stm32/powerctrlboot: Support STM32WL system clock from HSE+PLL.

Switches default on the NUCLEO_WL55 board to use the HSE oscillator powered
from PB0_VDDTCXO pin.

Build-time configuration can select from MSI internal oscillator (previous
default), HSE via crystal, or HSE bypass with TCXO powered from PB0_VDDTCXO
pin (new default)
Signed-off-by: Angus Gratton <angus@redyak.com.au>

ports/stm32/boards/NUCLEO_WL55/mpconfigboard.h

@@ -28,6 +28,13 @@
 #define MICROPY_HW_RTC_USE_LSE                  (1)
 #define MICROPY_HW_RTC_USE_US                   (1)
 
+// Use external 32MHz TCXO + PLL as system clock source
+// (If unset, board will use the internal MSI oscillator instead.)
+#define MICROPY_HW_CLK_USE_HSE                  (1)
+
+// HSE bypass for STM32WL5x means TCXO is powered from PB0_VDDTCXO pin
+#define MICROPY_HW_CLK_USE_BYPASS               (1)
+
 // UART buses
 #define MICROPY_HW_UART1_TX                     (pin_B6)    // Arduino D1, pin 7 on CN9
 #define MICROPY_HW_UART1_RX                     (pin_B7)    // Arduino D0, pin 8 on CN9

ports/stm32/boards/NUCLEO_WL55/pins.csv

@@ -14,7 +14,8 @@
 ,PA13
 ,PA14
 ,PA15
-,PB0
+# in the default board configuration, PB0 must stay muxed to analog for HSE VDDTCXO function
+,-PB0
 ,PB1
 ,PB2
 ,PB3

ports/stm32/mpconfigboard_common.h

@@ -471,8 +471,12 @@
 #define MICROPY_HW_RCC_HSI_STATE (RCC_HSI_OFF)
 #define MICROPY_HW_RCC_FLAG_HSxRDY (RCC_FLAG_HSERDY)
 #if MICROPY_HW_CLK_USE_BYPASS
+#if !defined(STM32WL)
 #define MICROPY_HW_RCC_HSE_STATE (RCC_HSE_BYPASS)
 #else
+#define MICROPY_HW_RCC_HSE_STATE (RCC_HSE_BYPASS_PWR)
+#endif
+#else
 #define MICROPY_HW_RCC_HSE_STATE (RCC_HSE_ON)
 #endif
 #endif

ports/stm32/powerctrlboot.c

@@ -460,13 +460,71 @@ void SystemClock_Config(void) {
 #include "stm32wlxx_ll_utils.h"
 
 void SystemClock_Config(void) {
-    // Set flash latency
+    // Set flash latency (2 wait states, sysclk > 36MHz)
     LL_FLASH_SetLatency(LL_FLASH_LATENCY_2);
     while (LL_FLASH_GetLatency() != LL_FLASH_LATENCY_2) {
     }
 
     LL_PWR_SetRegulVoltageScaling(LL_PWR_REGU_VOLTAGE_SCALE1);
 
+    #if MICROPY_HW_CLK_USE_HSE
+    // Enable the 32MHz external oscillator and 48MHZ SYSCLK via PLL
+
+    #if MICROPY_HW_CLK_USE_BYPASS
+    // Use "bypass power" option, port PB0_VDDTCXO supplies TCXO
+    // (STM32WL5x has no other HSE bypass mode.)
+
+    // "PB0 must be configured in analog mode prior enabling the HSE"
+    //
+    // Note: PB0 analog mode muxes PB0_VDDTCXO pin to the VDDTCXO regulator, set
+    // to default voltage of 1.7V.  Changing this voltage requires initializing
+    // the SUBGHZ radio and sending a Set_Tcxo command to it.
+    //
+    // For the Nucelo-WL55 board, ST uses the NDK "NT2016SF-32M-END5875A" TCXO
+    // which has no publicly available datasheet. However, the ST code for this
+    // board always keeps the pin at the default 1.7V voltage level so changing
+    // the level would only be needed if a different TCXO is used.
+    //
+    // (Note also that setting pin PB0 as a push-pull GPIO output is technically
+    // possible too, but 3.3V will be too high for many TCXOs.)
+    mp_hal_pin_config(pin_B0, MP_HAL_PIN_MODE_ANALOG, MP_HAL_PIN_PULL_NONE, 0);
+
+    LL_RCC_HSE_EnableTcxo();
+
+    #endif // MICROPY_HW_CLK_USE_BYPASS
+
+    LL_RCC_HSE_Enable();
+    while (!LL_RCC_HSE_IsReady()) {
+        // Wait for HSE Ready signal
+    }
+
+    // Configure PLL for a 48MHz SYSCLK
+    #define PLLM (HSE_VALUE / 16000000) // VCO input 16MHz (recommended in ST docs)
+    #define PLLN (6) // 7*8MHz = 96MHz
+    #define PLLP (2) // f_P = 48MHz
+    #define PLLQ (2) // f_Q = 48MHz
+    #define PLLR (2) // f_R = 48MHz
+    RCC->PLLCFGR =
+        (PLLR - 1) << RCC_PLLCFGR_PLLR_Pos | RCC_PLLCFGR_PLLREN
+            | (PLLQ - 1) << RCC_PLLCFGR_PLLQ_Pos | RCC_PLLCFGR_PLLQEN
+            | (PLLP - 1) << RCC_PLLCFGR_PLLP_Pos | RCC_PLLCFGR_PLLPEN
+            | PLLN << RCC_PLLCFGR_PLLN_Pos
+            | (PLLM - 1) << RCC_PLLCFGR_PLLM_Pos
+            | LL_RCC_PLLSOURCE_HSE;
+
+    LL_RCC_PLL_Enable();
+    LL_RCC_PLL_EnableDomain_SYS();
+    while (!LL_RCC_PLL_IsReady()) {
+        // Wait for PLL to lock
+    }
+
+    LL_RCC_SetSysClkSource(LL_RCC_SYS_CLKSOURCE_PLL);
+    while (LL_RCC_GetSysClkSource() != LL_RCC_SYS_CLKSOURCE_STATUS_PLL) {
+        // Wait for system clock source to switch
+    }
+
+    #else // Use MSI as 48MHz source for SYSCLK
+
     // Enable MSI
     LL_RCC_MSI_Enable();
     while (!LL_RCC_MSI_IsReady()) {
@@ -482,6 +540,8 @@ void SystemClock_Config(void) {
     while (LL_RCC_GetSysClkSource() != LL_RCC_SYS_CLKSOURCE_STATUS_MSI) {
     }
 
+    #endif // MICROPY_HW_CLK_USE_HSE
+
     // Set bus dividers
     LL_RCC_SetAHBPrescaler(LL_RCC_SYSCLK_DIV_1);
     LL_RCC_SetAHB3Prescaler(LL_RCC_SYSCLK_DIV_1);