stm32: Allow a board to configure the HSE in bypass mode.

To use HSE bypass mode the board should define:

    #define MICROPY_HW_CLK_USE_BYPASS (1)

If this is not defined, or is defined to 0, then HSE oscillator mode is
used.

ports/stm32/modmachine.c

@@ -377,7 +377,7 @@ STATIC mp_obj_t machine_freq(size_t n_args, const mp_obj_t *args) {
         // even if we don't use the PLL for the system clock, we still need it for USB, RNG and SDIO
         RCC_OscInitTypeDef RCC_OscInitStruct;
         RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
-        RCC_OscInitStruct.HSEState = RCC_HSE_ON;
+        RCC_OscInitStruct.HSEState = MICROPY_HW_CLK_HSE_STATE;
         RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
         RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
         RCC_OscInitStruct.PLL.PLLM = m;
@@ -500,7 +500,7 @@ STATIC mp_obj_t machine_sleep(void) {
     // reconfigure the system clock after waking up
 
     // enable HSE
-    __HAL_RCC_HSE_CONFIG(RCC_HSE_ON);
+    __HAL_RCC_HSE_CONFIG(MICROPY_HW_CLK_HSE_STATE);
     while (!__HAL_RCC_GET_FLAG(RCC_FLAG_HSERDY)) {
     }
 

ports/stm32/mpconfigboard_common.h

@@ -136,6 +136,13 @@
 #error Unsupported MCU series
 #endif
 
+// Configure HSE for bypass or oscillator
+#if MICROPY_HW_CLK_USE_BYPASS
+#define MICROPY_HW_CLK_HSE_STATE (RCC_HSE_BYPASS)
+#else
+#define MICROPY_HW_CLK_HSE_STATE (RCC_HSE_ON)
+#endif
+
 #if MICROPY_HW_ENABLE_INTERNAL_FLASH_STORAGE
 // Provide block device macros if internal flash storage is enabled
 #define MICROPY_HW_BDEV_IOCTL flash_bdev_ioctl

ports/stm32/stm32_it.c

@@ -369,7 +369,7 @@ STATIC void OTG_CMD_WKUP_Handler(PCD_HandleTypeDef *pcd_handle) {
     /* Configures system clock after wake-up from STOP: enable HSE, PLL and select
     PLL as system clock source (HSE and PLL are disabled in STOP mode) */
 
-    __HAL_RCC_HSE_CONFIG(RCC_HSE_ON);
+    __HAL_RCC_HSE_CONFIG(MICROPY_HW_CLK_HSE_STATE);
 
     /* Wait till HSE is ready */
     while(__HAL_RCC_GET_FLAG(RCC_FLAG_HSERDY) == RESET)

ports/stm32/system_stm32.c

@@ -404,7 +404,7 @@ void SystemClock_Config(void)
     /* Enable HSE Oscillator and activate PLL with HSE as source */
     #if defined(STM32F4) || defined(STM32F7) || defined(STM32H7)
     RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
-    RCC_OscInitStruct.HSEState = RCC_HSE_ON;
+    RCC_OscInitStruct.HSEState = MICROPY_HW_CLK_HSE_STATE;
     RCC_OscInitStruct.HSIState = RCC_HSI_OFF;
     #if defined(STM32H7)
     RCC_OscInitStruct.CSIState = RCC_CSI_OFF;