Avoid 16-bit overflow in velocity computation.

[fw/altos] / ao_flight.c

diff --git a/ao_flight.c b/ao_flight.c
index 0b47bfa51a8a50adcaef8a9d1c1cdc3319872437..51b2cd5eff138d8ff937f2fc3917ca4ca7aa0820 100644 (file)
--- a/ao_flight.c
+++ b/ao_flight.c
@@ -125,6 +125,8 @@ __pdata int16_t ao_raw_accel, ao_raw_accel_prev, ao_raw_pres;
  */
 __pdata int32_t        ao_flight_vel;
 __pdata int32_t ao_min_vel;
+__pdata int32_t        ao_old_vel;
+__pdata int16_t ao_old_vel_tick;
 __xdata int32_t ao_raw_accel_sum, ao_raw_pres_sum;
 
 /* Landing is detected by getting constant readings from both pressure and accelerometer
@@ -156,6 +158,10 @@ ao_flight(void)
                        ao_raw_pres = ao_adc_ring[ao_flight_adc].pres;
                        ao_flight_tick = ao_adc_ring[ao_flight_adc].tick;
 
+                       ao_flight_accel -= ao_flight_accel >> 4;
+                       ao_flight_accel += ao_raw_accel >> 4;
+                       ao_flight_pres -= ao_flight_pres >> 4;
+                       ao_flight_pres += ao_raw_pres >> 4;
                        /* Update velocity
                         *
                         * The accelerometer is mounted so that
@@ -164,7 +170,7 @@ ao_flight(void)
                         * so subtract instead of add.
                         */
                        ticks = ao_flight_tick - ao_flight_prev_tick;
-                       ao_vel_change = (((ao_raw_accel + ao_raw_accel_prev) >> 1) - ao_ground_accel);
+                       ao_vel_change = (((ao_raw_accel >> 1) + (ao_raw_accel_prev >> 1)) - ao_ground_accel);
                        ao_raw_accel_prev = ao_raw_accel;
 
                        /* one is a common interval */
@@ -175,10 +181,6 @@ ao_flight(void)
 
                        ao_flight_adc = ao_adc_ring_next(ao_flight_adc);
                }
-               ao_flight_accel -= ao_flight_accel >> 4;
-               ao_flight_accel += ao_raw_accel >> 4;
-               ao_flight_pres -= ao_flight_pres >> 4;
-               ao_flight_pres += ao_raw_pres >> 4;
 
                if (ao_flight_pres < ao_min_pres)
                        ao_min_pres = ao_flight_pres;
@@ -211,6 +213,8 @@ ao_flight(void)
                        ao_main_pres = ao_altitude_to_pres(ao_pres_to_altitude(ao_ground_pres) + ao_config.main_deploy);
                        ao_flight_vel = 0;
                        ao_min_vel = 0;
+                       ao_old_vel = ao_flight_vel;
+                       ao_old_vel_tick = ao_flight_tick;
 
                        /* Go to launchpad state if the nose is pointing up */
                        ao_config_get();
@@ -241,6 +245,16 @@ ao_flight(void)
                        break;
                case ao_flight_launchpad:
 
+                       /* Trim velocity
+                        *
+                        * Once a second, remove any velocity from
+                        * a second ago
+                        */
+                       if ((int16_t) (ao_flight_tick - ao_old_vel_tick) >= AO_SEC_TO_TICKS(1)) {
+                               ao_old_vel_tick = ao_flight_tick;
+                               ao_flight_vel -= ao_old_vel;
+                               ao_old_vel = ao_flight_vel;
+                       }
                        /* pad to boost:
                         *
                         * accelerometer: > 2g AND velocity > 5m/s
@@ -334,7 +348,7 @@ ao_flight(void)
                         * over in that case and the integrated velocity
                         * measurement should suffice to find apogee
                         */
-                       if (abs(ao_flight_vel) > ao_min_vel + ACCEL_VEL_APOGEE ||
+                       if (/* abs(ao_flight_vel) > ao_min_vel + ACCEL_VEL_APOGEE || */
                            ao_flight_pres > ao_min_pres + BARO_APOGEE)
                        {
                                /* ignite the drogue charge */