2 * http://ad7zj.net/kd7lmo/aprsbeacon_code.html
4 * @mainpage Pico Beacon
6 * @section overview_sec Overview
8 * The Pico Beacon is an APRS based tracking beacon that operates in the UHF 420-450MHz band. The device utilizes a
9 * Microchip PIC 18F2525 embedded controller, Motorola M12+ GPS engine, and Analog Devices AD9954 DDS. The device is capable
10 * of generating a 1200bps A-FSK and 9600 bps FSK AX.25 compliant APRS (Automatic Position Reporting System) message.
14 * @section history_sec Revision History
16 * @subsection v305 V3.05
17 * 23 Dec 2006, Change include; (1) change printf format width to conform to ANSI standard when new CCS 4.xx compiler released.
20 * @subsection v304 V3.04
21 * 10 Jan 2006, Change include; (1) added amplitude control to engineering mode,
22 * (2) corrected number of bytes reported in log,
23 * (3) add engineering command to set high rate position reports (5 seconds), and
24 * (4) corrected size of LOG_COORD block when searching for end of log.
26 * @subsection v303 V3.03
27 * 15 Sep 2005, Change include; (1) removed AD9954 setting SDIO as input pin,
28 * (2) additional comments and Doxygen tags,
29 * (3) integration and test code calculates DDS FTW,
30 * (4) swapped bus and reference analog input ports (hardware change),
31 * (5) added message that indicates we are reading flash log and reports length,
32 * (6) report bus voltage in 10mV steps, and
33 * (7) change log type enumerated values to XORed nibbles for error detection.
36 * @subsection v302 V3.02
37 * 6 Apr 2005, Change include; (1) corrected tracked satellite count in NMEA-0183 $GPGGA message,
38 * (2) Doxygen documentation clean up and additions, and
39 * (3) added integration and test code to baseline.
42 * @subsection v301 V3.01
43 * 13 Jan 2005, Renamed project and files to Pico Beacon.
46 * @subsection v300 V3.00
47 * 15 Nov 2004, Change include; (1) Micro Beacon extreme hardware changes including integral transmitter,
48 * (2) PIC18F2525 processor,
49 * (3) AD9954 DDS support functions,
50 * (4) added comments and formatting for doxygen,
51 * (5) process GPS data with native Motorola protocol,
52 * (6) generate plain text $GPGGA and $GPRMC messages,
53 * (7) power down GPS 5 hours after lock,
54 * (8) added flight data recorder, and
55 * (9) added diagnostics terminal mode.
58 * @subsection v201 V2.01
59 * 30 Jan 2004, Change include; (1) General clean up of in-line documentation, and
60 * (2) changed temperature resolution to 0.1 degrees F.
63 * @subsection v200 V2.00
64 * 26 Oct 2002, Change include; (1) Micro Beacon II hardware changes including PIC18F252 processor,
66 * (3) GPS power control,
67 * (4) additional ADC input, and
68 * (5) LM60 temperature sensor.
71 * @subsection v101 V1.01
72 * 5 Dec 2001, Change include; (1) Changed startup message, and
73 * (2) applied SEPARATE pragma to several methods for memory usage.
76 * @subsection v100 V1.00
77 * 25 Sep 2001, Initial release. Flew ANSR-3 and ANSR-4.
83 * @section copyright_sec Copyright
85 * Copyright (c) 2001-2009 Michael Gray, KD7LMO
90 * @section gpl_sec GNU General Public License
92 * This program is free software; you can redistribute it and/or modify
93 * it under the terms of the GNU General Public License as published by
94 * the Free Software Foundation; either version 2 of the License, or
95 * (at your option) any later version.
97 * This program is distributed in the hope that it will be useful,
98 * but WITHOUT ANY WARRANTY; without even the implied warranty of
99 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
100 * GNU General Public License for more details.
102 * You should have received a copy of the GNU General Public License
103 * along with this program; if not, write to the Free Software
104 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
110 * @section design Design Details
112 * Provides design details on a variety of the components that make up the Pico Beacon.
118 * @page power Power Consumption
120 * Measured DC power consumption.
122 * 3VDC prime power current
127 * 18mA Processor running, all I/O off
131 * 120mA GPS running w/antenna
133 * 250mA DDS running and GPS w/antenna
135 * 420mA DDS running, GPS w/antenna, and PA chain on with no RF
148 // Public methods, constants, and data structures for each class.
150 static void timeInit(void);
152 static void tncInit(void);
153 static void tnc1200TimerTick(void);
158 * @defgroup sys System Library Functions
160 * Generic system functions similiar to the run-time C library.
166 * Calculate the CRC-16 CCITT of buffer that is length bytes long.
167 * The crc parameter allow the calculation on the CRC on multiple buffers.
169 * @param buffer Pointer to data buffer.
170 * @param length number of bytes in data buffer
171 * @param crc starting value
173 * @return CRC-16 of buffer[0 .. length]
175 static uint16_t sysCRC16(const uint8_t *buffer, uint8_t length, uint16_t crc)
177 uint8_t i, bit, value;
179 for (i = 0; i < length; ++i)
183 for (bit = 0; bit < 8; ++bit)
185 crc ^= (value & 0x01);
186 crc = ( crc & 0x01 ) ? ( crc >> 1 ) ^ 0x8408 : ( crc >> 1 );
197 * @defgroup rtc Real Time Interrupt tick
199 * Manage the built-in real time interrupt. The interrupt clock PRI is 104uS (9600 bps).
204 /// 16-bit NCO where the upper 8-bits are used to index into the frequency generation table.
205 static uint16_t timeNCO;
207 /// Audio tone NCO update step (phase).
208 static uint16_t timeNCOFreq;
211 * Initialize the real-time clock.
213 static void timeInit()
216 timeNCOFreq = 0x2000;
222 * @defgroup tnc TNC (Terminal Node Controller)
224 * Functions that provide a subset of the TNC functions.
229 /// The number of start flag bytes to send before the packet message. (360bits * 1200bps = 300mS)
230 #define TNC_TX_DELAY 45
232 /// The size of the TNC output buffer.
233 #define TNC_BUFFER_SIZE 40
235 /// States that define the current mode of the 1200 bps (A-FSK) state machine.
238 /// Stand by state ready to accept new message.
241 /// 0x7E bit stream pattern used to define start of APRS message.
244 /// Transmit the AX.25 header that contains the source/destination call signs, APRS path, and flags.
247 /// Transmit the message data.
250 /// Transmit the end flag sequence.
252 } TNC_TX_1200BPS_STATE;
254 /// AX.25 compliant packet header that contains destination, station call sign, and path.
255 /// 0x76 for SSID-11, 0x78 for SSID-12
256 static uint8_t TNC_AX25_HEADER[] = {
257 'A' << 1, 'P' << 1, 'A' << 1, 'M' << 1, ' ' << 1, ' ' << 1, 0x60,
258 'N' << 1, '0' << 1, 'C' << 1, 'A' << 1, 'L' << 1, 'L' << 1, 0x78,
259 'W' << 1, 'I' << 1, 'D' << 1, 'E' << 1, '2' << 1, ' ' << 1, 0x65,
262 #define TNC_CALLSIGN_OFF 7
263 #define TNC_CALLSIGN_LEN 6
264 #define TNC_SSID_OFF 13
272 for (i = 0; i < TNC_CALLSIGN_LEN; i++) {
273 if (!ao_config.callsign[i])
275 TNC_AX25_HEADER[TNC_CALLSIGN_OFF + i] = ao_config.callsign[i] << 1;
277 for (; i < TNC_CALLSIGN_LEN; i++)
278 TNC_AX25_HEADER[TNC_CALLSIGN_OFF + i] = ' ' << 1;
279 TNC_AX25_HEADER[TNC_SSID_OFF] = 0x60 | ((ao_serial_number % 10) << 1);
283 /// The next bit to transmit.
284 static uint8_t tncTxBit;
286 /// Current mode of the 1200 bps state machine.
287 static TNC_TX_1200BPS_STATE tncMode;
289 /// Counter for each bit (0 - 7) that we are going to transmit.
290 static uint8_t tncBitCount;
292 /// A shift register that holds the data byte as we bit shift it for transmit.
293 static uint8_t tncShift;
295 /// Index into the APRS header and data array for each byte as we transmit it.
296 static uint8_t tncIndex;
298 /// The number of bytes in the message portion of the AX.25 message.
299 static uint8_t tncLength;
301 /// A copy of the last 5 bits we've transmitted to determine if we need to bit stuff on the next bit.
302 static uint8_t tncBitStuff;
304 /// Buffer to hold the message portion of the AX.25 packet as we prepare it.
305 static uint8_t tncBuffer[TNC_BUFFER_SIZE];
308 * Initialize the TNC internal variables.
310 static void tncInit()
313 tncMode = TNC_TX_READY;
317 * Method that is called every 833uS to transmit the 1200bps A-FSK data stream.
318 * The provides the pre and postamble as well as the bit stuffed data stream.
320 static void tnc1200TimerTick()
322 // Set the A-FSK frequency.
323 if (tncTxBit == 0x00)
324 timeNCOFreq = 0x2000;
326 timeNCOFreq = 0x3aab;
331 // Generate a test signal alteranting between high and low tones.
332 tncTxBit = (tncTxBit == 0 ? 1 : 0);
336 // The variable tncShift contains the lastest data byte.
337 // NRZI enocde the data stream.
338 if ((tncShift & 0x01) == 0x00) {
345 // When the flag is done, determine if we need to send more or data.
346 if (++tncBitCount == 8)
351 // Once we transmit x mS of flags, send the data.
352 // txDelay bytes * 8 bits/byte * 833uS/bit = x mS
353 if (++tncIndex == TNC_TX_DELAY)
356 tncShift = TNC_AX25_HEADER[0];
358 tncMode = TNC_TX_HEADER;
361 tncShift = tncShift >> 1;
365 // Determine if we have sent 5 ones in a row, if we have send a zero.
366 if (tncBitStuff == 0x1f)
377 // The variable tncShift contains the lastest data byte.
378 // NRZI enocde the data stream.
379 if ((tncShift & 0x01) == 0x00) {
386 // Save the data stream so we can determine if bit stuffing is
387 // required on the next bit time.
388 tncBitStuff = ((tncBitStuff << 1) | (tncShift & 0x01)) & 0x1f;
390 // If all the bits were shifted, get the next byte.
391 if (++tncBitCount == 8)
395 // After the header is sent, then send the data.
396 if (++tncIndex == sizeof(TNC_AX25_HEADER))
399 tncShift = tncBuffer[0];
400 tncMode = TNC_TX_DATA;
402 tncShift = TNC_AX25_HEADER[tncIndex];
405 tncShift = tncShift >> 1;
410 // Determine if we have sent 5 ones in a row, if we have send a zero.
411 if (tncBitStuff == 0x1f)
422 // The variable tncShift contains the lastest data byte.
423 // NRZI enocde the data stream.
424 if ((tncShift & 0x01) == 0x00) {
431 // Save the data stream so we can determine if bit stuffing is
432 // required on the next bit time.
433 tncBitStuff = ((tncBitStuff << 1) | (tncShift & 0x01)) & 0x1f;
435 // If all the bits were shifted, get the next byte.
436 if (++tncBitCount == 8)
440 // If everything was sent, transmit closing flags.
441 if (++tncIndex == tncLength)
445 tncMode = TNC_TX_END;
447 tncShift = tncBuffer[tncIndex];
450 tncShift = tncShift >> 1;
455 // The variable tncShift contains the lastest data byte.
456 // NRZI enocde the data stream.
457 if ((tncShift & 0x01) == 0x00) {
464 // If all the bits were shifted, get the next one.
465 if (++tncBitCount == 8)
470 // Transmit two closing flags.
473 tncMode = TNC_TX_READY;
478 tncShift = tncShift >> 1;
484 static void tncCompressInt(uint8_t *dest, int32_t value, int len) {
486 for (i = len - 1; i >= 0; i--) {
487 dest[i] = value % 91 + 33;
492 static int ao_num_sats(void)
497 for (i = 0; i < ao_gps_tracking_data.channels; i++) {
498 if (ao_gps_tracking_data.sats[i].svid)
504 static char ao_gps_locked(void)
506 if (ao_gps_data.flags & AO_GPS_VALID)
512 static int tncComment(uint8_t *buf)
515 struct ao_data packet;
517 ao_arch_critical(ao_data_get(&packet););
519 int16_t battery = ao_battery_decivolt(packet.adc.v_batt);
520 #ifdef AO_SENSE_DROGUE
521 int16_t apogee = ao_ignite_decivolt(AO_SENSE_DROGUE(&packet));
524 int16_t main = ao_ignite_decivolt(AO_SENSE_MAIN(&packet));
527 return sprintf((char *) buf,
529 #ifdef AO_SENSE_DROGUE
540 #ifdef AO_SENSE_DROGUE
551 return sprintf((char *) buf,
559 * APRS use a log encoding of altitude with a base of 1.002, such that
561 * feet = 1.002 ** encoded_altitude
563 * meters = (1.002 ** encoded_altitude) * 0.3048
565 * log2(meters) = log2(1.002 ** encoded_altitude) + log2(0.3048)
567 * log2(meters) = encoded_altitude * log2(1.002) + log2(0.3048)
569 * encoded_altitude = (log2(meters) - log2(0.3048)) / log2(1.002)
571 * encoded_altitude = (log2(meters) + log2(1/0.3048)) * (1/log2(1.002))
573 * We need 9 bits of mantissa to hold 1/log2(1.002) (~ 347), which leaves us
574 * 23 bits of fraction. That turns out to be *just* enough to avoid any
575 * errors in the result (cool, huh?).
578 #define fixed23_int(x) ((uint32_t) ((x) << 23))
579 #define fixed23_one fixed23_int(1)
580 #define fixed23_two fixed23_int(2)
581 #define fixed23_half (fixed23_one >> 1)
582 #define fixed23_floor(x) ((x) >> 23)
583 #define fixed23_real(x) ((uint32_t) ((x) * fixed23_one + 0.5))
585 static inline uint64_t
586 fixed23_mul(uint32_t x, uint32_t y)
588 return ((uint64_t) x * y + fixed23_half) >> 23;
592 * Use 30 fraction bits for the altitude. We need two bits at the
593 * top as we need to handle x, where 0 <= x < 4. We don't
594 * need 30 bits, but it's actually easier this way as we normalize
595 * the incoming value to 1 <= x < 2, and having the integer portion
596 * way up high means we don't have to deal with shifting in both
597 * directions to cover from 0 to 2**30-1.
600 #define fixed30_int(x) ((uint32_t) ((x) << 30))
601 #define fixed30_one fixed30_int(1)
602 #define fixed30_half (fixed30_one >> 1)
603 #define fixed30_two fixed30_int(2)
605 static inline uint32_t
606 fixed30_mul(uint32_t x, uint32_t y)
608 return ((uint64_t) x * y + fixed30_half) >> 30;
612 * Fixed point log2. Takes integer argument, returns
613 * fixed point result with 23 bits of fraction
617 ao_fixed_log2(uint32_t x)
620 uint32_t frac = fixed23_one;
622 /* Bounds check for sanity */
626 if (x >= fixed30_one)
630 * Normalize and compute integer log portion
632 * This makes 1 <= x < 2, and computes result to be
633 * the integer portion of the log2 of x
636 for (result = fixed23_int(30); x < fixed30_one; result -= fixed23_one, x <<= 1)
640 * Given x, find y and n such that:
642 * x = y * 2**n 1 <= y < 2
648 * Now, repeatedly square y to find find z and m such that:
650 * z = y ** (2**m) 2 <= z < 4
652 * This is possible because 1 <= y < 2
654 * lb(y) = lb(z) / 2**m
660 * = 2**-m + 2**-m * lb(z/2)
662 * Note that if 2 <= z < 4, then 1 <= (z/2) < 2, so we can
663 * iterate to find lb(z/2)
665 * In this implementation, we don't care about the 'm' value,
666 * instead we only care about 2**-m, which we store in 'frac'
669 while (frac != 0 && x != fixed30_one) {
670 /* Repeatedly square x until 2 <= x < 4 */
671 while (x < fixed30_two) {
672 x = fixed30_mul(x, x);
674 /* Divide the fractional result bit by 2 */
678 /* Add in this result bit */
681 /* Make 1 <= x < 2 again and iterate */
687 #define APRS_LOG_CONVERT fixed23_real(1.714065192056127)
688 #define APRS_LOG_BASE fixed23_real(346.920048461100941)
691 ao_aprs_encode_altitude(int meters)
693 return fixed23_floor(fixed23_mul(ao_fixed_log2(meters) + APRS_LOG_CONVERT, APRS_LOG_BASE) + fixed23_half);
697 * Generate the plain text position packet.
699 static int tncPositionPacket(void)
701 static int32_t latitude;
702 static int32_t longitude;
703 static int32_t altitude;
704 int32_t lat, lon, alt;
707 if (ao_gps_data.flags & AO_GPS_VALID) {
708 latitude = ao_gps_data.latitude;
709 longitude = ao_gps_data.longitude;
710 altitude = ao_gps_data.altitude;
718 /* Symbol table ID */
721 lat = ((uint64_t) 380926 * (900000000 - latitude)) / 10000000;
722 lon = ((uint64_t) 190463 * (1800000000 + longitude)) / 10000000;
724 alt = ao_aprs_encode_altitude(altitude);
726 tncCompressInt(buf, lat, 4);
728 tncCompressInt(buf, lon, 4);
734 tncCompressInt(buf, alt, 2);
737 *buf++ = 33 + ((1 << 5) | (2 << 3));
739 buf += tncComment(buf);
741 return buf - tncBuffer;
745 tncFill(uint8_t *buf, int16_t len)
751 while (tncMode != TNC_TX_READY && l < len) {
753 for (bit = 0; bit < 8; bit++) {
754 b = b << 1 | (timeNCO >> 15);
755 timeNCO += timeNCOFreq;
761 if (tncMode == TNC_TX_READY)
767 * Prepare an AX.25 data packet. Each time this method is called, it automatically
768 * rotates through 1 of 3 messages.
770 * @param dataMode enumerated type that specifies 1200bps A-FSK or 9600bps FSK
772 void ao_aprs_send(void)
780 tncLength = tncPositionPacket();
782 // Calculate the CRC for the header and message.
783 crc = sysCRC16(TNC_AX25_HEADER, sizeof(TNC_AX25_HEADER), 0xffff);
784 crc = sysCRC16(tncBuffer, tncLength, crc ^ 0xffff);
786 // Save the CRC in the message.
787 tncBuffer[tncLength++] = crc & 0xff;
788 tncBuffer[tncLength++] = (crc >> 8) & 0xff;
790 // Prepare the variables that are used in the real-time clock interrupt.
795 tncMode = TNC_TX_SYNC;
797 ao_radio_send_aprs(tncFill);