first commit

systick.c

@@ -0,0 +1,21 @@
+#include "systick.h"
+
+volatile uint32_t systick_millis;
+
+void systick_init(void) {
+  SysTick->CTLR = 0x0000;
+  SysTick->CMP = SysTick->CNT + SYSTICK_ONE_MILLISECOND;
+  systick_millis = 0;
+  SysTick->CTLR = SYSTICK_CTLR_STE |   // Enable Counter
+                  SYSTICK_CTLR_STIE |  // Enable Interrupts
+                  SYSTICK_CTLR_STCLK;  // Set Clock Source to HCLK/1
+
+  NVIC_EnableIRQ(SysTick_IRQn);
+}
+
+void SysTick_Handler(void) __attribute__((interrupt));
+void SysTick_Handler(void) {
+  SysTick->CMP = SysTick->CNT + SYSTICK_ONE_MILLISECOND;
+  SysTick->SR = 0;
+  systick_millis++;
+}