diff --git a/ports/nrf/Makefile b/ports/nrf/Makefile
index ab02e12197..51179e2abb 100644
--- a/ports/nrf/Makefile
+++ b/ports/nrf/Makefile
@@ -1,19 +1,21 @@
-# Select the board to build for: if not given on the command line,
-# then default to feather52832.
-BOARD ?= feather52832
-ifeq ($(wildcard boards/$(BOARD)/.),)
-$(error Invalid BOARD specified)
+# Select the board to build for.
+ifeq ($(BOARD),)
+  $(info You must provide a BOARD parameter with 'BOARD=')
+  $(info Possible values are:)
+  $(info $(sort $(subst /.,,$(subst boards/,,$(wildcard boards/*/.)))))
+  $(error BOARD not defined)
+else
+  ifeq ($(wildcard boards/$(BOARD)/.),)
+    $(error Invalid BOARD specified)
+  endif
 endif
 
 # If SoftDevice is selected, try to use that one.
 # Default to SD132 (exact version can be set with SOFTDEV_VERSION)
-SD ?= s132
 SD_LOWER = $(shell echo $(SD) | tr '[:upper:]' '[:lower:]')
 
-# TODO: Verify that it is a valid target.
-
-# If the build directory is not given, make it reflect the board name
-BUILD ?= $(if $(SD),build-$(BOARD)-$(SD_LOWER),build-$(BOARD))
+# If the build directory with SD
+BUILD = $(if $(SD),build-$(BOARD)-$(SD_LOWER),build-$(BOARD))
 
 include ../../py/mkenv.mk
 include boards/$(BOARD)/mpconfigboard.mk
diff --git a/ports/nrf/background.c b/ports/nrf/background.c
index fc8128ca8f..094da5d9c7 100644
--- a/ports/nrf/background.c
+++ b/ports/nrf/background.c
@@ -36,19 +36,11 @@
 
 #include "tusb.h"
 
-/*------------------------------------------------------------------*/
-/* MACRO TYPEDEF CONSTANT ENUM
- *------------------------------------------------------------------*/
-
-/*------------------------------------------------------------------*/
-/* VARIABLE DECLARATION
- *------------------------------------------------------------------*/
-
-/*------------------------------------------------------------------*/
-/* FUNCTION DECLARATION
- *------------------------------------------------------------------*/
 
 void run_background_tasks(void) {
+
+#ifdef NRF52840_XXAA
     tusb_task();
     tud_cdc_flush();
+#endif
 }
diff --git a/ports/nrf/boards/feather52832/mpconfigboard.mk b/ports/nrf/boards/feather52832/mpconfigboard.mk
index dd7dd06ce8..cd991a7663 100644
--- a/ports/nrf/boards/feather52832/mpconfigboard.mk
+++ b/ports/nrf/boards/feather52832/mpconfigboard.mk
@@ -1,6 +1,7 @@
 MCU_SERIES = m4
 MCU_VARIANT = nrf52
 MCU_SUB_VARIANT = nrf52
+SD ?= s132
 SOFTDEV_VERSION ?= 2.0.1
 
 LD_FILE = boards/feather52832/custom_nrf52832_dfu_app_$(SOFTDEV_VERSION).ld
diff --git a/ports/nrf/boards/feather52840/mpconfigboard.mk b/ports/nrf/boards/feather52840/mpconfigboard.mk
index 52c0f59404..598f73631c 100644
--- a/ports/nrf/boards/feather52840/mpconfigboard.mk
+++ b/ports/nrf/boards/feather52840/mpconfigboard.mk
@@ -1,6 +1,7 @@
 MCU_SERIES = m4
 MCU_VARIANT = nrf52
 MCU_SUB_VARIANT = nrf52840
+SD ?= s140
 SOFTDEV_VERSION ?= 6.0.0
 
 BOOT_SETTING_ADDR = 0xFF000
diff --git a/ports/nrf/boards/pca10040/mpconfigboard.mk b/ports/nrf/boards/pca10040/mpconfigboard.mk
index 036969299d..79aa853494 100644
--- a/ports/nrf/boards/pca10040/mpconfigboard.mk
+++ b/ports/nrf/boards/pca10040/mpconfigboard.mk
@@ -1,6 +1,7 @@
 MCU_SERIES = m4
 MCU_VARIANT = nrf52
 MCU_SUB_VARIANT = nrf52
+SD ?= s132
 SOFTDEV_VERSION ?= 5.0.0
 
 ifeq ($(SD),)
diff --git a/ports/nrf/boards/pca10056/board.c b/ports/nrf/boards/pca10056/board.c
index 52bc5c92cc..cee269ee6f 100644
--- a/ports/nrf/boards/pca10056/board.c
+++ b/ports/nrf/boards/pca10056/board.c
@@ -36,10 +36,12 @@
 
 void board_init(void) {
 
-    // Init USB
+    // Clock
     NRF_CLOCK->LFCLKSRC = (uint32_t)((CLOCK_LFCLKSRC_SRC_Xtal << CLOCK_LFCLKSRC_SRC_Pos) & CLOCK_LFCLKSRC_SRC_Msk);
     NRF_CLOCK->TASKS_LFCLKSTART = 1UL;
 
+    // Init USB
+
 #ifdef SOFTDEVICE_PRESENT
     // TODO support Softdevice config
 #else
diff --git a/ports/nrf/boards/pca10056/mpconfigboard.h b/ports/nrf/boards/pca10056/mpconfigboard.h
index 2be1156d07..8ddff6c394 100644
--- a/ports/nrf/boards/pca10056/mpconfigboard.h
+++ b/ports/nrf/boards/pca10056/mpconfigboard.h
@@ -28,7 +28,7 @@
 
 #define MICROPY_HW_BOARD_NAME       "PCA10056"
 #define MICROPY_HW_MCU_NAME         "NRF52840"
-#define MICROPY_PY_SYS_PLATFORM     "nrf52840-PDK"
+#define MICROPY_PY_SYS_PLATFORM     "nrf52840-DK"
 
 #define MICROPY_HW_HAS_LED          (1)
 #define MICROPY_HW_HAS_SWITCH       (0)
@@ -77,3 +77,8 @@
 
 #define PORT_HEAP_SIZE                (128*1024)
 #define CIRCUITPY_AUTORELOAD_DELAY_MS 500
+
+
+// Temp (could be removed) 0: usb cdc (default), 1 : hwuart (jlink)
+#define CFG_HWUART_FOR_SERIAL        0
+
diff --git a/ports/nrf/boards/pca10056/mpconfigboard.mk b/ports/nrf/boards/pca10056/mpconfigboard.mk
index 52c0f59404..598f73631c 100644
--- a/ports/nrf/boards/pca10056/mpconfigboard.mk
+++ b/ports/nrf/boards/pca10056/mpconfigboard.mk
@@ -1,6 +1,7 @@
 MCU_SERIES = m4
 MCU_VARIANT = nrf52
 MCU_SUB_VARIANT = nrf52840
+SD ?= s140
 SOFTDEV_VERSION ?= 6.0.0
 
 BOOT_SETTING_ADDR = 0xFF000
diff --git a/ports/nrf/internal_flash.c b/ports/nrf/internal_flash.c
index 56377c9734..35e0ae8b75 100644
--- a/ports/nrf/internal_flash.c
+++ b/ports/nrf/internal_flash.c
@@ -74,7 +74,6 @@ void internal_flash_init(void) {
         port_pin_set_config(MICROPY_HW_LED_MSC, &pin_conf);
         port_pin_set_output_level(MICROPY_HW_LED_MSC, false);
     #endif
-//    flash_init(&internal_flash_desc, NVMCTRL);
 }
 
 uint32_t internal_flash_get_block_size(void) {
diff --git a/ports/nrf/internal_flash.h b/ports/nrf/internal_flash.h
index e83b39d573..3811815e29 100644
--- a/ports/nrf/internal_flash.h
+++ b/ports/nrf/internal_flash.h
@@ -33,17 +33,17 @@
 
 #define FLASH_ROOT_POINTERS
 
-#define FLASH_PAGE_SIZE             0x1000
-#define CIRCUITPY_INTERNAL_NVM_SIZE 0
+#define FLASH_PAGE_SIZE                 0x1000
+#define CIRCUITPY_INTERNAL_NVM_SIZE     0
 
-#define INTERNAL_FLASH_SYSTICK_MASK    (0x1ff) // 512ms
-#define INTERNAL_FLASH_IDLE_TICK(tick) (((tick) & INTERNAL_FLASH_SYSTICK_MASK) == 2)
+#define INTERNAL_FLASH_SYSTICK_MASK     (0x1ff) // 512ms
+#define INTERNAL_FLASH_IDLE_TICK(tick)  (((tick) & INTERNAL_FLASH_SYSTICK_MASK) == 2)
 
-void internal_flash_init(void);
-uint32_t internal_flash_get_block_size(void);
-uint32_t internal_flash_get_block_count(void);
-void internal_flash_irq_handler(void);
-void internal_flash_flush(void);
+void      internal_flash_init(void);
+uint32_t  internal_flash_get_block_size(void);
+uint32_t  internal_flash_get_block_count(void);
+void      internal_flash_irq_handler(void);
+void      internal_flash_flush(void);
 
 // these return 0 on success, non-zero on error
 mp_uint_t internal_flash_read_blocks(uint8_t *dest, uint32_t block_num, uint32_t num_blocks);
diff --git a/ports/nrf/mphalport.c b/ports/nrf/mphalport.c
index e13554d7b5..85e2867553 100644
--- a/ports/nrf/mphalport.c
+++ b/ports/nrf/mphalport.c
@@ -32,13 +32,20 @@
 #include "py/mperrno.h"
 #include "hal_uart.h"
 
-#ifndef NRF52840_XXAA
+#if !defined( NRF52840_XXAA) || ( defined(CFG_HWUART_FOR_SERIAL) && CFG_HWUART_FOR_SERIAL == 1 )
 
 #define UART_INSTANCE   UART_BASE(0)
 
 #if (MICROPY_PY_BLE_NUS == 0)
 int mp_hal_stdin_rx_chr(void) {
     for (;;) {
+        #ifdef MICROPY_VM_HOOK_LOOP
+            MICROPY_VM_HOOK_LOOP
+        #endif
+        // if (reload_requested) {
+        //     return CHAR_CTRL_D;
+        // }
+
         if ( hal_uart_available(UART_INSTANCE) ) {
           uint8_t ch;
           hal_uart_char_read(UART_INSTANCE, &ch);
@@ -99,6 +106,7 @@ int mp_hal_stdin_rx_chr(void) {
         // if (reload_requested) {
         //     return CHAR_CTRL_D;
         // }
+
         if (tud_cdc_available()) {
             #ifdef MICROPY_HW_LED_RX
             gpio_toggle_pin_level(MICROPY_HW_LED_RX);
@@ -106,6 +114,8 @@ int mp_hal_stdin_rx_chr(void) {
             return tud_cdc_read_char();
         }
     }
+
+    return 0;
 }
 
 bool mp_hal_stdin_any(void) {
@@ -114,20 +124,21 @@ bool mp_hal_stdin_any(void) {
 
 void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
 
-//    #ifdef MICROPY_HW_LED_TX
-//    gpio_toggle_pin_level(MICROPY_HW_LED_TX);
-//    #endif
-//
-//    #ifdef CIRCUITPY_BOOT_OUTPUT_FILE
-//    if (boot_output_file != NULL) {
-//        UINT bytes_written = 0;
-//        f_write(boot_output_file, str, len, &bytes_written);
-//    }
-//    #endif
+    #ifdef MICROPY_HW_LED_TX
+    gpio_toggle_pin_level(MICROPY_HW_LED_TX);
+    #endif
+
+    #ifdef CIRCUITPY_BOOT_OUTPUT_FILE
+    if (boot_output_file != NULL) {
+        UINT bytes_written = 0;
+        f_write(boot_output_file, str, len, &bytes_written);
+    }
+    #endif
 
     tud_cdc_write(str, len);
 }
 
+// TODO use stdout_helper.c
 void mp_hal_stdout_tx_strn_cooked(const char *str, size_t len) {
     while (len--) {
         if (*str == '\n') {
@@ -137,9 +148,11 @@ void mp_hal_stdout_tx_strn_cooked(const char *str, size_t len) {
     }
 }
 
-#endif
-
 void mp_hal_stdout_tx_str(const char *str) {
     mp_hal_stdout_tx_strn(str, strlen(str));
 }
 
+#endif
+
+
+
diff --git a/ports/nrf/supervisor/serial.c b/ports/nrf/supervisor/serial.c
index 080f77644a..e6c43b58aa 100644
--- a/ports/nrf/supervisor/serial.c
+++ b/ports/nrf/supervisor/serial.c
@@ -36,7 +36,7 @@
 #include "ble_uart.h"
 #endif
 
-#ifndef NRF52840_XXAA
+#if !defined( NRF52840_XXAA) || ( defined(CFG_HWUART_FOR_SERIAL) && CFG_HWUART_FOR_SERIAL == 1 )
 
 void serial_init(void) {
 
@@ -91,7 +91,7 @@ void serial_write(const char* text) {
 #include "tusb.h"
 
 void serial_init(void) {
-    // usb should be initialized in board_init()
+    // usb is already initialized in board_init()
 }