1 files changed, 46 insertions, 0 deletions
diff --git a/demos/ARMCM3-STM32F103-GCC/board.c b/demos/ARMCM3-STM32F103-GCC/board.c
index 1d689bee8..09636cb9d 100644
--- a/demos/ARMCM3-STM32F103-GCC/board.c
+++ b/demos/ARMCM3-STM32F103-GCC/board.c
@@ -22,14 +22,55 @@
 #include "board.h"
 
 /*
+ * Wait states setting is a function of the system clock. Those are the
+ * recommended values, there should not be need to change them.
+ */
+#if SYSCLK <= 24000000
+#define FLASHBITS 0x00000010
+#else
+#if SYSCLK <= 48000000
+#define FLASHBITS 0x00000011
+#else
+#define FLASHBITS 0x00000012
+#endif
+#endif
+
+/*
  * Hardware initialization goes here.
  * NOTE: Interrupts are still disabled.
  */
 void hwinit(void) {
 
   /*
+   * Clocks and PLL initialization.
+   */
+  // HSI setup.
+  RCC->CR = 0x00000083;         // Enforces a known state (HSI ON).
+  while (!(RCC->CR & (1 << 1)))
+    ;                           // Waits until HSI stable, it should already be.
+  // HSE setup.
+  RCC->CR |= (1 << 16);         // HSE ON.
+  while (!(RCC->CR & (1 << 17)))
+    ;                           // Waits until HSE stable.
+  // PLL setup.
+  RCC->CFGR |= PLLPREBITS | PLLMULBITS | PLLSRCBITS;
+  RCC->CR |= (1 << 24);         // PLL ON.
+  while (!(RCC->CR & (1 << 25)))
+    ;                           // Waits until PLL stable.
+  // Clock sources.
+  RCC->CFGR |= AHBBITS | PPRE1BITS | PPRE2BITS | ADCPREBITS |
+               USBPREBITS | MCOSRCBITS;
+
+  /*
+   * Flash setup and final clock selection.
+   */
+  FLASH->ACR = FLASHBITS;       // Flash wait states depending on clock.
+  RCC->CFGR |= SYSSRCBITS;      // Switches on the PLL clock.
+
+  /*
    * I/O ports initialization as specified in board.h.
    */
+  RCC->APB2ENR = 0x0000003D;    // Ports A-D enabled, AFIO enabled.
   GPIOA->CRL = VAL_GPIOACRL;
   GPIOA->CRH = VAL_GPIOACRH;
   GPIOA->ODR = VAL_GPIOAODR;
@@ -45,4 +86,9 @@ void hwinit(void) {
   GPIOD->CRL = VAL_GPIODCRL;
   GPIOD->CRH = VAL_GPIODCRH;
   GPIOD->ODR = VAL_GPIODODR;
+
+  /*
+   * NVIC/SCB setup.
+   */
+  SCB->AIRCR = (0x5FA << 16) | (0x5 << 8);      // PRIGROUP = 5 (2:6).
 }