Working SysTick, code factoring, some boot-up code.

1 files changed, 50 insertions, 0 deletions

diff --git a/stm/systick.c b/stm/systick.c
new file mode 100644
index 000000000..172b75404
--- /dev/null
+++ b/stm/systick.c
@@ -0,0 +1,50 @@
+#include <stm32f4xx.h>
+#include "misc.h"
+#include "systick.h"
+
+volatile uint32_t sys_tick_counter;
+
+void sys_tick_init() {
+    // sys-tick interrupt called at 1ms intervals
+    sys_tick_counter = 0;
+    SysTick_Config(SystemCoreClock / 1000);
+}
+
+// called on SysTick interrupt
+void SysTick_Handler() {
+    sys_tick_counter++;
+}
+
+void sys_tick_delay_ms(uint32_t delay_ms) {
+    sys_tick_wait_at_least(sys_tick_counter, delay_ms);
+}
+
+// waits until at least delay_ms milliseconds have passed from the sampling of sys_tick_counter in stc
+// handles overflow properl
+// assumes stc was taken from sys_tick_counter some time before calling this function
+// eg stc <= sys_tick_counter for the case of no wrap around of sys_tick_counter
+void sys_tick_wait_at_least(uint32_t stc, uint32_t delay_ms) {
+    // stc_wait is the value of sys_tick_counter that we wait for
+    uint32_t stc_wait = stc + delay_ms;
+    if (stc_wait < stc) {
+        // stc_wait wrapped around
+        while (stc <= sys_tick_counter || sys_tick_counter < stc_wait) {
+        }
+    } else {
+        // stc_wait did not wrap around
+        while (stc <= sys_tick_counter && sys_tick_counter < stc_wait) {
+        }
+    }
+}
+
+bool sys_tick_has_passed(uint32_t stc, uint32_t delay_ms) {
+    // stc_wait is the value of sys_tick_counter that we wait for
+    uint32_t stc_wait = stc + delay_ms;
+    if (stc_wait < stc) {
+        // stc_wait wrapped around
+        return !(stc <= sys_tick_counter || sys_tick_counter < stc_wait);
+    } else {
+        // stc_wait did not wrap around
+        return !(stc <= sys_tick_counter && sys_tick_counter < stc_wait);
+    }
+}