stmhal: L4: Add support for machine.sleep on STM32L4 MCUs.

Also raise an exception for machine.freq and machine.deepsleep on this
MCU, since they are not yet implemented.

stmhal/modmachine.c

@@ -190,6 +190,10 @@ STATIC mp_obj_t machine_freq(mp_uint_t n_args, const mp_obj_t *args) {
         // set
         mp_int_t wanted_sysclk = mp_obj_get_int(args[0]) / 1000000;
 
+        #if defined(MCU_SERIES_L4)
+        nlr_raise(mp_obj_new_exception_msg(&mp_type_NotImplementedError, "machine.freq set not supported yet"));
+        #endif
+
         // default PLL parameters that give 48MHz on PLL48CK
         uint32_t m = HSE_VALUE / 1000000, n = 336, p = 2, q = 7;
         uint32_t sysclk_source;
@@ -310,9 +314,12 @@ STATIC mp_obj_t machine_freq(mp_uint_t n_args, const mp_obj_t *args) {
 
         // set PLL as system clock source if wanted
         if (sysclk_source == RCC_SYSCLKSOURCE_PLLCLK) {
+            #if !defined(MICROPY_HW_FLASH_LATENCY)
+            #define MICROPY_HW_FLASH_LATENCY FLASH_LATENCY_5
+            #endif
             RCC_ClkInitStruct.ClockType = RCC_CLOCKTYPE_SYSCLK;
             RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
-            if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_5) != HAL_OK) {
+            if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, MICROPY_HW_FLASH_LATENCY) != HAL_OK) {
                 goto fail;
             }
         }
@@ -344,6 +351,35 @@ STATIC mp_obj_t machine_freq(mp_uint_t n_args, const mp_obj_t *args) {
 MP_DEFINE_CONST_FUN_OBJ_VAR_BETWEEN(machine_freq_obj, 0, 4, machine_freq);
 
 STATIC mp_obj_t machine_sleep(void) {
+    #if defined(MCU_SERIES_L4)
+
+    // Enter Stop 1 mode
+    __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
+
     // takes longer to wake but reduces stop current
     HAL_PWREx_EnableFlashPowerDown();
 
@@ -366,6 +402,8 @@ STATIC mp_obj_t machine_sleep(void) {
     while (__HAL_RCC_GET_SYSCLK_SOURCE() != RCC_CFGR_SWS_PLL) {
     }
 
+    #endif
+
     return mp_const_none;
 }
 MP_DEFINE_CONST_FUN_OBJ_0(machine_sleep_obj, machine_sleep);
@@ -373,7 +411,7 @@ MP_DEFINE_CONST_FUN_OBJ_0(machine_sleep_obj, machine_sleep);
 STATIC mp_obj_t machine_deepsleep(void) {
     rtc_init_finalise();
 
-#if defined(MCU_SERIES_F7)
+#if defined(MCU_SERIES_F7) || defined(MCU_SERIES_L4)
     printf("machine.deepsleep not supported yet\n");
 #else
     // We need to clear the PWR wake-up-flag before entering standby, since