diff --git a/ports/nrf/common-hal/_bleio/Adapter.c b/ports/nrf/common-hal/_bleio/Adapter.c
index 12d5090737..05cd0260b2 100644
--- a/ports/nrf/common-hal/_bleio/Adapter.c
+++ b/ports/nrf/common-hal/_bleio/Adapter.c
@@ -670,5 +670,4 @@ void bleio_adapter_reset(bleio_adapter_obj_t* adapter) {
         bleio_connection_internal_t *connection = &connections[i];
         connection->connection_obj = mp_const_none;
     }
-    bonding_reset();
 }
diff --git a/ports/nrf/common-hal/_bleio/Characteristic.c b/ports/nrf/common-hal/_bleio/Characteristic.c
index 81639898fc..a87cd6e186 100644
--- a/ports/nrf/common-hal/_bleio/Characteristic.c
+++ b/ports/nrf/common-hal/_bleio/Characteristic.c
@@ -133,7 +133,8 @@ void common_hal_bleio_characteristic_construct(bleio_characteristic_obj_t *self,
         common_hal_bleio_characteristic_set_value(self, initial_value_bufinfo);
     }
 
-    ble_drv_add_event_handler(characteristic_on_ble_evt, self);
+    self->handler_entry.next = NULL;
+////////////////    ble_drv_add_event_handler_entry(&self->handler_entry, characteristic_on_ble_evt, self);
 }
 
 bleio_descriptor_obj_t *common_hal_bleio_characteristic_get_descriptor_list(bleio_characteristic_obj_t *self) {
@@ -287,3 +288,8 @@ void common_hal_bleio_characteristic_set_cccd(bleio_characteristic_obj_t *self,
     }
 
 }
+
+void common_hal_bleio_characteristic_del(bleio_characteristic_obj_t *self) {
+    // Remove from event handler list, since the evt handler entry is built-in and not a heap object.
+    ble_drv_remove_event_handler(characteristic_on_ble_evt, self);
+}
diff --git a/ports/nrf/common-hal/_bleio/Characteristic.h b/ports/nrf/common-hal/_bleio/Characteristic.h
index bb8f28495e..5759321aa2 100644
--- a/ports/nrf/common-hal/_bleio/Characteristic.h
+++ b/ports/nrf/common-hal/_bleio/Characteristic.h
@@ -47,6 +47,7 @@ typedef struct _bleio_characteristic_obj {
     bleio_attribute_security_mode_t read_perm;
     bleio_attribute_security_mode_t write_perm;
     bleio_descriptor_obj_t *descriptor_list;
+    ble_drv_evt_handler_entry_t handler_entry;
     uint16_t user_desc_handle;
     uint16_t cccd_handle;
     uint16_t sccd_handle;
diff --git a/ports/nrf/common-hal/_bleio/__init__.c b/ports/nrf/common-hal/_bleio/__init__.c
index 4b2780dedc..b9fbaa7c33 100644
--- a/ports/nrf/common-hal/_bleio/__init__.c
+++ b/ports/nrf/common-hal/_bleio/__init__.c
@@ -94,6 +94,7 @@ void bleio_reset() {
         common_hal_bleio_adapter_set_enabled(&common_hal_bleio_adapter_obj, false);
     }
     supervisor_start_bluetooth();
+    bonding_reset();
 }
 
 // The singleton _bleio.Adapter object, bound to _bleio.adapter
diff --git a/ports/nrf/common-hal/_bleio/bonding.c b/ports/nrf/common-hal/_bleio/bonding.c
index 1675ade43d..1175f72e47 100644
--- a/ports/nrf/common-hal/_bleio/bonding.c
+++ b/ports/nrf/common-hal/_bleio/bonding.c
@@ -34,7 +34,7 @@
 #include "shared-bindings/_bleio/Adapter.h"
 #include "shared-bindings/nvm/ByteArray.h"
 
-#include "nrf_nvmc.h"
+#include "nrf_soc.h"
 #include "sd_mutex.h"
 
 #include "bonding.h"
@@ -68,15 +68,17 @@ STATIC inline size_t compute_block_size(uint16_t data_length) {
 
 STATIC void erase_bonding_storage(void) {
     // Erase all pages in the bonding area.
-    BONDING_DEBUG_PRINTF("erase_bonding_storage()\n");
     for(uint32_t page_address = BONDING_PAGES_START_ADDR;
         page_address < BONDING_PAGES_END_ADDR;
         page_address += FLASH_PAGE_SIZE) {
-        nrf_nvmc_page_erase(page_address);
+        // Argument is page number, not address.
+        sd_flash_page_erase_sync(page_address / FLASH_PAGE_SIZE);
     }
     // Write marker words at the beginning and the end of the bonding area.
-    nrf_nvmc_write_word(BONDING_DATA_START_ADDR, BONDING_START_FLAG_ADDR);
-    nrf_nvmc_write_word(BONDING_DATA_END_ADDR, BONDING_END_FLAG_ADDR);
+    uint32_t flag = BONDING_START_FLAG;
+    sd_flash_write_sync((uint32_t *) BONDING_DATA_START_ADDR, &flag, 1);
+    flag = BONDING_END_FLAG;
+    sd_flash_write_sync((uint32_t *) BONDING_DATA_END_ADDR, &flag, 1);
     // First unused block is at the beginning.
     bonding_unused_block = (bonding_block_t *) BONDING_DATA_START_ADDR;
 }
@@ -135,7 +137,8 @@ STATIC bonding_block_t *find_block(bool is_central, bonding_block_type_t type, u
 // We don't change data_length, so we can still skip over this block.
 STATIC void invalidate_block(bonding_block_t *block) {
     BONDING_DEBUG_PRINTF("invalidate_block()\n");
-    nrf_nvmc_write_word((uint32_t) block, 0x00000000);
+    uint32_t zero = 0;
+    sd_flash_write_sync((uint32_t *) block, &zero, 1);
 }
 
 STATIC void queue_write_block(bool is_central, bonding_block_type_t type, uint16_t ediv, uint16_t conn_handle, uint8_t *data, uint16_t data_length) {
@@ -178,7 +181,7 @@ STATIC void write_block_header(bonding_block_t *block) {
         erase_bonding_storage();
     }
 
-    nrf_nvmc_write_words((uint32_t) bonding_unused_block, (uint32_t *) block, sizeof(bonding_block_t) / 4);
+    sd_flash_write_sync((uint32_t *) bonding_unused_block, (uint32_t *) block, sizeof(bonding_block_t) / 4);
 }
 
 // Write variable-length data at end of bonding block.
@@ -190,7 +193,7 @@ STATIC void write_block_data(uint8_t *data, uint16_t data_length) {
     while (1) {
         uint32_t word = 0xffffffff;
         memcpy(&word, data, data_length >= 4 ? 4 : data_length);
-        nrf_nvmc_write_word((uint32_t) flash_word_p, word);
+        sd_flash_write_sync(flash_word_p, &word, 1);
         if (data_length <= 4) {
             break;
         }
@@ -242,8 +245,9 @@ void bonding_clear_keys(bonding_keys_t *bonding_keys) {
     memset((uint8_t*) bonding_keys, 0, sizeof(bonding_keys_t));
 }
 
+// Call only when SD is enabled.
 void bonding_reset(void) {
-    BONDING_DEBUG_PRINTF("bonding_reset()\n");
+    MP_STATE_VM(queued_bonding_block_list) = NULL;
     sd_mutex_new(&queued_bonding_block_list_mutex);
     if (BONDING_START_FLAG != *((uint32_t *) BONDING_START_FLAG_ADDR) ||
         BONDING_END_FLAG != *((uint32_t *) BONDING_END_FLAG_ADDR)) {
@@ -256,18 +260,20 @@ void bonding_reset(void) {
 // Write bonding blocks to flash. These have been queued during event handlers.
 // We do one at a time, on each background call.
 void bonding_background(void) {
-
+    uint8_t sd_en = 0;
+    (void) sd_softdevice_is_enabled(&sd_en);
+    if (!sd_en) {
+        return;
+    }
     // Get block at front of list.
     sd_mutex_acquire_wait(&queued_bonding_block_list_mutex);
-    bonding_block_t *block = &(MP_STATE_VM(queued_bonding_block_list)->bonding_block);
+    bonding_block_t *block = (bonding_block_t *) MP_STATE_VM(queued_bonding_block_list);
     if (block) {
-        // Remove written block from front of list.
+        // Remove block from list.
         MP_STATE_VM(queued_bonding_block_list) = MP_STATE_VM(queued_bonding_block_list)->next_queued_block;
     }
     sd_mutex_release(&queued_bonding_block_list_mutex);
-
     if (!block) {
-        // No blocks in queue.
         return;
     }
 
diff --git a/ports/nrf/peripherals/nrf/nvm.c b/ports/nrf/peripherals/nrf/nvm.c
index d13775d4dd..2417ec66a9 100644
--- a/ports/nrf/peripherals/nrf/nvm.c
+++ b/ports/nrf/peripherals/nrf/nvm.c
@@ -38,29 +38,62 @@
 #include "ble_drv.h"
 #include "nrf_sdm.h"
 
+STATIC bool sd_is_enabled(void) {
+    uint8_t sd_en = 0;
+    (void) sd_softdevice_is_enabled(&sd_en);
+    return sd_en;
+}
+
 STATIC void sd_flash_operation_start(void) {
     sd_flash_operation_status = SD_FLASH_OPERATION_IN_PROGRESS;
 }
 
 STATIC sd_flash_operation_status_t sd_flash_operation_wait_until_done(void) {
-    while (sd_flash_operation_status == SD_FLASH_OPERATION_IN_PROGRESS) {
-        sd_app_evt_wait();
+    // If the SD is not enabled, no events are generated, so just return immediately.
+    if (sd_is_enabled()) {
+        while (sd_flash_operation_status == SD_FLASH_OPERATION_IN_PROGRESS) {
+            sd_app_evt_wait();
+        }
+    } else {
+        sd_flash_operation_status = SD_FLASH_OPERATION_DONE;
     }
     return sd_flash_operation_status;
+
 }
+
+bool sd_flash_page_erase_sync(uint32_t page_number) {
+    sd_flash_operation_start();
+    if (sd_flash_page_erase(page_number) != NRF_SUCCESS) {
+        return false;
+    }
+    if (sd_flash_operation_wait_until_done() == SD_FLASH_OPERATION_ERROR) {
+        return false;
+    }
+    return true;
+}
+
+bool sd_flash_write_sync(uint32_t *dest_words, uint32_t* src_words, uint32_t num_words) {
+    sd_flash_operation_start();
+    if (sd_flash_write(dest_words, src_words, num_words) != NRF_SUCCESS) {
+        return false;
+    }
+    if (sd_flash_operation_wait_until_done() == SD_FLASH_OPERATION_ERROR) {
+        return false;
+    }
+    return true;
+}
+
 #endif
 
 // The nRF52840 datasheet specifies a maximum of two writes to a flash
 // location before an erase is necessary, even if the write is all
 // ones (erased state).  So we can't avoid erases even if the page
 // appears to be already erased (all ones), unless we keep track of
-// writes to a page.
+// writes to a page.g
 
 bool nrf_nvm_safe_flash_page_write(uint32_t page_addr, uint8_t *data) {
     #ifdef BLUETOOTH_SD
-        uint8_t sd_en = 0;
-        (void) sd_softdevice_is_enabled(&sd_en);
-        if (sd_en) {
+        if (sd_is_enabled()) {
             uint32_t err_code;
             sd_flash_operation_status_t status;
 
diff --git a/ports/nrf/peripherals/nrf/nvm.h b/ports/nrf/peripherals/nrf/nvm.h
index e54e953dfc..8ba95773d6 100644
--- a/ports/nrf/peripherals/nrf/nvm.h
+++ b/ports/nrf/peripherals/nrf/nvm.h
@@ -27,4 +27,9 @@
 
 #define FLASH_PAGE_SIZE (4096)
 
+#if BLUETOOTH_SD
+bool sd_flash_page_erase_sync(uint32_t page_number);
+bool sd_flash_write_sync(uint32_t *dest_words, uint32_t* src_words, uint32_t num_words);
+#endif
+
 bool nrf_nvm_safe_flash_page_write(uint32_t page_addr, uint8_t *data);
diff --git a/ports/nrf/sd.c b/ports/nrf/sd.c
new file mode 100644
index 0000000000..b3162e6af9
--- /dev/null
+++ b/ports/nrf/sd.c
@@ -0,0 +1,54 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2019 Dan Halbert for Adafruit Industries
+ *
+ * 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 "py/mpconfig.h"
+#include "py/runtime.h"
+#include "nrf_soc.h"
+
+void sd_mutex_acquire_check(nrf_mutex_t* p_mutex) {
+    uint32_t err_code = sd_mutex_acquire(p_mutex);
+    if (err_code != NRF_SUCCESS) {
+        mp_raise_OSError_msg_varg(translate("Failed to acquire mutex, err 0x%04x"), err_code);
+    }
+}
+
+void sd_mutex_acquire_wait(nrf_mutex_t* p_mutex) {
+    while (sd_mutex_acquire(p_mutex) == NRF_ERROR_SOC_MUTEX_ALREADY_TAKEN) {
+        RUN_BACKGROUND_TASKS;
+    }
+}
+
+void sd_mutex_acquire_wait_no_vm(nrf_mutex_t* p_mutex) {
+    while (sd_mutex_acquire(p_mutex) == NRF_ERROR_SOC_MUTEX_ALREADY_TAKEN) {
+    }
+}
+
+void sd_mutex_release_check(nrf_mutex_t* p_mutex) {
+    uint32_t err_code = sd_mutex_release(p_mutex);
+    if (err_code != NRF_SUCCESS) {
+        mp_raise_OSError_msg_varg(translate("Failed to release mutex, err 0x%04x"), err_code);
+    }
+}
diff --git a/ports/nrf/sd.h b/ports/nrf/sd.h
new file mode 100644
index 0000000000..ca46917205
--- /dev/null
+++ b/ports/nrf/sd.h
@@ -0,0 +1,46 @@
+/*
+ * This file is part of the MicroPython project, http://micropython.org/
+ *
+ * The MIT License (MIT)
+ *
+ * Copyright (c) 2019 Dan Halbert for Adafruit Industries
+ *
+ * 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.
+ */
+
+#ifndef MICROPY_INCLUDED_NRF_SD_MUTEX_H
+#define MICROPY_INCLUDED_NRF_SD_MUTEX_H
+
+#include "nrf_soc.h"
+
+// Helpers for common usage of nrf_mutex.
+
+// Try to acquire a mutex right now. Raise exception if we can't get it.
+void sd_mutex_acquire_check(nrf_mutex_t* p_mutex);
+
+// Wait for a mutex to become available. Run VM background tasks while waiting.
+void sd_mutex_acquire_wait(nrf_mutex_t* p_mutex);
+
+// Wait for a mutex to become available.. Block VM while waiting.
+void sd_mutex_acquire_wait_no_vm(nrf_mutex_t* p_mutex);
+
+// Release a mutex, and raise exception on error.
+void sd_mutex_release_check(nrf_mutex_t* p_mutex);
+
+#endif // MICROPY_INCLUDED_NRF_SD_MUTEX_H
diff --git a/shared-bindings/_bleio/Characteristic.c b/shared-bindings/_bleio/Characteristic.c
index 7fcf274da0..0434368f24 100644
--- a/shared-bindings/_bleio/Characteristic.c
+++ b/shared-bindings/_bleio/Characteristic.c
@@ -128,7 +128,8 @@ STATIC mp_obj_t bleio_characteristic_add_to_service(size_t n_args, const mp_obj_
     }
     mp_get_buffer_raise(initial_value, &initial_value_bufinfo, MP_BUFFER_READ);
 
-    bleio_characteristic_obj_t *characteristic = m_new_obj(bleio_characteristic_obj_t);
+    // There may be some cleanup needed when a characteristic is gc'd, so enable finaliser.
+    bleio_characteristic_obj_t *characteristic = m_new_obj_with_finaliser(bleio_characteristic_obj_t);
     characteristic->base.type = &bleio_characteristic_type;
 
     // Range checking on max_length arg is done by the common_hal layer, because
@@ -292,8 +293,17 @@ STATIC mp_obj_t bleio_characteristic_set_cccd(mp_uint_t n_args, const mp_obj_t *
 }
 STATIC MP_DEFINE_CONST_FUN_OBJ_KW(bleio_characteristic_set_cccd_obj, 1, bleio_characteristic_set_cccd);
 
+// Cleanup on gc.
+STATIC mp_obj_t bleio_characteristic_del(mp_obj_t self_in) {
+    bleio_characteristic_obj_t *self = MP_OBJ_TO_PTR(self_in);
+    common_hal_bleio_characteristic_del(self);
+    return mp_const_none;
+}
+STATIC MP_DEFINE_CONST_FUN_OBJ_1(bleio_characteristic_del_obj, bleio_characteristic_del);
+
 
 STATIC const mp_rom_map_elem_t bleio_characteristic_locals_dict_table[] = {
+    { MP_ROM_QSTR(MP_QSTR___del__),        MP_ROM_PTR(&bleio_characteristic_del_obj) },
     { MP_ROM_QSTR(MP_QSTR_add_to_service), MP_ROM_PTR(&bleio_characteristic_add_to_service_obj) },
     { MP_ROM_QSTR(MP_QSTR_properties),     MP_ROM_PTR(&bleio_characteristic_properties_obj) },
     { MP_ROM_QSTR(MP_QSTR_uuid),           MP_ROM_PTR(&bleio_characteristic_uuid_obj) },
diff --git a/shared-bindings/_bleio/Characteristic.h b/shared-bindings/_bleio/Characteristic.h
index c4356fd4b9..60ab575724 100644
--- a/shared-bindings/_bleio/Characteristic.h
+++ b/shared-bindings/_bleio/Characteristic.h
@@ -45,5 +45,6 @@ extern bleio_descriptor_obj_t *common_hal_bleio_characteristic_get_descriptor_li
 extern bleio_service_obj_t *common_hal_bleio_characteristic_get_service(bleio_characteristic_obj_t *self);
 extern void common_hal_bleio_characteristic_add_descriptor(bleio_characteristic_obj_t *self, bleio_descriptor_obj_t *descriptor);
 extern void common_hal_bleio_characteristic_set_cccd(bleio_characteristic_obj_t *self, bool notify, bool indicate);
+extern void common_hal_bleio_characteristic_del(bleio_characteristic_obj_t *self);
 
 #endif // MICROPY_INCLUDED_SHARED_BINDINGS_BLEIO_CHARACTERISTIC_H