add software filter for RPM

- define maximum value for RPM to 3600 (maximum value according to datasheet)
- monimod sends previous RPM value if the new value is > 3600 RPMs
- if reads more that 25 times a wrong value, sends a dead word (0x3A00, equivalent to 65536 RPMs)

Resolves: #13

main_fw/src/main.c

@@ -52,8 +52,15 @@ static uint16_t iter __xMR;
 static uint16_t fan_ramp_up_count __xMR = 0;
 #endif
 
+/* MAX Speed Datasheet: 3600 */
+#define FAN_MAX_RPMS 3600
+#define FAN_MAX_FAIL_CNT 25
+/* The equivalent to float is 65536.0 */
+#define FAN_DEAD_WORD 0x3A00
 static volatile uint16_t tacho_cnt[3] __xMR;
 static volatile uint16_t tacho_rpm[3] __xMR;
+static volatile uint16_t tacho_rpm_prev[3] __xMR;
+static volatile uint16_t tacho_rpm_fail_cnt[3] __xMR;
 
 // when fan_cmdrpm is 0, setfrpms and temp_curve_points_y represent
 // duty cycle (0 to 1000)
@@ -230,30 +237,69 @@ int16_t sign(int16_t x)
 void __xMR update_rpm()
 {
         // 2 sensor periods = 1 revolution
+        /* FAN 0 Control */
         if (fan_installed[0]) {
                 tacho_rpm[0] = 60*tacho_cnt[0]/(1+fan_ppr[0]);
                 tacho_cnt[0] = 0;
-                frpms_lin[0] = float_to_linear(tacho_rpm[0]);
+                if (tacho_rpm[0] <= FAN_MAX_RPMS) {
+                        frpms_lin[0] = float_to_linear(tacho_rpm[0]);
+                        tacho_rpm_prev[0] = tacho_rpm[0];
+                        tacho_rpm_fail_cnt[0] = 0;
+                } else {
+                        tacho_rpm_fail_cnt[0]++;
+                        if (tacho_rpm_fail_cnt[0] >= FAN_MAX_FAIL_CNT) {
+                                frpms_lin[0] = FAN_DEAD_WORD;
+                        } else {
+                                frpms_lin[0] = float_to_linear(tacho_rpm_prev[0]);
+                        }
+                        tacho_rpm[0] = tacho_rpm_prev[0];
+                }
         } else {
                 tacho_rpm[0] = 0;
                 tacho_cnt[0] = 0;
                 frpms_lin[0] = float_to_linear(0);
         }
 
+        /* FAN 1 Control */
         if (fan_installed[1]) {
                 tacho_rpm[1] = 60*tacho_cnt[1]/(1+fan_ppr[1]);
                 tacho_cnt[1] = 0;
-                frpms_lin[1] = float_to_linear(tacho_rpm[1]);
+                if (tacho_rpm[1] <= FAN_MAX_RPMS) {
+                        frpms_lin[1] = float_to_linear(tacho_rpm[1]);
+                        tacho_rpm_prev[1] = tacho_rpm[1];
+                        tacho_rpm_fail_cnt[1] = 0;
+                } else {
+                        tacho_rpm_fail_cnt[1]++;
+                        if (tacho_rpm_fail_cnt[1] >= FAN_MAX_FAIL_CNT) {
+                                frpms_lin[1] = FAN_DEAD_WORD;
+                        } else {
+                                frpms_lin[1] = float_to_linear(tacho_rpm_prev[1]);
+                        }
+                        tacho_rpm[1] = tacho_rpm_prev[1];
+                }
         } else {
                 tacho_rpm[1] = 0;
                 tacho_cnt[1] = 0;
                 frpms_lin[1] = float_to_linear(0);
         }
 
+        /* FAN 2 Control */
         if (fan_installed[2]) {
                 tacho_rpm[2] = 60*tacho_cnt[2]/(1+fan_ppr[2]);
                 tacho_cnt[2] = 0;
-                frpms_lin[2] = float_to_linear(tacho_rpm[2]);
+                if (tacho_rpm[2] <= FAN_MAX_RPMS) {
+                        frpms_lin[2] = float_to_linear(tacho_rpm[2]);
+                        tacho_rpm_prev[2] = tacho_rpm[2];
+                        tacho_rpm_fail_cnt[2] = 0;
+                } else {
+                        tacho_rpm_fail_cnt[2]++;
+                        if (tacho_rpm_fail_cnt[2] >= FAN_MAX_FAIL_CNT) {
+                                frpms_lin[2] = FAN_DEAD_WORD;
+                        } else {
+                                frpms_lin[2] = float_to_linear(tacho_rpm_prev[2]);
+                        }
+                        tacho_rpm[2] = tacho_rpm_prev[2];
+                }
         } else {
                 tacho_rpm[2] = 0;
                 tacho_cnt[2] = 0;
@@ -578,12 +624,18 @@ endless_loop(void)
 
 int main(void)
 {
+
 	/* Initializes MCU, drivers and middleware */
 	atmel_start_init();
         gpio_set_pin_pull_mode(ADDR0, GPIO_PULL_UP);
         gpio_set_pin_pull_mode(ADDR1, GPIO_PULL_UP);
         gpio_set_pin_pull_mode(ADDR2, GPIO_PULL_UP);
 
+        /* initialize counters to 0 */
+        tacho_rpm_fail_cnt[0] = 0;
+        tacho_rpm_fail_cnt[1] = 0;
+        tacho_rpm_fail_cnt[2] = 0;
+
 #if defined(MMFANT) || defined(MMPROT)
         ext_irq_register(PIN_PA17, inc_tacho1);
         ext_irq_register(PIN_PA16, inc_tacho2);
@@ -592,6 +644,11 @@ int main(void)
         ext_irq_enable(PIN_PA16);
         ext_irq_enable(PIN_PA13);
 
+        /* initialize previous value to 0 */
+        tacho_rpm_prev[0] = 0;
+        tacho_rpm_prev[1] = 0;
+        tacho_rpm_prev[2] = 0;
+
         load_fan_config();
 
         update_pwm();
@@ -599,6 +656,12 @@ int main(void)
 	pwm_enable(&PWM_1);
 	pwm_enable(&PWM_2);
 #else
+        /* initialize previous value to 0 */
+        tacho_rpm_prev[0] = 0;
+        tacho_rpm_prev[1] = 0;
+        tacho_rpm_prev[2] = 0;
+
+        /* RPM always 0 */
         frpms_lin[0] = float_to_linear(0);
         frpms_lin[1] = float_to_linear(0);
         frpms_lin[2] = float_to_linear(0);