diff --git a/lib/nrfutil b/lib/nrfutil
index d48561b073..9e7dfb28a5 160000
--- a/lib/nrfutil
+++ b/lib/nrfutil
@@ -1 +1 @@
-Subproject commit d48561b07386132b849d0125b0ff6a532d833d8b
+Subproject commit 9e7dfb28a5c6f3d7a19340971b32e0c2b4128ecf
diff --git a/ports/nrf/boards/feather52/mpconfigboard.mk b/ports/nrf/boards/feather52/mpconfigboard.mk
index 1e3aa5a249..7ff8684d22 100644
--- a/ports/nrf/boards/feather52/mpconfigboard.mk
+++ b/ports/nrf/boards/feather52/mpconfigboard.mk
@@ -31,11 +31,11 @@ __check_defined = \
 .PHONY: dfu-gen dfu-flash boot-flash
 
 dfu-gen:
-	$(NRFUTIL) dfu genpkg --dev-type 0x0052 --application $(BUILD)/$(OUTPUT_FILENAME).hex $(BUILD)/dfu-package.zip
+	$(NRFUTIL) dfu genpkg --sd-req 0xFFFE --dev-type 0x0052 --application $(BUILD)/$(OUTPUT_FILENAME).hex $(BUILD)/dfu-package.zip
 
 dfu-flash:
 	@:$(call check_defined, SERIAL, example: SERIAL=/dev/ttyUSB0)
-	$(NRFUTIL) dfu serial --package $(BUILD)/dfu-package.zip -p $(SERIAL) -b 115200
+	$(NRFUTIL) dfu serial --package $(BUILD)/dfu-package.zip -p $(SERIAL) -b 115200 --singlebank
 
 boot-flash:
 	@:$(call check_defined, SERIAL, example: SERIAL=/dev/ttyUSB0)
diff --git a/ports/nrf/boards/feather52840/mpconfigboard_s140.mk b/ports/nrf/boards/feather52840/mpconfigboard_s140.mk
index 2a3c98e7dc..c49e3222eb 100644
--- a/ports/nrf/boards/feather52840/mpconfigboard_s140.mk
+++ b/ports/nrf/boards/feather52840/mpconfigboard_s140.mk
@@ -36,7 +36,7 @@ dfu-gen:
 
 dfu-flash:
 	@:$(call check_defined, SERIAL, example: SERIAL=/dev/ttyUSB0)
-	$(NRFUTIL) --verbose dfu serial --package $(BUILD)/dfu-package.zip -p $(SERIAL) -b 115200
+	$(NRFUTIL) --verbose dfu serial --package $(BUILD)/dfu-package.zip -p $(SERIAL) -b 115200 --singlebank
 
 boot-flash:
 	nrfjprog --program $(BOOT_UART_FILE).hex -f nrf52 --chiperase --reset
diff --git a/ports/nrf/hal/hal_uart.c b/ports/nrf/hal/hal_uart.c
index e8d4230816..b0a57a2a6e 100644
--- a/ports/nrf/hal/hal_uart.c
+++ b/ports/nrf/hal/hal_uart.c
@@ -156,6 +156,10 @@ void hal_uart_init(NRF_UART_Type * p_instance, hal_uart_init_t const * p_uart_in
     NVIC_EnableIRQ(p_uart_init->irq_num);
 }
 
+bool hal_uart_inited(NRF_UART_Type * p_instance)
+{
+    return !(p_instance->PSELTXD & (1 << 31)) && !(p_instance->PSELRXD & (1 << 31));
+}
 
 void UARTE0_UART0_IRQHandler(void)
 {
diff --git a/ports/nrf/hal/hal_uart.h b/ports/nrf/hal/hal_uart.h
index 76c09b335f..47f10cce1b 100644
--- a/ports/nrf/hal/hal_uart.h
+++ b/ports/nrf/hal/hal_uart.h
@@ -117,6 +117,7 @@ typedef struct
 typedef void (*uart_complete_cb)(void);
 
 void hal_uart_init(NRF_UART_Type * p_instance, hal_uart_init_t const * p_uart_init);
+bool hal_uart_inited(NRF_UART_Type * p_instance);
 
 hal_uart_error_t hal_uart_char_write(NRF_UART_Type * p_instance, uint8_t ch);
 
diff --git a/ports/nrf/mpconfigport.h b/ports/nrf/mpconfigport.h
index a463108b87..ac5741f771 100644
--- a/ports/nrf/mpconfigport.h
+++ b/ports/nrf/mpconfigport.h
@@ -330,6 +330,6 @@ extern const struct _mp_obj_module_t ble_module;
 #include <alloca.h>
 
 #define MICROPY_PIN_DEFS_PORT_H "pin_defs_nrf5.h"
-//#define CIRCUITPY_BOOT_OUTPUT_FILE "/boot_out.txt"
+#define CIRCUITPY_BOOT_OUTPUT_FILE "/boot_out.txt"
 
 #endif
diff --git a/ports/nrf/mphalport.c b/ports/nrf/mphalport.c
index 957d3535d2..824ce859ae 100644
--- a/ports/nrf/mphalport.c
+++ b/ports/nrf/mphalport.c
@@ -65,9 +65,23 @@ bool mp_hal_stdin_any(void) {
 }
 
 void mp_hal_stdout_tx_strn(const char *str, mp_uint_t len) {
-  while(len--) {
-    hal_uart_char_write(UART_INSTANCE, *str++);
-  }
+
+//    #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
+
+    if ( hal_uart_inited(UART_INSTANCE) ) {
+        while(len--) {
+            hal_uart_char_write(UART_INSTANCE, *str++);
+        }
+    }
 }
 
 void mp_hal_stdout_tx_strn_cooked(const char *str, mp_uint_t len) {