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   1 /*
   2  * Copyright © 2009 Keith Packard <keithp@keithp.com>
   3  *
   4  * This program is free software; you can redistribute it and/or modify
   5  * it under the terms of the GNU General Public License as published by
   6  * the Free Software Foundation; version 2 of the License.
   7  *
   8  * This program is distributed in the hope that it will be useful, but
   9  * WITHOUT ANY WARRANTY; without even the implied warranty of
  10  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  11  * General Public License for more details.
  12  *
  13  * You should have received a copy of the GNU General Public License along
  14  * with this program; if not, write to the Free Software Foundation, Inc.,
  15  * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA.
  16  */
  17
  18 #ifndef AO_FLIGHT_TEST
  19 #include "ao.h"
  20 #endif
  21
  22 #ifndef HAS_ACCEL
  23 #error Please define HAS_ACCEL
  24 #endif
  25
  26 #ifndef HAS_GPS
  27 #error Please define HAS_GPS
  28 #endif
  29
  30 #ifndef HAS_USB
  31 #error Please define HAS_USB
  32 #endif
  33
  34 /* Main flight thread. */
  35
  36 __pdata enum ao_flight_state    ao_flight_state;        /* current flight state */
  37 __pdata uint16_t                ao_flight_tick;         /* time of last data */
  38 __pdata uint16_t                ao_flight_prev_tick;    /* time of previous data */
  39 __xdata int16_t                 ao_ground_pres;         /* startup pressure */
  40 __pdata uint16_t                ao_launch_tick;         /* time of launch detect */
  41 #if HAS_ACCEL
  42 __pdata int16_t                 ao_ground_accel;        /* startup acceleration */
  43 #endif
  44
  45 /*
  46  * track min/max data over a long interval to detect
  47  * resting
  48  */
  49 __pdata uint16_t                ao_interval_end;
  50 __pdata int16_t                 ao_interval_min_height;
  51 __pdata int16_t                 ao_interval_max_height;
  52
  53 __data uint8_t ao_flight_adc;
  54 __pdata int16_t ao_raw_pres;
  55 __xdata uint8_t ao_flight_force_idle;
  56
  57 #if HAS_ACCEL
  58 __pdata int16_t ao_raw_accel, ao_raw_accel_prev;
  59 __pdata int16_t ao_accel_2g;
  60
  61 /* Accelerometer calibration
  62  *
  63  * We're sampling the accelerometer through a resistor divider which
  64  * consists of 5k and 10k resistors. This multiplies the values by 2/3.
  65  * That goes into the cc1111 A/D converter, which is running at 11 bits
  66  * of precision with the bits in the MSB of the 16 bit value. Only positive
  67  * values are used, so values should range from 0-32752 for 0-3.3V. The
  68  * specs say we should see 40mV/g (uncalibrated), multiply by 2/3 for what
  69  * the A/D converter sees (26.67 mV/g). We should see 32752/3300 counts/mV,
  70  * for a final computation of:
  71  *
  72  * 26.67 mV/g * 32767/3300 counts/mV = 264.8 counts/g
  73  *
  74  * Zero g was measured at 16000 (we would expect 16384).
  75  * Note that this value is only require to tell if the
  76  * rocket is standing upright. Once that is determined,
  77  * the value of the accelerometer is averaged for 100 samples
  78  * to find the resting accelerometer value, which is used
  79  * for all further flight computations
  80  */
  81
  82 #define GRAVITY 9.80665
  83
  84 #define ACCEL_NOSE_UP   (ao_accel_2g >> 2)
  85
  86 #endif
  87
  88 /*
  89  * Barometer calibration
  90  *
  91  * We directly sample the barometer. The specs say:
  92  *
  93  * Pressure range: 15-115 kPa
  94  * Voltage at 115kPa: 2.82
  95  * Output scale: 27mV/kPa
  96  *
  97  * If we want to detect launch with the barometer, we need
  98  * a large enough bump to not be fooled by noise. At typical
  99  * launch elevations (0-2000m), a 200Pa pressure change cooresponds
 100  * to about a 20m elevation change. This is 5.4mV, or about 3LSB.
 101  * As all of our calculations are done in 16 bits, we'll actually see a change
 102  * of 16 times this though
 103  *
 104  * 27 mV/kPa * 32767 / 3300 counts/mV = 268.1 counts/kPa
 105  */
 106
 107 /* We also have a clock, which can be used to sanity check things in
 108  * case of other failures
 109  */
 110
 111 #define BOOST_TICKS_MAX AO_SEC_TO_TICKS(15)
 112
 113 #define to_fix16(x) ((int16_t) ((x) * 65536.0 + 0.5))
 114 #define to_fix32(x) ((int32_t) ((x) * 65536.0 + 0.5))
 115 #define from_fix(x)     ((x) >> 16)
 116
 117 #include "ao_kalman.h"
 118
 119 __pdata int16_t                 ao_ground_height;
 120 __pdata int16_t                 ao_height;
 121 __pdata int16_t                 ao_speed;
 122 __pdata int16_t                 ao_accel;
 123 __pdata int16_t                 ao_max_height;
 124
 125 static __pdata int32_t          ao_k_height;
 126 static __pdata int32_t          ao_k_speed;
 127 static __pdata int32_t          ao_k_accel;
 128
 129 #define AO_K_STEP_100           to_fix16(0.01)
 130 #define AO_K_STEP_2_2_100       to_fix16(0.00005)
 131
 132 #define AO_K_STEP_10            to_fix16(0.1)
 133 #define AO_K_STEP_2_2_10        to_fix16(0.005)
 134
 135 /*
 136  * Above this height, the baro sensor doesn't work
 137  */
 138 #define AO_MAX_BARO_HEIGHT      8000
 139
 140 /*
 141  * Above this speed, baro measurements are unreliable
 142  */
 143 #define AO_MAX_BARO_SPEED       300
 144
 145 static void
 146 ao_kalman_predict(void)
 147 {
 148 #ifdef AO_FLIGHT_TEST
 149         if (ao_flight_tick - ao_flight_prev_tick > 5) {
 150                 ao_k_height += ((int32_t) ao_speed * AO_K_STEP_10 +
 151                                 (int32_t) ao_accel * AO_K_STEP_2_2_10) >> 4;
 152                 ao_k_speed += (int32_t) ao_accel * AO_K_STEP_10;
 153
 154                 return;
 155         }
 156 #endif
 157         ao_k_height += ((int32_t) ao_speed * AO_K_STEP_100 +
 158                         (int32_t) ao_accel * AO_K_STEP_2_2_100) >> 4;
 159         ao_k_speed += (int32_t) ao_accel * AO_K_STEP_100;
 160 }
 161
 162 static __pdata int16_t ao_error_h;
 163 static __pdata int16_t ao_raw_alt;
 164 static __pdata int16_t ao_raw_height;
 165 static __pdata int16_t ao_error_h_sq_avg;
 166
 167 static void
 168 ao_kalman_err_height(void)
 169 {
 170         int16_t e;
 171         ao_error_h = ao_raw_height - (int16_t) (ao_k_height >> 16);
 172
 173         e = ao_error_h;
 174         if (e < 0)
 175                 e = -e;
 176         if (e > 127)
 177                 e = 127;
 178         ao_error_h_sq_avg -= ao_error_h_sq_avg >> 4;
 179         ao_error_h_sq_avg += (e * e) >> 4;
 180 }
 181
 182 static void
 183 ao_kalman_correct_baro(void)
 184 {
 185         ao_kalman_err_height();
 186 #ifdef AO_FLIGHT_TEST
 187         if (ao_flight_tick - ao_flight_prev_tick > 5) {
 188                 ao_k_height += (int32_t) AO_BARO_K0_10 * ao_error_h;
 189                 ao_k_speed  += (int32_t) AO_BARO_K1_10 * ao_error_h;
 190                 ao_k_accel  += (int32_t) AO_BARO_K2_10 * ao_error_h;
 191                 return;
 192         }
 193 #endif
 194         ao_k_height += (int32_t) AO_BARO_K0_100 * ao_error_h;
 195         ao_k_speed  += (int32_t) AO_BARO_K1_100 * ao_error_h;
 196         ao_k_accel  += (int32_t) AO_BARO_K2_100 * ao_error_h;
 197 }
 198
 199 #if HAS_ACCEL
 200 static __pdata int16_t ao_error_a;
 201 static __pdata int32_t ao_accel_scale;
 202
 203 static void
 204 ao_kalman_err_accel(void)
 205 {
 206         int32_t accel;
 207
 208         accel = (ao_ground_accel - ao_raw_accel) * ao_accel_scale;
 209
 210         /* Can't use ao_accel here as it is the pre-prediction value still */
 211         ao_error_a = (accel - ao_k_accel) >> 16;
 212 }
 213
 214 static void
 215 ao_kalman_correct_both(void)
 216 {
 217         ao_kalman_err_height();
 218         ao_kalman_err_accel();
 219
 220 #if 0
 221         /*
 222          * Check to see if things are crazy here --
 223          * if the computed height is far above the
 224          * measured height, we assume that the flight
 225          * trajectory is not vertical, and so ignore
 226          * the accelerometer for the remainder of the
 227          * flight.
 228          */
 229         if (ao_error_h_sq_avg > 10)
 230         {
 231                 ao_kalman_correct_baro();
 232                 return;
 233         }
 234 #endif
 235
 236 #ifdef AO_FLIGHT_TEST
 237         if (ao_flight_tick - ao_flight_prev_tick > 5) {
 238                 ao_k_height +=
 239                         (int32_t) AO_BOTH_K00_10 * ao_error_h +
 240                         (int32_t) (AO_BOTH_K01_10 >> 4) * ao_error_a;
 241                 ao_k_speed +=
 242                         ((int32_t) AO_BOTH_K10_10 << 4) * ao_error_h +
 243                         (int32_t) AO_BOTH_K11_10 * ao_error_a;
 244                 ao_k_accel +=
 245                         ((int32_t) AO_BOTH_K20_10 << 4) * ao_error_h +
 246                         (int32_t) AO_BOTH_K21_10 * ao_error_a;
 247                 return;
 248         }
 249 #endif
 250         ao_k_height +=
 251                 (int32_t) AO_BOTH_K00_100 * ao_error_h +
 252                 (int32_t) AO_BOTH_K01_100 * ao_error_a;
 253         ao_k_speed +=
 254                 (int32_t) AO_BOTH_K10_100 * ao_error_h +
 255                 (int32_t) AO_BOTH_K11_100 * ao_error_a;
 256         ao_k_accel +=
 257                 (int32_t) AO_BOTH_K20_100 * ao_error_h +
 258                 (int32_t) AO_BOTH_K21_100 * ao_error_a;
 259 }
 260
 261 static void
 262 ao_kalman_correct_accel(void)
 263 {
 264         ao_kalman_err_accel();
 265
 266 #ifdef AO_FLIGHT_TEST
 267         if (ao_flight_tick - ao_flight_prev_tick > 5) {
 268                 ao_k_height +=(int32_t) AO_ACCEL_K0_10 * ao_error_a;
 269                 ao_k_speed  += (int32_t) AO_ACCEL_K1_10 * ao_error_a;
 270                 ao_k_accel  += (int32_t) AO_ACCEL_K2_10 * ao_error_a;
 271                 return;
 272         }
 273 #endif
 274         ao_k_height += (int32_t) AO_ACCEL_K0_100 * ao_error_a;
 275         ao_k_speed  += (int32_t) AO_ACCEL_K1_100 * ao_error_a;
 276         ao_k_accel  += (int32_t) AO_ACCEL_K2_100 * ao_error_a;
 277 }
 278 #endif /* HAS_ACCEL */
 279
 280 __xdata int32_t ao_raw_pres_sum;
 281
 282 #ifdef HAS_ACCEL
 283 __xdata int32_t ao_raw_accel_sum;
 284 #endif
 285
 286 /* Landing is detected by getting constant readings from both pressure and accelerometer
 287  * for a fairly long time (AO_INTERVAL_TICKS)
 288  */
 289 #define AO_INTERVAL_TICKS       AO_SEC_TO_TICKS(5)
 290
 291 #define abs(a)  ((a) < 0 ? -(a) : (a))
 292
 293 void
 294 ao_flight(void)
 295 {
 296         __pdata static uint16_t nsamples = 0;
 297
 298         ao_flight_adc = ao_adc_head;
 299         ao_raw_pres = 0;
 300 #if HAS_ACCEL
 301         ao_raw_accel_prev = 0;
 302         ao_raw_accel = 0;
 303 #endif
 304         ao_flight_tick = 0;
 305         for (;;) {
 306                 ao_wakeup(DATA_TO_XDATA(&ao_flight_adc));
 307                 ao_sleep(DATA_TO_XDATA(&ao_adc_head));
 308                 while (ao_flight_adc != ao_adc_head) {
 309                         __xdata struct ao_adc *ao_adc;
 310                         ao_flight_prev_tick = ao_flight_tick;
 311
 312                         /* Capture a sample */
 313                         ao_adc = &ao_adc_ring[ao_flight_adc];
 314                         ao_flight_tick = ao_adc->tick;
 315                         ao_raw_pres = ao_adc->pres;
 316                         ao_raw_alt = ao_pres_to_altitude(ao_raw_pres);
 317                         ao_raw_height = ao_raw_alt - ao_ground_height;
 318 #if HAS_ACCEL
 319                         ao_raw_accel = ao_adc->accel;
 320 #if HAS_ACCEL_REF
 321                         /*
 322                          * Ok, the math here is a bit tricky.
 323                          *
 324                          * ao_raw_accel:  ADC output for acceleration
 325                          * ao_accel_ref:  ADC output for the 5V reference.
 326                          * ao_cook_accel: Corrected acceleration value
 327                          * Vcc:           3.3V supply to the CC1111
 328                          * Vac:           5V supply to the accelerometer
 329                          * accel:         input voltage to accelerometer ADC pin
 330                          * ref:           input voltage to 5V reference ADC pin
 331                          *
 332                          *
 333                          * Measured acceleration is ratiometric to Vcc:
 334                          *
 335                          *     ao_raw_accel   accel
 336                          *     ------------ = -----
 337                          *        32767        Vcc
 338                          *
 339                          * Measured 5v reference is also ratiometric to Vcc:
 340                          *
 341                          *     ao_accel_ref    ref
 342                          *     ------------ = -----
 343                          *        32767        Vcc
 344                          *
 345                          *
 346                          *      ao_accel_ref = 32767 * (ref / Vcc)
 347                          *
 348                          * Acceleration is measured ratiometric to the 5V supply,
 349                          * so what we want is:
 350                          *
 351                          *      ao_cook_accel    accel
 352                          *      ------------- =  -----
 353                          *          32767         ref
 354                          *
 355                          *
 356                          *                      accel    Vcc
 357                          *                    = ----- *  ---
 358                          *                       Vcc     ref
 359                          *
 360                          *                      ao_raw_accel       32767
 361                          *                    = ------------ *  ------------
 362                          *                         32737        ao_accel_ref
 363                          *
 364                          * Multiply through by 32767:
 365                          *
 366                          *                      ao_raw_accel * 32767
 367                          *      ao_cook_accel = --------------------
 368                          *                          ao_accel_ref
 369                          *
 370                          * Now, the tricky part. Getting this to compile efficiently
 371                          * and keeping all of the values in-range.
 372                          *
 373                          * First off, we need to use a shift of 16 instead of * 32767 as SDCC
 374                          * does the obvious optimizations for byte-granularity shifts:
 375                          *
 376                          *      ao_cook_accel = (ao_raw_accel << 16) / ao_accel_ref
 377                          *
 378                          * Next, lets check our input ranges:
 379                          *
 380                          *      0 <= ao_raw_accel <= 0x7fff             (singled ended ADC conversion)
 381                          *      0x7000 <= ao_accel_ref <= 0x7fff        (the 5V ref value is close to 0x7fff)
 382                          *
 383                          * Plugging in our input ranges, we get an output range of 0 - 0x12490,
 384                          * which is 17 bits. That won't work. If we take the accel ref and shift
 385                          * by a bit, we'll change its range:
 386                          *
 387                          *      0xe000 <= ao_accel_ref<<1 <= 0xfffe
 388                          *
 389                          *      ao_cook_accel = (ao_raw_accel << 16) / (ao_accel_ref << 1)
 390                          *
 391                          * Now the output range is 0 - 0x9248, which nicely fits in 16 bits. It
 392                          * is, however, one bit too large for our signed computations. So, we
 393                          * take the result and shift that by a bit:
 394                          *
 395                          *      ao_cook_accel = ((ao_raw_accel << 16) / (ao_accel_ref << 1)) >> 1
 396                          *
 397                          * This finally creates an output range of 0 - 0x4924. As the ADC only
 398                          * provides 11 bits of data, we haven't actually lost any precision,
 399                          * just dropped a bit of noise off the low end.
 400                          */
 401                         ao_raw_accel = (uint16_t) ((((uint32_t) ao_raw_accel << 16) / (ao_accel_ref[ao_flight_adc] << 1))) >> 1;
 402                         ao_adc->accel = ao_raw_accel;
 403 #endif
 404 #endif
 405
 406                         if (ao_flight_state > ao_flight_idle) {
 407                                 ao_kalman_predict();
 408 #if HAS_ACCEL
 409                                 if (ao_flight_state <= ao_flight_coast) {
 410 #ifndef FORCE_ACCEL
 411                                         if (/*ao_speed < AO_MS_TO_SPEED(AO_MAX_BARO_SPEED) &&*/
 412                                             ao_raw_alt < AO_MAX_BARO_HEIGHT)
 413                                                 ao_kalman_correct_both();
 414                                         else
 415 #endif
 416                                                 ao_kalman_correct_accel();
 417                                 } else
 418 #endif
 419                                 if (ao_raw_alt < AO_MAX_BARO_HEIGHT || ao_flight_state >= ao_flight_drogue)
 420                                         ao_kalman_correct_baro();
 421                                 ao_height = from_fix(ao_k_height);
 422                                 ao_speed = from_fix(ao_k_speed);
 423                                 ao_accel = from_fix(ao_k_accel);
 424                                 if (ao_height > ao_max_height)
 425                                         ao_max_height = ao_height;
 426                         }
 427                         ao_flight_adc = ao_adc_ring_next(ao_flight_adc);
 428                 }
 429
 430                 switch (ao_flight_state) {
 431                 case ao_flight_startup:
 432
 433                         /* startup state:
 434                          *
 435                          * Collect 512 samples of acceleration and pressure
 436                          * data and average them to find the resting values
 437                          */
 438                         if (nsamples < 512) {
 439 #if HAS_ACCEL
 440                                 ao_raw_accel_sum += ao_raw_accel;
 441 #endif
 442                                 ao_raw_pres_sum += ao_raw_pres;
 443                                 ++nsamples;
 444                                 continue;
 445                         }
 446                         ao_config_get();
 447 #if HAS_ACCEL
 448                         ao_ground_accel = ao_raw_accel_sum >> 9;
 449                         ao_accel_2g = ao_config.accel_minus_g - ao_config.accel_plus_g;
 450                         ao_accel_scale = to_fix32(GRAVITY * 2 * 16) / ao_accel_2g;
 451 #endif
 452                         ao_ground_pres = ao_raw_pres_sum >> 9;
 453                         ao_ground_height = ao_pres_to_altitude(ao_ground_pres);
 454
 455                         /* Check to see what mode we should go to.
 456                          *  - Invalid mode if accel cal appears to be out
 457                          *  - pad mode if we're upright,
 458                          *  - idle mode otherwise
 459                          */
 460 #if HAS_ACCEL
 461                         if (ao_config.accel_plus_g == 0 ||
 462                             ao_config.accel_minus_g == 0 ||
 463                             ao_ground_accel < ao_config.accel_plus_g - ACCEL_NOSE_UP ||
 464                             ao_ground_accel > ao_config.accel_minus_g + ACCEL_NOSE_UP)
 465                         {
 466                                 /* Detected an accel value outside -1.5g to 1.5g
 467                                  * (or uncalibrated values), so we go into invalid mode
 468                                  */
 469                                 ao_flight_state = ao_flight_invalid;
 470
 471                         } else
 472 #endif
 473                                 if (!ao_flight_force_idle
 474 #if HAS_ACCEL
 475                                     && ao_ground_accel < ao_config.accel_plus_g + ACCEL_NOSE_UP
 476 #endif
 477                                         )
 478                         {
 479                                 /* Set pad mode - we can fly! */
 480                                 ao_flight_state = ao_flight_pad;
 481 #if HAS_USB
 482                                 /* Disable the USB controller in flight mode
 483                                  * to save power
 484                                  */
 485                                 ao_usb_disable();
 486 #endif
 487
 488                                 /* Disable packet mode in pad state */
 489                                 ao_packet_slave_stop();
 490
 491                                 /* Turn on telemetry system */
 492                                 ao_rdf_set(1);
 493                                 ao_telemetry_set_interval(AO_TELEMETRY_INTERVAL_PAD);
 494
 495                                 /* signal successful initialization by turning off the LED */
 496                                 ao_led_off(AO_LED_RED);
 497                         } else {
 498                                 /* Set idle mode */
 499                                 ao_flight_state = ao_flight_idle;
 500
 501                                 /* signal successful initialization by turning off the LED */
 502                                 ao_led_off(AO_LED_RED);
 503                         }
 504                         /* wakeup threads due to state change */
 505                         ao_wakeup(DATA_TO_XDATA(&ao_flight_state));
 506
 507                         break;
 508                 case ao_flight_pad:
 509
 510                         /* pad to boost:
 511                          *
 512                          * barometer: > 20m vertical motion
 513                          *             OR
 514                          * accelerometer: > 2g AND velocity > 5m/s
 515                          *
 516                          * The accelerometer should always detect motion before
 517                          * the barometer, but we use both to make sure this
 518                          * transition is detected. If the device
 519                          * doesn't have an accelerometer, then ignore the
 520                          * speed and acceleration as they are quite noisy
 521                          * on the pad.
 522                          */
 523                         if (ao_height > AO_M_TO_HEIGHT(20)
 524 #if HAS_ACCEL
 525                             || (ao_accel > AO_MSS_TO_ACCEL(20) &&
 526                                 ao_speed > AO_MS_TO_SPEED(5))
 527 #endif
 528                                 )
 529                         {
 530                                 ao_flight_state = ao_flight_boost;
 531                                 ao_launch_tick = ao_flight_tick;
 532
 533                                 /* start logging data */
 534                                 ao_log_start();
 535
 536                                 /* Increase telemetry rate */
 537                                 ao_telemetry_set_interval(AO_TELEMETRY_INTERVAL_FLIGHT);
 538
 539                                 /* disable RDF beacon */
 540                                 ao_rdf_set(0);
 541
 542 #if HAS_GPS
 543                                 /* Record current GPS position by waking up GPS log tasks */
 544                                 ao_wakeup(&ao_gps_data);
 545                                 ao_wakeup(&ao_gps_tracking_data);
 546 #endif
 547
 548                                 ao_wakeup(DATA_TO_XDATA(&ao_flight_state));
 549                                 break;
 550                         }
 551                         break;
 552                 case ao_flight_boost:
 553
 554                         /* boost to fast:
 555                          *
 556                          * accelerometer: start to fall at > 1/4 G
 557                          *              OR
 558                          * time: boost for more than 15 seconds
 559                          *
 560                          * Detects motor burn out by the switch from acceleration to
 561                          * deceleration, or by waiting until the maximum burn duration
 562                          * (15 seconds) has past.
 563                          */
 564                         if ((ao_accel < AO_MSS_TO_ACCEL(-2.5) && ao_height > AO_M_TO_HEIGHT(100)) ||
 565                             (int16_t) (ao_flight_tick - ao_launch_tick) > BOOST_TICKS_MAX)
 566                         {
 567                                 ao_flight_state = ao_flight_fast;
 568                                 ao_wakeup(DATA_TO_XDATA(&ao_flight_state));
 569                                 break;
 570                         }
 571                         break;
 572                 case ao_flight_fast:
 573                         /*
 574                          * This is essentially the same as coast,
 575                          * but the barometer is being ignored as
 576                          * it may be unreliable.
 577                          */
 578                         if (ao_speed < AO_MS_TO_SPEED(AO_MAX_BARO_SPEED)) {
 579                                 ao_flight_state = ao_flight_coast;
 580                                 ao_wakeup(DATA_TO_XDATA(&ao_flight_state));
 581                                 break;
 582                         }
 583                         break;
 584                 case ao_flight_coast:
 585
 586                         /* apogee detect: coast to drogue deploy:
 587                          *
 588                          * speed: < 0
 589                          *
 590                          * Also make sure the model altitude is tracking
 591                          * the measured altitude reasonably closely; otherwise
 592                          * we're probably transsonic.
 593                          */
 594                         if (ao_speed < 0 && (ao_raw_alt >= AO_MAX_BARO_HEIGHT || ao_error_h_sq_avg < 100))
 595                         {
 596                                 /* ignite the drogue charge */
 597                                 ao_ignite(ao_igniter_drogue);
 598
 599                                 /* slow down the telemetry system */
 600                                 ao_telemetry_set_interval(AO_TELEMETRY_INTERVAL_RECOVER);
 601
 602                                 /*
 603                                  * Start recording min/max height
 604                                  * to figure out when the rocket has landed
 605                                  */
 606
 607                                 /* initialize interval values */
 608                                 ao_interval_end = ao_flight_tick + AO_INTERVAL_TICKS;
 609
 610                                 ao_interval_min_height = ao_interval_max_height = ao_height;
 611
 612                                 /* and enter drogue state */
 613                                 ao_flight_state = ao_flight_drogue;
 614                                 ao_wakeup(DATA_TO_XDATA(&ao_flight_state));
 615                         }
 616
 617                         break;
 618                 case ao_flight_drogue:
 619
 620                         /* drogue to main deploy:
 621                          *
 622                          * barometer: reach main deploy altitude
 623                          *
 624                          * Would like to use the accelerometer for this test, but
 625                          * the orientation of the flight computer is unknown after
 626                          * drogue deploy, so we ignore it. Could also detect
 627                          * high descent rate using the pressure sensor to
 628                          * recognize drogue deploy failure and eject the main
 629                          * at that point. Perhaps also use the drogue sense lines
 630                          * to notice continutity?
 631                          */
 632                         if (ao_height <= ao_config.main_deploy)
 633                         {
 634                                 ao_ignite(ao_igniter_main);
 635                                 ao_flight_state = ao_flight_main;
 636                                 ao_wakeup(DATA_TO_XDATA(&ao_flight_state));
 637                         }
 638
 639                         /* fall through... */
 640                 case ao_flight_main:
 641
 642                         /* drogue/main to land:
 643                          *
 644                          * barometer: altitude stable and within 1000m of the launch altitude
 645                          */
 646
 647                         if (ao_height < ao_interval_min_height)
 648                                 ao_interval_min_height = ao_height;
 649                         if (ao_height > ao_interval_max_height)
 650                                 ao_interval_max_height = ao_height;
 651
 652                         if ((int16_t) (ao_flight_tick - ao_interval_end) >= 0) {
 653                                 if (ao_height < AO_M_TO_HEIGHT(1000) &&
 654                                     ao_interval_max_height - ao_interval_min_height < AO_M_TO_HEIGHT(5))
 655                                 {
 656                                         ao_flight_state = ao_flight_landed;
 657
 658                                         /* turn off the ADC capture */
 659                                         ao_timer_set_adc_interval(0);
 660                                         /* Enable RDF beacon */
 661                                         ao_rdf_set(1);
 662
 663                                         ao_wakeup(DATA_TO_XDATA(&ao_flight_state));
 664                                 }
 665                                 ao_interval_min_height = ao_interval_max_height = ao_height;
 666                                 ao_interval_end = ao_flight_tick + AO_INTERVAL_TICKS;
 667                         }
 668                         break;
 669                 case ao_flight_landed:
 670                         break;
 671                 }
 672         }
 673 }
 674
 675 static __xdata struct ao_task   flight_task;
 676
 677 void
 678 ao_flight_init(void)
 679 {
 680         ao_flight_state = ao_flight_startup;
 681         ao_add_task(&flight_task, ao_flight, "flight");
 682 }