HAL Timebase, Power, Clock: semaphore guarded access to clock and power modes, better sleep mode. (#307)

firmware/targets/f4/api-hal/api-hal-clock.c

@@ -0,0 +1,27 @@
+#include <api-hal-clock.h>
+
+#include <stm32wbxx_ll_rcc.h>
+
+void api_hal_clock_switch_to_hsi() {
+    LL_RCC_HSI_Enable( );
+
+    while(!LL_RCC_HSI_IsReady());
+
+    LL_RCC_SetSysClkSource(LL_RCC_SYS_CLKSOURCE_HSI);
+    LL_RCC_SetSMPSClockSource(LL_RCC_SMPS_CLKSOURCE_HSI);
+
+    while (LL_RCC_GetSysClkSource() != LL_RCC_SYS_CLKSOURCE_STATUS_HSI);
+}
+
+void api_hal_clock_switch_to_pll() {
+    LL_RCC_HSE_Enable();
+    LL_RCC_PLL_Enable();
+
+    while(!LL_RCC_HSE_IsReady());
+    while(!LL_RCC_PLL_IsReady());
+
+    LL_RCC_SetSysClkSource(LL_RCC_SYS_CLKSOURCE_PLL);
+    LL_RCC_SetSMPSClockSource(LL_RCC_SMPS_CLKSOURCE_HSE);
+
+    while (LL_RCC_GetSysClkSource() != LL_RCC_SYS_CLKSOURCE_STATUS_PLL);
+}