1 files changed, 66 insertions, 0 deletions
diff --git a/stm32/app/tacho.c b/stm32/app/tacho.c
new file mode 100644
index 0000000..bf0222c
--- /dev/null
+++ b/stm32/app/tacho.c
@@ -0,0 +1,66 @@
+#include "project.h"
+
+#define  SPURIOUS MS(10)        /*Anything faster than 6000rpm is a false trigger */
+
+
+
+uint32_t raw_tacho;
+
+static uint32_t
+cycle_diff (uint32_t a, uint32_t b)
+{
+  return b - a;
+}
+
+
+
+void
+TACHO_ISR (void)
+{
+  uint32_t now, diff;
+  static uint32_t last_edge;
+
+  if (! (EXTI_PR & TACHO))
+    return;
+
+  EXTI_PR = TACHO;
+
+  now = dwt_read_cycle_counter();
+
+  diff = cycle_diff (last_edge, now);
+
+  if (diff < SPURIOUS)
+    return;
+
+  last_edge = now;
+
+
+  /* Want RPM, diff is in units of 1/72 us */
+
+  if (!diff)
+    return;
+
+  /* uint32_t is un-able to express 60s in clock ticks, so divide everything by 2 */
+
+  diff >>= 1;
+
+
+
+  raw_tacho = (US ((60U * 1000000) / 2)) / diff;
+
+}
+
+
+void
+tacho_init (void)
+{
+  MAP_INPUT_PU (TACHO);
+
+  exti_select_source (TACHO, TACHO_PORT);
+  exti_set_trigger (TACHO, EXTI_TRIGGER_FALLING);
+  exti_enable_request (TACHO);
+  exti_reset_request (TACHO);
+
+  nvic_enable_irq (TACHO_IRQ);
+
+}