buffer_readinto_obj) },
-    { MP_OBJ_NEW_QSTR(MP_QSTR_write),          MP_ROM_PTR(&bleio_packet_buffer_write_obj) },
+    { MP_OBJ_NEW_QSTR(MP_QSTR_readinto),               MP_ROM_PTR(&bleio_packet_buffer_readinto_obj) },
+    { MP_OBJ_NEW_QSTR(MP_QSTR_write),                  MP_ROM_PTR(&bleio_packet_buffer_write_obj) },
 
-    { MP_OBJ_NEW_QSTR(MP_QSTR_packet_size),    MP_ROM_PTR(&bleio_packet_buffer_packet_size_obj) },
+    // .packet_size is now an alias for .incoming_packet_length
+    // TODO: Remove in 6.0.0.
+    { MP_OBJ_NEW_QSTR(MP_QSTR_packet_size),            MP_ROM_PTR(&bleio_packet_buffer_incoming_packet_length_obj) },
+    { MP_OBJ_NEW_QSTR(MP_QSTR_incoming_packet_length), MP_ROM_PTR(&bleio_packet_buffer_incoming_packet_length_obj) },
+    { MP_OBJ_NEW_QSTR(MP_QSTR_outgoing_packet_length), MP_ROM_PTR(&bleio_packet_buffer_outgoing_packet_length_obj) },
 };
 
 STATIC MP_DEFINE_CONST_DICT(bleio_packet_buffer_locals_dict, bleio_packet_buffer_locals_dict_table);
diff --git a/shared-bindings/_bleio/PacketBuffer.h b/shared-bindings/_bleio/PacketBuffer.h
index 990a2f8bb0..769e0a0c78 100644
--- a/shared-bindings/_bleio/PacketBuffer.h
+++ b/shared-bindings/_bleio/PacketBuffer.h
@@ -34,9 +34,10 @@ extern const mp_obj_type_t bleio_packet_buffer_type;
 extern void common_hal_bleio_packet_buffer_construct(
     bleio_packet_buffer_obj_t *self, bleio_characteristic_obj_t *characteristic,
     size_t buffer_size);
-void common_hal_bleio_packet_buffer_write(bleio_packet_buffer_obj_t *self, uint8_t *data, size_t len, uint8_t* header, size_t header_len);
-int common_hal_bleio_packet_buffer_readinto(bleio_packet_buffer_obj_t *self, uint8_t *data, size_t len);
-uint16_t common_hal_bleio_packet_buffer_get_packet_size(bleio_packet_buffer_obj_t *self);
+mp_int_t common_hal_bleio_packet_buffer_write(bleio_packet_buffer_obj_t *self, uint8_t *data, size_t len, uint8_t* header, size_t header_len);
+mp_int_t common_hal_bleio_packet_buffer_readinto(bleio_packet_buffer_obj_t *self, uint8_t *data, size_t len);
+mp_int_t common_hal_bleio_packet_buffer_get_incoming_packet_length(bleio_packet_buffer_obj_t *self);
+mp_int_t common_hal_bleio_packet_buffer_get_outgoing_packet_length(bleio_packet_buffer_obj_t *self);
 bool common_hal_bleio_packet_buffer_deinited(bleio_packet_buffer_obj_t *self);
 void common_hal_bleio_packet_buffer_deinit(bleio_packet_buffer_obj_t *self);
 
diff --git a/shared-module/_bleio/ScanResults.c b/shared-module/_bleio/ScanResults.c
index 7ea0c165f4..ae36f8863d 100644
--- a/shared-module/_bleio/ScanResults.c
+++ b/shared-module/_bleio/ScanResults.c
@@ -45,10 +45,10 @@ bleio_scanresults_obj_t* shared_module_bleio_new_scanresults(size_t buffer_size,
 }
 
 mp_obj_t common_hal_bleio_scanresults_next(bleio_scanresults_obj_t *self) {
-    while (ringbuf_count(&self->buf) == 0 && !self->done && !mp_hal_is_interrupted()) {
+    while (ringbuf_num_filled(&self->buf) == 0 && !self->done && !mp_hal_is_interrupted()) {
         RUN_BACKGROUND_TASKS;
     }
-    if (ringbuf_count(&self->buf) == 0 || mp_hal_is_interrupted()) {
+    if (ringbuf_num_filled(&self->buf) == 0 || mp_hal_is_interrupted()) {
         return mp_const_none;
     }
 
@@ -97,7 +97,7 @@ void shared_module_bleio_scanresults_append(bleio_scanresults_obj_t* self,
                                             uint16_t len) {
     int32_t packet_size = sizeof(uint8_t) + sizeof(ticks_ms) + sizeof(rssi) + NUM_BLEIO_ADDRESS_BYTES +
         sizeof(addr_type) + sizeof(len) + len;
-    int32_t empty_space = self->buf.size - ringbuf_count(&self->buf);
+    int32_t empty_space = self->buf.size - ringbuf_num_filled(&self->buf);
     if (packet_size >= empty_space) {
         // We can't fit the packet so skip it.
         return;