--- /dev/null
+/*
+ * 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
+ */
+
+__pdata int16_t ao_ground_pres; /* startup pressure */
+__pdata int16_t ao_ground_height; /* MSL of ao_ground_pres */
+
+#if HAS_ACCEL
+__pdata int16_t ao_ground_accel; /* startup acceleration */
+__pdata int16_t ao_accel_2g; /* factory accel calibration */
+__pdata int32_t ao_accel_scale; /* sensor to m/s² conversion */
+#endif
+
+static __pdata uint8_t ao_preflight; /* in preflight mode */
+
+static __pdata uint16_t nsamples;
+__pdata int32_t ao_sample_pres_sum;
+#if HAS_ACCEL
+__pdata 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;
+ } else {
+ 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);
+ ao_preflight = FALSE;
+ }
+}
+
+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
+ * = ------------ * ------------
+ * 32767 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;
+ if (ao_config.pad_orientation != AO_PAD_ORIENTATION_ANTENNA_UP)
+ ao_sample_accel = 0x7fff - ao_sample_accel;
+ 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;
+}
projects / fw / altos / blobdiff