1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
|
/*
* 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;
}
|
