diff --git a/stmhal/boards/LIMIFROG/board_init.c b/stmhal/boards/LIMIFROG/board_init.c
new file mode 100644
index 0000000000000000000000000000000000000000..72f920842467a181924478722222edc29d8aea36
--- /dev/null
+++ b/stmhal/boards/LIMIFROG/board_init.c
@@ -0,0 +1,154 @@
+// The code is this file allows the user to enter DFU mode when the board
+// starts up, by connecting POS10 on the external connector to GND.
+// The code itself is taken from the LimiFrog software repository found at
+// https://github.com/LimiFrog/LimiFrog-SW, and the original license header
+// is copied below.
+
+#include STM32_HAL_H
+
+static void LBF_DFU_If_Needed(void);
+
+void LIMIFROG_board_early_init(void) {
+ LBF_DFU_If_Needed();
+}
+
+/*******************************************************************************
+ * LBF_DFU_If_Needed.c
+ *
+ * (c)2015 LimiFrog / CYMEYA
+ * This program is licensed under the terms of the MIT License.
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND.
+ * Please refer to the License File LICENSE.txt located at the root of this
+ * project for full licensing conditions,
+ * or visit https://opensource.org/licenses/MIT.
+ ******************************************************************************/
+
+#define __LIMIFROG_02
+
+/* ==== BTLE (excl UART) ======================================== */
+// PC9 = BT_RST (active high)
+
+#define BT_RST_PIN GPIO_PIN_9
+#define BT_RST_PORT GPIOC
+
+// Position 10
+#ifdef __LIMIFROG_01
+ #define CONN_POS10_PIN GPIO_PIN_9
+ #define CONN_POS10_PORT GPIOB
+#else
+ #define CONN_POS10_PIN GPIO_PIN_8
+ #define CONN_POS10_PORT GPIOB
+#endif
+
+static inline void GPIO_HIGH(GPIO_TypeDef* GPIOx, uint16_t GPIO_Pin)
+{
+ GPIOx->BSRR = (uint32_t)GPIO_Pin;
+}
+
+static inline int IS_GPIO_RESET(GPIO_TypeDef* GPIOx, uint16_t GPIO_Pin)
+{
+ GPIO_PinState bitstatus;
+ if((GPIOx->IDR & GPIO_Pin) != (uint32_t)GPIO_PIN_RESET)
+ {
+ bitstatus = GPIO_PIN_SET;
+ }
+ else
+ {
+ bitstatus = GPIO_PIN_RESET;
+ }
+ return (bitstatus==GPIO_PIN_RESET);
+}
+
+/**************************************************************
+ RATIONALE FOR THIS FUNCTION :
+
+ - The STM32 embeds in ROM a bootloader that allows to
+ obtain code and boot from a number of different interfaces,
+ including USB in a mode called "DFU" (Device Frimware Update)
+ [see AN3606 from ST for full details]
+ This bootloader code is executed instead of the regular
+ application code when pin BOOT0 is pulled-up (which on
+ LimiFrog0.2 is achieved by pressing the general-purpose
+ pushbutton switch on the side.
+ - The bootloader monitors a number of IOs of the STM32 to decide
+ from which interface it should boot.
+ - Problem in LimiFrog (up to versions 0.2a at least): upon
+ power-up the BLE modules generates some activity on UART3,
+ which is part of the pins monitored by the STM32.
+ This misleads the bootloader in trying to boot from UART3
+ and, as a result, not continuing with booting from USB.
+
+ - This code implements an alternative solution to launch the
+ bootloader while making sure UART3 remains stable.
+ - The idea it to start application code with a check, prior to any
+ other applicative code, of whether USB bootload is required (as
+ flagged by a GPIO pulled low at reset, in the same way as BOOT0).
+ The hadware reset pin of BLE is asserted (so that now it won't
+ generate any acitivity on UART3), and if USB bootload is required :
+ bootload ROM is remapped at address 0x0, stack pointer is
+ updated and the code is branched to the start of the bootloader.
+ - This code is run prior to any applicative configuration of clocks,
+ IRQs etc. -- the STM32 is therefore still running from MSI
+
+ THIS FUNCTION MAY BE SUPPRESSED IF YOU NEVER NEED TO BOOT DFU MODE
+
+ ********************************************************************/
+
+static void LBF_DFU_If_Needed(void)
+{
+
+
+ GPIO_InitTypeDef GPIO_InitStruct;
+
+
+ // Initialize and assert pin BTLE_RST
+ // (hw reset to BLE module, so it won't drive UART3)
+
+ __GPIOC_CLK_ENABLE();
+ GPIO_InitStruct.Mode = GPIO_MODE_OUTPUT_PP;
+ GPIO_InitStruct.Pull = GPIO_NOPULL;
+ GPIO_InitStruct.Speed = GPIO_SPEED_LOW;
+ GPIO_InitStruct.Pin = BT_RST_PIN;
+ HAL_GPIO_Init(BT_RST_PORT, &GPIO_InitStruct);
+
+ GPIO_HIGH(BT_RST_PORT, BT_RST_PIN); // assert BTLE reset
+
+
+ /* -- Bootloader will be called if position 10 on the extension port
+ is actively pulled low -- */
+ // Note - this is an arbitrary choice, code could be modified to
+ // monitor another GPIO of the STM32 and/or decide that active level
+ // is high rather than low
+
+
+ // Initialize Extension Port Position 10 = PB8 (bears I2C1_SCL)
+ // Use weak pull-up to detect if pin is externally pulled low
+
+ __GPIOB_CLK_ENABLE();
+ GPIO_InitStruct.Mode = GPIO_MODE_INPUT;
+ GPIO_InitStruct.Pull = GPIO_PULLUP;
+ GPIO_InitStruct.Pin = CONN_POS10_PIN;
+ HAL_GPIO_Init(CONN_POS10_PORT, &GPIO_InitStruct);
+
+ // If selection pin pulled low...
+ if ( IS_GPIO_RESET(CONN_POS10_PORT, CONN_POS10_PIN ))
+
+ {
+ // Remap bootloader ROM (ie System Flash) to address 0x0
+ SYSCFG->MEMRMP = 0x00000001;
+
+ // Init stack pointer with value residing at ROM base
+ asm (
+ "LDR R0, =0x00000000\n\t" // load ROM base address"
+ "LDR SP,[R0, #0]\n\t" // assign main stack pointer"
+ );
+
+ // Jump to address pointed by 0x00000004 -- */
+
+ asm (
+ "LDR R0,[R0, #4]\n\t" // load bootloader address
+ "BX R0\n\t"
+ );
+
+ }
+}
diff --git a/stmhal/boards/LIMIFROG/mpconfigboard.h b/stmhal/boards/LIMIFROG/mpconfigboard.h
index 8456e0351392f82b8bec3ef25a31e74ff3e7addb..782c9c90f872079cfe56f58417a6ffef068a7192 100644
--- a/stmhal/boards/LIMIFROG/mpconfigboard.h
+++ b/stmhal/boards/LIMIFROG/mpconfigboard.h
@@ -16,6 +16,9 @@
#define MICROPY_HW_ENABLE_DAC (0)
#define MICROPY_HW_ENABLE_CAN (0)
+#define MICROPY_BOARD_EARLY_INIT LIMIFROG_board_early_init
+void LIMIFROG_board_early_init(void);
+
// MSI is used and is 4MHz
#define MICROPY_HW_CLK_PLLM (1)
#define MICROPY_HW_CLK_PLLN (40)