From 08efc1f0e50c4b82d4ccc117a87bc594fd540e1f Mon Sep 17 00:00:00 2001
From: Ethan Zonca <ez@ethanzonca.com>
Date: Mon, 9 May 2016 20:52:08 -0400
Subject: [PATCH] Add clock trimming for internal HSI48; move internal/external
 osc selection to makefile

---
 Makefile   |  5 +++++
 Src/main.c | 38 +++++++++++++++++++++++++++++++++-----
 2 files changed, 38 insertions(+), 5 deletions(-)

diff --git a/Makefile b/Makefile
index 3e766b0..e05d07e 100644
--- a/Makefile
+++ b/Makefile
@@ -34,6 +34,11 @@ USB_INCLUDES += -IMiddlewares/ST/STM32_USB_Device_Library/Class/CDC/Inc
 
 # USER_CFLAGS: user C flags (enable warnings, enable debug info)
 USER_CFLAGS = -Wall -g -ffunction-sections -fdata-sections -Os
+
+ifeq ($(INTERNAL_OSCILLATOR), 1)
+    USER_CFLAGS += -DINTERNAL_OSCILLATOR
+endif
+
 # USER_LDFLAGS:  user LD flags
 USER_LDFLAGS = -fno-exceptions -ffunction-sections -fdata-sections -Wl,--gc-sections
 
diff --git a/Src/main.c b/Src/main.c
index c4d1534..aeaa676 100644
--- a/Src/main.c
+++ b/Src/main.c
@@ -42,8 +42,6 @@
 #include "slcan.h"
 #include "led.h"
 
-//#define INTERNAL_OSCILLATOR
-#define EXTERNAL_OSCILLATOR
 
 /* USER CODE END Includes */
 
@@ -155,7 +153,7 @@ void SystemClock_Config(void)
     PeriphClkInit.UsbClockSelection = RCC_USBCLKSOURCE_HSI48;
 
 
-#elif defined EXTERNAL_OSCILLATOR
+#else
     // set up the oscillators
     // use external oscillator (16 MHz), enable 3x PLL (48 MHz)
     RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
@@ -176,8 +174,6 @@ void SystemClock_Config(void)
     PeriphClkInit.PeriphClockSelection = RCC_PERIPHCLK_USB;
     PeriphClkInit.UsbClockSelection = RCC_USBCLKSOURCE_PLLCLK;
 
-#else
-	#error "Please define whether to use an internal or external oscillator"
 #endif
 
     HAL_RCC_OscConfig(&RCC_OscInitStruct);
@@ -185,10 +181,42 @@ void SystemClock_Config(void)
     HAL_RCCEx_PeriphCLKConfig(&PeriphClkInit);
     __SYSCFG_CLK_ENABLE();
 
+
 	HAL_SYSTICK_Config(HAL_RCC_GetHCLKFreq()/1000);
 	HAL_SYSTICK_CLKSourceConfig(SYSTICK_CLKSOURCE_HCLK);
     HAL_NVIC_SetPriority(SysTick_IRQn, 0, 0);
 
+
+#ifdef INTERNAL_OSCILLATOR
+    // Enable clock recovery system for internal oscillator
+    RCC_CRSInitTypeDef RCC_CRSInitStruct;
+
+    // Enable CRS Clock
+    __CRS_CLK_ENABLE();
+
+    // Default Synchro Signal division factor (not divided) 
+    RCC_CRSInitStruct.Prescaler = RCC_CRS_SYNC_DIV1;
+
+    // Set the SYNCSRC[1:0] bits according to CRS_Source value 
+    RCC_CRSInitStruct.Source = RCC_CRS_SYNC_SOURCE_USB;
+
+    // HSI48 is synchronized with USB SOF at 1KHz rate 
+    RCC_CRSInitStruct.ReloadValue = __HAL_RCC_CRS_CALCULATE_RELOADVALUE(48000000, 1000);
+    RCC_CRSInitStruct.ErrorLimitValue = RCC_CRS_ERRORLIMIT_DEFAULT;
+
+    // Set the TRIM[5:0] to the default value
+    RCC_CRSInitStruct.HSI48CalibrationValue = 0x20; 
+
+    // Start automatic synchronization 
+    HAL_RCCEx_CRSConfig(&RCC_CRSInitStruct);
+
+    // Force sync event
+    HAL_RCCEx_CRSSoftwareSynchronizationGenerate();
+
+    // Wait until synchronized
+    HAL_RCCEx_CRSWaitSynchronization(3000);
+#endif
+
 }
 
 /** Configure pins as