stm32/modmachine: Get machine.sleep working on L4 MCUs.

When waking from stop mode most of the system is still in the same state as
before entering stop, so only minimal configuration is needed to bring the
system clock back online.

ports/stm32/modmachine.c

@@ -483,35 +483,11 @@ MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(machine_freq_obj, 0, 4, machine_freq);
 
 STATIC mp_obj_t machine_sleep(void) {
     #if defined(STM32L4)
-
-    // Enter Stop 1 mode
+    // Configure the MSI as the clock source after waking up
     __HAL_RCC_WAKEUPSTOP_CLK_CONFIG(RCC_STOP_WAKEUPCLOCK_MSI);
-    HAL_PWR_EnterSTOPMode(PWR_LOWPOWERREGULATOR_ON, PWR_STOPENTRY_WFI);
-
-    // reconfigure system clock after wakeup
-    // Enable Power Control clock
-    __HAL_RCC_PWR_CLK_ENABLE();
-
-    // Get the Oscillators configuration according to the internal RCC registers
-    RCC_OscInitTypeDef RCC_OscInitStruct = {0};
-    HAL_RCC_GetOscConfig(&RCC_OscInitStruct);
-    RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_MSI;
-    RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
-    HAL_RCC_OscConfig(&RCC_OscInitStruct);
-
-    // Get the Clocks configuration according to the internal RCC registers
-    RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};
-    uint32_t pFLatency = 0;
-    HAL_RCC_GetClockConfig(&RCC_ClkInitStruct, &pFLatency);
-
-    // Select PLL as system clock source and configure the HCLK, PCLK1 and PCLK2 clock dividers
-    RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_SYSCLK;
-    RCC_ClkInitStruct.SYSCLKSource  = RCC_SYSCLKSOURCE_PLLCLK;
-    HAL_RCC_ClockConfig(&RCC_ClkInitStruct, pFLatency);
-
-    #else
+    #endif
 
-    #if !defined(STM32F0)
+    #if !defined(STM32F0) && !defined(STM32L4)
     // takes longer to wake but reduces stop current
     HAL_PWREx_EnableFlashPowerDown();
     #endif
@@ -538,10 +514,12 @@ STATIC mp_obj_t machine_sleep(void) {
 
     #else
 
+    #if !defined(STM32L4)
     // enable HSE
     __HAL_RCC_HSE_CONFIG(MICROPY_HW_CLK_HSE_STATE);
     while (!__HAL_RCC_GET_FLAG(RCC_FLAG_HSERDY)) {
     }
+    #endif
 
     // enable PLL
     __HAL_RCC_PLL_ENABLE();
@@ -559,8 +537,6 @@ STATIC mp_obj_t machine_sleep(void) {
 
     #endif
 
-    #endif
-
     return mp_const_none;
 }
 MP_DEFINE_CONST_FUN_OBJ_0(machine_sleep_obj, machine_sleep);