Input capture works. off by *2

Software/Core/Src/main.c

@@ -58,6 +58,8 @@ static uint8_t  dio_values[NUM_DIO_PINS];
 TIM_HandleTypeDef* PWM_TIM_MAP[3] = {&htim1, &htim4, &htim3};
 
 static uint8_t  pwm_ch_active[8];
+
+static uint16_t wss_flanks[2];
 /* USER CODE END PV */
 
 /* Private function prototypes -----------------------------------------------*/
@@ -164,6 +166,10 @@ int main(void)
   // Init all channels as stopped
   memset(pwm_ch_active, 0, 8);
 
+  // Start input capture for WSS
+  HAL_TIM_IC_Start_IT(&htim8, TIM_CHANNEL_1);
+  HAL_TIM_IC_Start_IT(&htim8, TIM_CHANNEL_2);
+
   /* USER CODE END 2 */
 
   /* Infinite loop */
@@ -207,7 +213,8 @@ int main(void)
               break;
 
             case FIN:
-              /* NYI */
+              value = wss_flanks[signal->channel];
+              wss_flanks[signal->channel] = 0;
               break;
 
             default:
@@ -319,6 +326,45 @@ void HAL_ADC_ConvCpltCallback(ADC_HandleTypeDef* hadc)
   }
 }
 
+/*
+ * Input capture timing calculations:
+ * wheel speed = 8000 rpm * (11/48) = 30.55 rot/s
+ * if both flanks then 64 flanks per rot = 1956 flanks/s
+ * That's ~500µs per flank or ~1ms per notch
+ *
+ * TIM8 trigger prescaled = 96MHz/64 = 3MHz
+ * Max Filter is 15 samples, at 666.666ns per sample
+ * that's 10µs of filtering (flanks that are unstable
+ * for this long will not trigger a capture interrupt)
+ *
+ * If we want to do further filtering, we can either
+ * increase the prescaler and decrease the counter
+ * period or do it in software using
+ * HAL_TIM_ReadCapturedValue(&htim8, TIM_CHANNEL_X);
+ * to measure the time between events.
+ */
+
+void HAL_TIM_IC_CaptureCallback(TIM_HandleTypeDef *htim) {
+
+  if (htim != &htim8 || htim->Channel < 1 || htim->Channel > 2)
+    return;
+
+  /*
+   * Channels go 1,2,4,8... so we count the trailing zeros to get the index.
+   * For this, we could use the nifty CTZ instruction, which gives us exactly that.
+   * BUT according to godbolt we save 2 instructions by using subtraction,
+   * which we can only do because we only use the first two channels.
+   * Why 2 instructions? well, one because -1 can be done in the immediate when
+   * writing to memory. Another one because ARMv7 32bit doesn't have CTZ but only
+   * CLZ, so it must do RBIT before to reverse the result.
+   *
+   * CAREFUL: When using more than 2 channels, you MUST use CTZ instead.
+   */
+  wss_flanks[htim->Channel-1]++;
+  //wss_flanks[__builtin_ctz(htim->Channel)]++;
+
+}
+
 void SetCCR(TIM_TypeDef* Instance, unsigned int ch, uint8_t dc) {
   (&(Instance->CCR1))[ch] = dc;
 }