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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      12000
 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         int16_t height_distrust;
 172 #if HAS_ACCEL
 173         int16_t speed_distrust;
 174 #endif
 175
 176         ao_error_h = ao_raw_height - (int16_t) (ao_k_height >> 16);
 177
 178         e = ao_error_h;
 179         if (e < 0)
 180                 e = -e;
 181         if (e > 127)
 182                 e = 127;
 183         ao_error_h_sq_avg -= ao_error_h_sq_avg >> 4;
 184         ao_error_h_sq_avg += (e * e) >> 4;
 185
 186         height_distrust = ao_raw_height - AO_MAX_BARO_HEIGHT;
 187 #if HAS_ACCEL
 188         speed_distrust = (ao_speed - AO_MS_TO_SPEED(AO_MAX_BARO_SPEED)) >> 4;
 189         if (speed_distrust <= 0)
 190                 speed_distrust = 0;
 191         else if (speed_distrust > height_distrust)
 192                 height_distrust = speed_distrust;
 193 #endif
 194         if (height_distrust <= 0)
 195                 height_distrust = 0;
 196
 197         if (height_distrust) {
 198                 if (height_distrust > 0x100)
 199                         height_distrust = 0x100;
 200                 ao_error_h = (int16_t) ((int32_t) ao_error_h * (0x100 - height_distrust)) >> 8;
 201         }
 202 }
 203
 204 static void
 205 ao_kalman_correct_baro(void)
 206 {
 207         ao_kalman_err_height();
 208 #ifdef AO_FLIGHT_TEST
 209         if (ao_flight_tick - ao_flight_prev_tick > 5) {
 210                 ao_k_height += (int32_t) AO_BARO_K0_10 * ao_error_h;
 211                 ao_k_speed  += (int32_t) AO_BARO_K1_10 * ao_error_h;
 212                 ao_k_accel  += (int32_t) AO_BARO_K2_10 * ao_error_h;
 213                 return;
 214         }
 215 #endif
 216         ao_k_height += (int32_t) AO_BARO_K0_100 * ao_error_h;
 217         ao_k_speed  += (int32_t) AO_BARO_K1_100 * ao_error_h;
 218         ao_k_accel  += (int32_t) AO_BARO_K2_100 * ao_error_h;
 219 }
 220
 221 #if HAS_ACCEL
 222 static __pdata int16_t ao_error_a;
 223 static __pdata int32_t ao_accel_scale;
 224
 225 static void
 226 ao_kalman_err_accel(void)
 227 {
 228         int32_t accel;
 229
 230         accel = (ao_ground_accel - ao_raw_accel) * ao_accel_scale;
 231
 232         /* Can't use ao_accel here as it is the pre-prediction value still */
 233         ao_error_a = (accel - ao_k_accel) >> 16;
 234 }
 235
 236 static void
 237 ao_kalman_correct_both(void)
 238 {
 239         ao_kalman_err_height();
 240         ao_kalman_err_accel();
 241
 242 #ifdef AO_FLIGHT_TEST
 243         if (ao_flight_tick - ao_flight_prev_tick > 5) {
 244                 ao_k_height +=
 245                         (int32_t) AO_BOTH_K00_10 * ao_error_h +
 246                         (int32_t) (AO_BOTH_K01_10 >> 4) * ao_error_a;
 247                 ao_k_speed +=
 248                         ((int32_t) AO_BOTH_K10_10 << 4) * ao_error_h +
 249                         (int32_t) AO_BOTH_K11_10 * ao_error_a;
 250                 ao_k_accel +=
 251                         ((int32_t) AO_BOTH_K20_10 << 4) * ao_error_h +
 252                         (int32_t) AO_BOTH_K21_10 * ao_error_a;
 253                 return;
 254         }
 255 #endif
 256         ao_k_height +=
 257                 (int32_t) AO_BOTH_K00_100 * ao_error_h +
 258                 (int32_t) AO_BOTH_K01_100 * ao_error_a;
 259         ao_k_speed +=
 260                 (int32_t) AO_BOTH_K10_100 * ao_error_h +
 261                 (int32_t) AO_BOTH_K11_100 * ao_error_a;
 262         ao_k_accel +=
 263                 (int32_t) AO_BOTH_K20_100 * ao_error_h +
 264                 (int32_t) AO_BOTH_K21_100 * ao_error_a;
 265 }
 266
 267 static void
 268 ao_kalman_correct_accel(void)
 269 {
 270         ao_kalman_err_accel();
 271
 272 #ifdef AO_FLIGHT_TEST
 273         if (ao_flight_tick - ao_flight_prev_tick > 5) {
 274                 ao_k_height +=(int32_t) AO_ACCEL_K0_10 * ao_error_a;
 275                 ao_k_speed  += (int32_t) AO_ACCEL_K1_10 * ao_error_a;
 276                 ao_k_accel  += (int32_t) AO_ACCEL_K2_10 * ao_error_a;
 277                 return;
 278         }
 279 #endif
 280         ao_k_height += (int32_t) AO_ACCEL_K0_100 * ao_error_a;
 281         ao_k_speed  += (int32_t) AO_ACCEL_K1_100 * ao_error_a;
 282         ao_k_accel  += (int32_t) AO_ACCEL_K2_100 * ao_error_a;
 283 }
 284 #endif /* HAS_ACCEL */
 285
 286 __xdata int32_t ao_raw_pres_sum;
 287
 288 #ifdef HAS_ACCEL
 289 __xdata int32_t ao_raw_accel_sum;
 290 #endif
 291
 292 /* Landing is detected by getting constant readings from both pressure and accelerometer
 293  * for a fairly long time (AO_INTERVAL_TICKS)
 294  */
 295 #define AO_INTERVAL_TICKS       AO_SEC_TO_TICKS(5)
 296
 297 #define abs(a)  ((a) < 0 ? -(a) : (a))
 298
 299 void
 300 ao_flight(void)
 301 {
 302         __pdata static uint16_t nsamples = 0;
 303
 304         ao_flight_adc = ao_adc_head;
 305         ao_raw_pres = 0;
 306 #if HAS_ACCEL
 307         ao_raw_accel_prev = 0;
 308         ao_raw_accel = 0;
 309 #endif
 310         ao_flight_tick = 0;
 311         for (;;) {
 312                 ao_wakeup(DATA_TO_XDATA(&ao_flight_adc));
 313                 ao_sleep(DATA_TO_XDATA(&ao_adc_head));
 314                 while (ao_flight_adc != ao_adc_head) {
 315                         __xdata struct ao_adc *ao_adc;
 316                         ao_flight_prev_tick = ao_flight_tick;
 317
 318                         /* Capture a sample */
 319                         ao_adc = &ao_adc_ring[ao_flight_adc];
 320                         ao_flight_tick = ao_adc->tick;
 321                         ao_raw_pres = ao_adc->pres;
 322                         ao_raw_alt = ao_pres_to_altitude(ao_raw_pres);
 323                         ao_raw_height = ao_raw_alt - ao_ground_height;
 324 #if HAS_ACCEL
 325                         ao_raw_accel = ao_adc->accel;
 326 #if HAS_ACCEL_REF
 327                         /*
 328                          * Ok, the math here is a bit tricky.
 329                          *
 330                          * ao_raw_accel:  ADC output for acceleration
 331                          * ao_accel_ref:  ADC output for the 5V reference.
 332                          * ao_cook_accel: Corrected acceleration value
 333                          * Vcc:           3.3V supply to the CC1111
 334                          * Vac:           5V supply to the accelerometer
 335                          * accel:         input voltage to accelerometer ADC pin
 336                          * ref:           input voltage to 5V reference ADC pin
 337                          *
 338                          *
 339                          * Measured acceleration is ratiometric to Vcc:
 340                          *
 341                          *     ao_raw_accel   accel
 342                          *     ------------ = -----
 343                          *        32767        Vcc
 344                          *
 345                          * Measured 5v reference is also ratiometric to Vcc:
 346                          *
 347                          *     ao_accel_ref    ref
 348                          *     ------------ = -----
 349                          *        32767        Vcc
 350                          *
 351                          *
 352                          *      ao_accel_ref = 32767 * (ref / Vcc)
 353                          *
 354                          * Acceleration is measured ratiometric to the 5V supply,
 355                          * so what we want is:
 356                          *
 357                          *      ao_cook_accel    accel
 358                          *      ------------- =  -----
 359                          *          32767         ref
 360                          *
 361                          *
 362                          *                      accel    Vcc
 363                          *                    = ----- *  ---
 364                          *                       Vcc     ref
 365                          *
 366                          *                      ao_raw_accel       32767
 367                          *                    = ------------ *  ------------
 368                          *                         32737        ao_accel_ref
 369                          *
 370                          * Multiply through by 32767:
 371                          *
 372                          *                      ao_raw_accel * 32767
 373                          *      ao_cook_accel = --------------------
 374                          *                          ao_accel_ref
 375                          *
 376                          * Now, the tricky part. Getting this to compile efficiently
 377                          * and keeping all of the values in-range.
 378                          *
 379                          * First off, we need to use a shift of 16 instead of * 32767 as SDCC
 380                          * does the obvious optimizations for byte-granularity shifts:
 381                          *
 382                          *      ao_cook_accel = (ao_raw_accel << 16) / ao_accel_ref
 383                          *
 384                          * Next, lets check our input ranges:
 385                          *
 386                          *      0 <= ao_raw_accel <= 0x7fff             (singled ended ADC conversion)
 387                          *      0x7000 <= ao_accel_ref <= 0x7fff        (the 5V ref value is close to 0x7fff)
 388                          *
 389                          * Plugging in our input ranges, we get an output range of 0 - 0x12490,
 390                          * which is 17 bits. That won't work. If we take the accel ref and shift
 391                          * by a bit, we'll change its range:
 392                          *
 393                          *      0xe000 <= ao_accel_ref<<1 <= 0xfffe
 394                          *
 395                          *      ao_cook_accel = (ao_raw_accel << 16) / (ao_accel_ref << 1)
 396                          *
 397                          * Now the output range is 0 - 0x9248, which nicely fits in 16 bits. It
 398                          * is, however, one bit too large for our signed computations. So, we
 399                          * take the result and shift that by a bit:
 400                          *
 401                          *      ao_cook_accel = ((ao_raw_accel << 16) / (ao_accel_ref << 1)) >> 1
 402                          *
 403                          * This finally creates an output range of 0 - 0x4924. As the ADC only
 404                          * provides 11 bits of data, we haven't actually lost any precision,
 405                          * just dropped a bit of noise off the low end.
 406                          */
 407                         ao_raw_accel = (uint16_t) ((((uint32_t) ao_raw_accel << 16) / (ao_accel_ref[ao_flight_adc] << 1))) >> 1;
 408                         ao_adc->accel = ao_raw_accel;
 409 #endif
 410 #endif
 411
 412                         if (ao_flight_state > ao_flight_idle) {
 413                                 ao_kalman_predict();
 414 #if HAS_ACCEL
 415                                 if (ao_flight_state <= ao_flight_coast) {
 416 #ifdef FORCE_ACCEL
 417                                         ao_kalman_correct_accel();
 418 #else
 419                                         ao_kalman_correct_both();
 420 #endif
 421                                 } else
 422 #endif
 423                                         ao_kalman_correct_baro();
 424                                 ao_height = from_fix(ao_k_height);
 425                                 ao_speed = from_fix(ao_k_speed);
 426                                 ao_accel = from_fix(ao_k_accel);
 427                                 if (ao_height > ao_max_height)
 428                                         ao_max_height = ao_height;
 429                         }
 430                         ao_flight_adc = ao_adc_ring_next(ao_flight_adc);
 431                 }
 432
 433                 switch (ao_flight_state) {
 434                 case ao_flight_startup:
 435
 436                         /* startup state:
 437                          *
 438                          * Collect 512 samples of acceleration and pressure
 439                          * data and average them to find the resting values
 440                          */
 441                         if (nsamples < 512) {
 442 #if HAS_ACCEL
 443                                 ao_raw_accel_sum += ao_raw_accel;
 444 #endif
 445                                 ao_raw_pres_sum += ao_raw_pres;
 446                                 ++nsamples;
 447                                 continue;
 448                         }
 449                         ao_config_get();
 450 #if HAS_ACCEL
 451                         ao_ground_accel = ao_raw_accel_sum >> 9;
 452                         ao_accel_2g = ao_config.accel_minus_g - ao_config.accel_plus_g;
 453                         ao_accel_scale = to_fix32(GRAVITY * 2 * 16) / ao_accel_2g;
 454 #endif
 455                         ao_ground_pres = ao_raw_pres_sum >> 9;
 456                         ao_ground_height = ao_pres_to_altitude(ao_ground_pres);
 457
 458                         /* Check to see what mode we should go to.
 459                          *  - Invalid mode if accel cal appears to be out
 460                          *  - pad mode if we're upright,
 461                          *  - idle mode otherwise
 462                          */
 463 #if HAS_ACCEL
 464                         if (ao_config.accel_plus_g == 0 ||
 465                             ao_config.accel_minus_g == 0 ||
 466                             ao_ground_accel < ao_config.accel_plus_g - ACCEL_NOSE_UP ||
 467                             ao_ground_accel > ao_config.accel_minus_g + ACCEL_NOSE_UP)
 468                         {
 469                                 /* Detected an accel value outside -1.5g to 1.5g
 470                                  * (or uncalibrated values), so we go into invalid mode
 471                                  */
 472                                 ao_flight_state = ao_flight_invalid;
 473
 474                         } else
 475 #endif
 476                                 if (!ao_flight_force_idle
 477 #if HAS_ACCEL
 478                                     && ao_ground_accel < ao_config.accel_plus_g + ACCEL_NOSE_UP
 479 #endif
 480                                         )
 481                         {
 482                                 /* Set pad mode - we can fly! */
 483                                 ao_flight_state = ao_flight_pad;
 484 #if HAS_USB
 485                                 /* Disable the USB controller in flight mode
 486                                  * to save power
 487                                  */
 488                                 ao_usb_disable();
 489 #endif
 490
 491                                 /* Disable packet mode in pad state */
 492                                 ao_packet_slave_stop();
 493
 494                                 /* Turn on telemetry system */
 495                                 ao_rdf_set(1);
 496                                 ao_telemetry_set_interval(AO_TELEMETRY_INTERVAL_PAD);
 497
 498                                 /* signal successful initialization by turning off the LED */
 499                                 ao_led_off(AO_LED_RED);
 500                         } else {
 501                                 /* Set idle mode */
 502                                 ao_flight_state = ao_flight_idle;
 503
 504                                 /* signal successful initialization by turning off the LED */
 505                                 ao_led_off(AO_LED_RED);
 506                         }
 507                         /* wakeup threads due to state change */
 508                         ao_wakeup(DATA_TO_XDATA(&ao_flight_state));
 509
 510                         break;
 511                 case ao_flight_pad:
 512
 513                         /* pad to boost:
 514                          *
 515                          * barometer: > 20m vertical motion
 516                          *             OR
 517                          * accelerometer: > 2g AND velocity > 5m/s
 518                          *
 519                          * The accelerometer should always detect motion before
 520                          * the barometer, but we use both to make sure this
 521                          * transition is detected. If the device
 522                          * doesn't have an accelerometer, then ignore the
 523                          * speed and acceleration as they are quite noisy
 524                          * on the pad.
 525                          */
 526                         if (ao_height > AO_M_TO_HEIGHT(20)
 527 #if HAS_ACCEL
 528                             || (ao_accel > AO_MSS_TO_ACCEL(20) &&
 529                                 ao_speed > AO_MS_TO_SPEED(5))
 530 #endif
 531                                 )
 532                         {
 533                                 ao_flight_state = ao_flight_boost;
 534                                 ao_launch_tick = ao_flight_tick;
 535
 536                                 /* start logging data */
 537                                 ao_log_start();
 538
 539                                 /* Increase telemetry rate */
 540                                 ao_telemetry_set_interval(AO_TELEMETRY_INTERVAL_FLIGHT);
 541
 542                                 /* disable RDF beacon */
 543                                 ao_rdf_set(0);
 544
 545 #if HAS_GPS
 546                                 /* Record current GPS position by waking up GPS log tasks */
 547                                 ao_wakeup(&ao_gps_data);
 548                                 ao_wakeup(&ao_gps_tracking_data);
 549 #endif
 550
 551                                 ao_wakeup(DATA_TO_XDATA(&ao_flight_state));
 552                                 break;
 553                         }
 554                         break;
 555                 case ao_flight_boost:
 556
 557                         /* boost to fast:
 558                          *
 559                          * accelerometer: start to fall at > 1/4 G
 560                          *              OR
 561                          * time: boost for more than 15 seconds
 562                          *
 563                          * Detects motor burn out by the switch from acceleration to
 564                          * deceleration, or by waiting until the maximum burn duration
 565                          * (15 seconds) has past.
 566                          */
 567                         if ((ao_accel < AO_MSS_TO_ACCEL(-2.5) && ao_height > AO_M_TO_HEIGHT(100)) ||
 568                             (int16_t) (ao_flight_tick - ao_launch_tick) > BOOST_TICKS_MAX)
 569                         {
 570                                 ao_flight_state = ao_flight_fast;
 571                                 ao_wakeup(DATA_TO_XDATA(&ao_flight_state));
 572                                 break;
 573                         }
 574                         break;
 575                 case ao_flight_fast:
 576                         /*
 577                          * This is essentially the same as coast,
 578                          * but the barometer is being ignored as
 579                          * it may be unreliable.
 580                          */
 581                         if (ao_speed < AO_MS_TO_SPEED(AO_MAX_BARO_SPEED)) {
 582                                 ao_flight_state = ao_flight_coast;
 583                                 ao_wakeup(DATA_TO_XDATA(&ao_flight_state));
 584                                 break;
 585                         }
 586                         break;
 587                 case ao_flight_coast:
 588
 589                         /* apogee detect: coast to drogue deploy:
 590                          *
 591                          * speed: < 0
 592                          *
 593                          * Also make sure the model altitude is tracking
 594                          * the measured altitude reasonably closely; otherwise
 595                          * we're probably transsonic.
 596                          */
 597                         if (ao_speed < 0 && (ao_raw_alt >= AO_MAX_BARO_HEIGHT || ao_error_h_sq_avg < 100))
 598                         {
 599                                 /* ignite the drogue charge */
 600                                 ao_ignite(ao_igniter_drogue);
 601
 602                                 /* slow down the telemetry system */
 603                                 ao_telemetry_set_interval(AO_TELEMETRY_INTERVAL_RECOVER);
 604
 605                                 /*
 606                                  * Start recording min/max height
 607                                  * to figure out when the rocket has landed
 608                                  */
 609
 610                                 /* initialize interval values */
 611                                 ao_interval_end = ao_flight_tick + AO_INTERVAL_TICKS;
 612
 613                                 ao_interval_min_height = ao_interval_max_height = ao_height;
 614
 615                                 /* and enter drogue state */
 616                                 ao_flight_state = ao_flight_drogue;
 617                                 ao_wakeup(DATA_TO_XDATA(&ao_flight_state));
 618                         }
 619
 620                         break;
 621                 case ao_flight_drogue:
 622
 623                         /* drogue to main deploy:
 624                          *
 625                          * barometer: reach main deploy altitude
 626                          *
 627                          * Would like to use the accelerometer for this test, but
 628                          * the orientation of the flight computer is unknown after
 629                          * drogue deploy, so we ignore it. Could also detect
 630                          * high descent rate using the pressure sensor to
 631                          * recognize drogue deploy failure and eject the main
 632                          * at that point. Perhaps also use the drogue sense lines
 633                          * to notice continutity?
 634                          */
 635                         if (ao_height <= ao_config.main_deploy)
 636                         {
 637                                 ao_ignite(ao_igniter_main);
 638                                 ao_flight_state = ao_flight_main;
 639                                 ao_wakeup(DATA_TO_XDATA(&ao_flight_state));
 640                         }
 641
 642                         /* fall through... */
 643                 case ao_flight_main:
 644
 645                         /* drogue/main to land:
 646                          *
 647                          * barometer: altitude stable and within 1000m of the launch altitude
 648                          */
 649
 650                         if (ao_height < ao_interval_min_height)
 651                                 ao_interval_min_height = ao_height;
 652                         if (ao_height > ao_interval_max_height)
 653                                 ao_interval_max_height = ao_height;
 654
 655                         if ((int16_t) (ao_flight_tick - ao_interval_end) >= 0) {
 656                                 if (ao_height < AO_M_TO_HEIGHT(1000) &&
 657                                     ao_interval_max_height - ao_interval_min_height < AO_M_TO_HEIGHT(5))
 658                                 {
 659                                         ao_flight_state = ao_flight_landed;
 660
 661                                         /* turn off the ADC capture */
 662                                         ao_timer_set_adc_interval(0);
 663                                         /* Enable RDF beacon */
 664                                         ao_rdf_set(1);
 665
 666                                         ao_wakeup(DATA_TO_XDATA(&ao_flight_state));
 667                                 }
 668                                 ao_interval_min_height = ao_interval_max_height = ao_height;
 669                                 ao_interval_end = ao_flight_tick + AO_INTERVAL_TICKS;
 670                         }
 671                         break;
 672                 case ao_flight_landed:
 673                         break;
 674                 }
 675         }
 676 }
 677
 678 static __xdata struct ao_task   flight_task;
 679
 680 void
 681 ao_flight_init(void)
 682 {
 683         ao_flight_state = ao_flight_startup;
 684         ao_add_task(&flight_task, ao_flight, "flight");
 685 }