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Diffstat (limited to 'src/ao_sample.c')
| -rw-r--r-- | src/ao_sample.c | 206 |
1 files changed, 206 insertions, 0 deletions
diff --git a/src/ao_sample.c b/src/ao_sample.c new file mode 100644 index 00000000..ef403393 --- /dev/null +++ b/src/ao_sample.c @@ -0,0 +1,206 @@ +/* + * Copyright © 2011 Keith Packard <keithp@keithp.com> + * + * This program is free software; you can redistribute it and/or modify + * it under the terms of the GNU General Public License as published by + * the Free Software Foundation; version 2 of the License. + * + * This program is distributed in the hope that it will be useful, but + * WITHOUT ANY WARRANTY; without even the implied warranty of + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + * General Public License for more details. + * + * You should have received a copy of the GNU General Public License along + * with this program; if not, write to the Free Software Foundation, Inc., + * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA. + */ + +#ifndef AO_FLIGHT_TEST +#include "ao.h" +#endif + +/* + * Current sensor values + */ + +__pdata uint16_t ao_sample_tick; /* time of last data */ +__pdata int16_t ao_sample_pres; +__pdata int16_t ao_sample_alt; +__pdata int16_t ao_sample_height; +#if HAS_ACCEL +__pdata int16_t ao_sample_accel; +#endif + +__data uint8_t ao_sample_adc; + +/* + * Sensor calibration values + */ + +__xdata int16_t ao_ground_pres; /* startup pressure */ +__xdata int16_t ao_ground_height; /* MSL of ao_ground_pres */ + +#if HAS_ACCEL +__xdata int16_t ao_ground_accel; /* startup acceleration */ +__xdata int16_t ao_accel_2g; /* factory accel calibration */ +__xdata int32_t ao_accel_scale; /* sensor to m/s² conversion */ +#endif + +static __xdata uint8_t ao_preflight; /* in preflight mode */ + +static __xdata uint16_t nsamples; +__xdata int32_t ao_sample_pres_sum; +#if HAS_ACCEL +__xdata int32_t ao_sample_accel_sum; +#endif + +static void +ao_sample_preflight(void) +{ + /* startup state: + * + * Collect 512 samples of acceleration and pressure + * data and average them to find the resting values + */ + if (nsamples < 512) { +#if HAS_ACCEL + ao_sample_accel_sum += ao_sample_accel; +#endif + ao_sample_pres_sum += ao_sample_pres; + ++nsamples; + ao_preflight = FALSE; + } + ao_config_get(); +#if HAS_ACCEL + ao_ground_accel = ao_sample_accel_sum >> 9; + ao_accel_2g = ao_config.accel_minus_g - ao_config.accel_plus_g; + ao_accel_scale = to_fix32(GRAVITY * 2 * 16) / ao_accel_2g; +#endif + ao_ground_pres = ao_sample_pres_sum >> 9; + ao_ground_height = ao_pres_to_altitude(ao_ground_pres); +} + +uint8_t +ao_sample(void) +{ + ao_wakeup(DATA_TO_XDATA(&ao_sample_adc)); + ao_sleep(DATA_TO_XDATA(&ao_adc_head)); + while (ao_sample_adc != ao_adc_head) { + __xdata struct ao_adc *ao_adc; + + /* Capture a sample */ + ao_adc = &ao_adc_ring[ao_sample_adc]; + ao_sample_tick = ao_adc->tick; + ao_sample_pres = ao_adc->pres; + ao_sample_alt = ao_pres_to_altitude(ao_sample_pres); + ao_sample_height = ao_sample_alt - ao_ground_height; +#if HAS_ACCEL + ao_sample_accel = ao_adc->accel; +#if HAS_ACCEL_REF + /* + * Ok, the math here is a bit tricky. + * + * ao_sample_accel: ADC output for acceleration + * ao_accel_ref: ADC output for the 5V reference. + * ao_cook_accel: Corrected acceleration value + * Vcc: 3.3V supply to the CC1111 + * Vac: 5V supply to the accelerometer + * accel: input voltage to accelerometer ADC pin + * ref: input voltage to 5V reference ADC pin + * + * + * Measured acceleration is ratiometric to Vcc: + * + * ao_sample_accel accel + * ------------ = ----- + * 32767 Vcc + * + * Measured 5v reference is also ratiometric to Vcc: + * + * ao_accel_ref ref + * ------------ = ----- + * 32767 Vcc + * + * + * ao_accel_ref = 32767 * (ref / Vcc) + * + * Acceleration is measured ratiometric to the 5V supply, + * so what we want is: + * + * ao_cook_accel accel + * ------------- = ----- + * 32767 ref + * + * + * accel Vcc + * = ----- * --- + * Vcc ref + * + * ao_sample_accel 32767 + * = ------------ * ------------ + * 32737 ao_accel_ref + * + * Multiply through by 32767: + * + * ao_sample_accel * 32767 + * ao_cook_accel = -------------------- + * ao_accel_ref + * + * Now, the tricky part. Getting this to compile efficiently + * and keeping all of the values in-range. + * + * First off, we need to use a shift of 16 instead of * 32767 as SDCC + * does the obvious optimizations for byte-granularity shifts: + * + * ao_cook_accel = (ao_sample_accel << 16) / ao_accel_ref + * + * Next, lets check our input ranges: + * + * 0 <= ao_sample_accel <= 0x7fff (singled ended ADC conversion) + * 0x7000 <= ao_accel_ref <= 0x7fff (the 5V ref value is close to 0x7fff) + * + * Plugging in our input ranges, we get an output range of 0 - 0x12490, + * which is 17 bits. That won't work. If we take the accel ref and shift + * by a bit, we'll change its range: + * + * 0xe000 <= ao_accel_ref<<1 <= 0xfffe + * + * ao_cook_accel = (ao_sample_accel << 16) / (ao_accel_ref << 1) + * + * Now the output range is 0 - 0x9248, which nicely fits in 16 bits. It + * is, however, one bit too large for our signed computations. So, we + * take the result and shift that by a bit: + * + * ao_cook_accel = ((ao_sample_accel << 16) / (ao_accel_ref << 1)) >> 1 + * + * This finally creates an output range of 0 - 0x4924. As the ADC only + * provides 11 bits of data, we haven't actually lost any precision, + * just dropped a bit of noise off the low end. + */ + ao_sample_accel = (uint16_t) ((((uint32_t) ao_sample_accel << 16) / (ao_accel_ref[ao_sample_adc] << 1))) >> 1; + ao_adc->accel = ao_sample_accel; +#endif +#endif + + if (ao_preflight) + ao_sample_preflight(); + else + ao_kalman(); + ao_sample_adc = ao_adc_ring_next(ao_sample_adc); + } + return !ao_preflight; +} + +void +ao_sample_init(void) +{ + nsamples = 0; + ao_sample_pres_sum = 0; + ao_sample_pres = 0; +#if HAS_ACCEL + ao_sample_accel_sum = 0; + ao_sample_accel = 0; +#endif + ao_sample_adc = ao_adc_head; + ao_preflight = TRUE; +} |