From 4d1161b689753c76e1c661fc2c4d52b349d0e556 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Bora=20=C3=96zgen?= <oezgen@nantis.de>
Date: Tue, 9 Feb 2021 14:04:48 +0100
Subject: [PATCH] Add HSE support to STM32 RTC

---
 targets/TARGET_STM/rtc_api.c     | 13 ++++++++++++-
 targets/TARGET_STM/rtc_api_hal.h |  8 +++++++-
 2 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/targets/TARGET_STM/rtc_api.c b/targets/TARGET_STM/rtc_api.c
index a3309c261d..698088b557 100644
--- a/targets/TARGET_STM/rtc_api.c
+++ b/targets/TARGET_STM/rtc_api.c
@@ -62,7 +62,18 @@ void rtc_init(void)
     while (LL_HSEM_1StepLock(HSEM, CFG_HW_RCC_SEMID)) {
     }
 #endif /* DUAL_CORE */
-#if MBED_CONF_TARGET_LSE_AVAILABLE
+#if RTC_FROM_HSE
+#define RTC_HSE_DIV (HSE_VALUE / RTC_CLOCK)
+#if RTC_HSE_DIV > 31
+#error "HSE value too high for RTC"
+#endif
+    (void)RCC_OscInitStruct;
+    PeriphClkInitStruct.PeriphClockSelection = RCC_PERIPHCLK_RTC;
+    PeriphClkInitStruct.RTCClockSelection = (RCC_RTCCLKSOURCE_HSE_DIVX | RTC_HSE_DIV << 16);
+    if (HAL_RCCEx_PeriphCLKConfig(&PeriphClkInitStruct) != HAL_OK) {
+        error("PeriphClkInitStruct RTC failed with HSE\n");
+    }
+#elif MBED_CONF_TARGET_LSE_AVAILABLE
     RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_LSE;
     RCC_OscInitStruct.PLL.PLLState   = RCC_PLL_NONE;
 #if MBED_CONF_TARGET_LSE_BYPASS
diff --git a/targets/TARGET_STM/rtc_api_hal.h b/targets/TARGET_STM/rtc_api_hal.h
index 086e64dc98..eaf57fccd9 100644
--- a/targets/TARGET_STM/rtc_api_hal.h
+++ b/targets/TARGET_STM/rtc_api_hal.h
@@ -38,7 +38,9 @@
 extern "C" {
 #endif
 
-#if MBED_CONF_TARGET_LSE_AVAILABLE
+#if RTC_FROM_HSE
+#define RTC_CLOCK 1000000U
+#elif MBED_CONF_TARGET_LSE_AVAILABLE
 #define RTC_CLOCK LSE_VALUE
 #else
 #define RTC_CLOCK LSI_VALUE
@@ -47,7 +49,11 @@ extern "C" {
 #if DEVICE_LPTICKER && !MBED_CONF_TARGET_LPTICKER_LPTIM
 /* PREDIV_A : 7-bit asynchronous prescaler */
 /* PREDIV_A is set to set LPTICKER frequency to RTC_CLOCK/4 */
+#if RTC_FROM_HSE
+#define PREDIV_A_VALUE 124
+#else
 #define PREDIV_A_VALUE 3
+#endif
 
 /** Read RTC counter with sub second precision
  *