source: flair-src/branches/mavlink/tools/Controller/Mavlink/src/include/mavlink_helpers.h@ 79

Last change on this file since 79 was 75, checked in by Thomas Fuhrmann, 8 years ago

Change the version of mavlink generated messages and rename it to include
File size: 21.2 KB
Line 
1#ifndef _MAVLINK_HELPERS_H_
2#define _MAVLINK_HELPERS_H_
3
4#include "string.h"
5#include "checksum.h"
6#include "mavlink_types.h"
7#include "mavlink_conversions.h"
8
9#ifndef MAVLINK_HELPER
10#define MAVLINK_HELPER
11#endif
12
13/*
14 * Internal function to give access to the channel status for each channel
15 */
16#ifndef MAVLINK_GET_CHANNEL_STATUS
17MAVLINK_HELPER mavlink_status_t* mavlink_get_channel_status(uint8_t chan)
18{
19#ifdef MAVLINK_EXTERNAL_RX_STATUS
20 // No m_mavlink_status array defined in function,
21 // has to be defined externally
22#else
23 static mavlink_status_t m_mavlink_status[MAVLINK_COMM_NUM_BUFFERS];
24#endif
25 return &m_mavlink_status[chan];
26}
27#endif
28
29/*
30 * Internal function to give access to the channel buffer for each channel
31 */
32#ifndef MAVLINK_GET_CHANNEL_BUFFER
33MAVLINK_HELPER mavlink_message_t* mavlink_get_channel_buffer(uint8_t chan)
34{
35
36#ifdef MAVLINK_EXTERNAL_RX_BUFFER
37 // No m_mavlink_buffer array defined in function,
38 // has to be defined externally
39#else
40 static mavlink_message_t m_mavlink_buffer[MAVLINK_COMM_NUM_BUFFERS];
41#endif
42 return &m_mavlink_buffer[chan];
43}
44#endif
45
46/**
47 * @brief Reset the status of a channel.
48 */
49MAVLINK_HELPER void mavlink_reset_channel_status(uint8_t chan)
50{
51 mavlink_status_t *status = mavlink_get_channel_status(chan);
52 status->parse_state = MAVLINK_PARSE_STATE_IDLE;
53}
54
55/**
56 * @brief Finalize a MAVLink message with channel assignment
57 *
58 * This function calculates the checksum and sets length and aircraft id correctly.
59 * It assumes that the message id and the payload are already correctly set. This function
60 * can also be used if the message header has already been written before (as in mavlink_msg_xxx_pack
61 * instead of mavlink_msg_xxx_pack_headerless), it just introduces little extra overhead.
62 *
63 * @param msg Message to finalize
64 * @param system_id Id of the sending (this) system, 1-127
65 * @param length Message length
66 */
67#if MAVLINK_CRC_EXTRA
68MAVLINK_HELPER uint16_t mavlink_finalize_message_chan(mavlink_message_t* msg, uint8_t system_id, uint8_t component_id,
69 uint8_t chan, uint8_t min_length, uint8_t length, uint8_t crc_extra)
70#else
71MAVLINK_HELPER uint16_t mavlink_finalize_message_chan(mavlink_message_t* msg, uint8_t system_id, uint8_t component_id,
72 uint8_t chan, uint8_t length)
73#endif
74{
75 // This code part is the same for all messages;
76 msg->magic = MAVLINK_STX;
77 msg->len = length;
78 msg->sysid = system_id;
79 msg->compid = component_id;
80 // One sequence number per channel
81 msg->seq = mavlink_get_channel_status(chan)->current_tx_seq;
82 mavlink_get_channel_status(chan)->current_tx_seq = mavlink_get_channel_status(chan)->current_tx_seq+1;
83 msg->checksum = crc_calculate(((const uint8_t*)(msg)) + 3, MAVLINK_CORE_HEADER_LEN);
84 crc_accumulate_buffer(&msg->checksum, _MAV_PAYLOAD(msg), msg->len);
85#if MAVLINK_CRC_EXTRA
86 crc_accumulate(crc_extra, &msg->checksum);
87#endif
88 mavlink_ck_a(msg) = (uint8_t)(msg->checksum & 0xFF);
89 mavlink_ck_b(msg) = (uint8_t)(msg->checksum >> 8);
90
91 return length + MAVLINK_NUM_NON_PAYLOAD_BYTES;
92}
93
94
95/**
96 * @brief Finalize a MAVLink message with MAVLINK_COMM_0 as default channel
97 */
98#if MAVLINK_CRC_EXTRA
99MAVLINK_HELPER uint16_t mavlink_finalize_message(mavlink_message_t* msg, uint8_t system_id, uint8_t component_id,
100 uint8_t min_length, uint8_t length, uint8_t crc_extra)
101{
102 return mavlink_finalize_message_chan(msg, system_id, component_id, MAVLINK_COMM_0, min_length, length, crc_extra);
103}
104#else
105MAVLINK_HELPER uint16_t mavlink_finalize_message(mavlink_message_t* msg, uint8_t system_id, uint8_t component_id,
106 uint8_t length)
107{
108 return mavlink_finalize_message_chan(msg, system_id, component_id, MAVLINK_COMM_0, length);
109}
110#endif
111
112#ifdef MAVLINK_USE_CONVENIENCE_FUNCTIONS
113MAVLINK_HELPER void _mavlink_send_uart(mavlink_channel_t chan, const char *buf, uint16_t len);
114
115/**
116 * @brief Finalize a MAVLink message with channel assignment and send
117 */
118#if MAVLINK_CRC_EXTRA
119MAVLINK_HELPER void _mav_finalize_message_chan_send(mavlink_channel_t chan, uint8_t msgid, const char *packet,
120 uint8_t min_length, uint8_t length, uint8_t crc_extra)
121#else
122MAVLINK_HELPER void _mav_finalize_message_chan_send(mavlink_channel_t chan, uint8_t msgid, const char *packet, uint8_t length)
123#endif
124{
125 uint16_t checksum;
126 uint8_t buf[MAVLINK_NUM_HEADER_BYTES];
127 uint8_t ck[2];
128 mavlink_status_t *status = mavlink_get_channel_status(chan);
129 buf[0] = MAVLINK_STX;
130 buf[1] = length;
131 buf[2] = status->current_tx_seq;
132 buf[3] = mavlink_system.sysid;
133 buf[4] = mavlink_system.compid;
134 buf[5] = msgid;
135 status->current_tx_seq++;
136 checksum = crc_calculate((const uint8_t*)&buf[1], MAVLINK_CORE_HEADER_LEN);
137 crc_accumulate_buffer(&checksum, packet, length);
138#if MAVLINK_CRC_EXTRA
139 crc_accumulate(crc_extra, &checksum);
140#endif
141 ck[0] = (uint8_t)(checksum & 0xFF);
142 ck[1] = (uint8_t)(checksum >> 8);
143
144 MAVLINK_START_UART_SEND(chan, MAVLINK_NUM_NON_PAYLOAD_BYTES + (uint16_t)length);
145 _mavlink_send_uart(chan, (const char *)buf, MAVLINK_NUM_HEADER_BYTES);
146 _mavlink_send_uart(chan, packet, length);
147 _mavlink_send_uart(chan, (const char *)ck, 2);
148 MAVLINK_END_UART_SEND(chan, MAVLINK_NUM_NON_PAYLOAD_BYTES + (uint16_t)length);
149}
150
151/**
152 * @brief re-send a message over a uart channel
153 * this is more stack efficient than re-marshalling the message
154 */
155MAVLINK_HELPER void _mavlink_resend_uart(mavlink_channel_t chan, const mavlink_message_t *msg)
156{
157 uint8_t ck[2];
158
159 ck[0] = (uint8_t)(msg->checksum & 0xFF);
160 ck[1] = (uint8_t)(msg->checksum >> 8);
161 // XXX use the right sequence here
162
163 MAVLINK_START_UART_SEND(chan, MAVLINK_NUM_NON_PAYLOAD_BYTES + msg->len);
164 _mavlink_send_uart(chan, (const char *)&msg->magic, MAVLINK_NUM_HEADER_BYTES);
165 _mavlink_send_uart(chan, _MAV_PAYLOAD(msg), msg->len);
166 _mavlink_send_uart(chan, (const char *)ck, 2);
167 MAVLINK_END_UART_SEND(chan, MAVLINK_NUM_NON_PAYLOAD_BYTES + msg->len);
168}
169#endif // MAVLINK_USE_CONVENIENCE_FUNCTIONS
170
171/**
172 * @brief Pack a message to send it over a serial byte stream
173 */
174MAVLINK_HELPER uint16_t mavlink_msg_to_send_buffer(uint8_t *buffer, const mavlink_message_t *msg)
175{
176 memcpy(buffer, (const uint8_t *)&msg->magic, MAVLINK_NUM_HEADER_BYTES + (uint16_t)msg->len);
177
178 uint8_t *ck = buffer + (MAVLINK_NUM_HEADER_BYTES + (uint16_t)msg->len);
179
180 ck[0] = (uint8_t)(msg->checksum & 0xFF);
181 ck[1] = (uint8_t)(msg->checksum >> 8);
182
183 return MAVLINK_NUM_NON_PAYLOAD_BYTES + (uint16_t)msg->len;
184}
185
186union __mavlink_bitfield {
187 uint8_t uint8;
188 int8_t int8;
189 uint16_t uint16;
190 int16_t int16;
191 uint32_t uint32;
192 int32_t int32;
193};
194
195
196MAVLINK_HELPER void mavlink_start_checksum(mavlink_message_t* msg)
197{
198 crc_init(&msg->checksum);
199}
200
201MAVLINK_HELPER void mavlink_update_checksum(mavlink_message_t* msg, uint8_t c)
202{
203 crc_accumulate(c, &msg->checksum);
204}
205
206/**
207 * This is a varient of mavlink_frame_char() but with caller supplied
208 * parsing buffers. It is useful when you want to create a MAVLink
209 * parser in a library that doesn't use any global variables
210 *
211 * @param rxmsg parsing message buffer
212 * @param status parsing starus buffer
213 * @param c The char to parse
214 *
215 * @param returnMsg NULL if no message could be decoded, the message data else
216 * @param returnStats if a message was decoded, this is filled with the channel's stats
217 * @return 0 if no message could be decoded, 1 on good message and CRC, 2 on bad CRC
218 *
219 * A typical use scenario of this function call is:
220 *
221 * @code
222 * #include <mavlink.h>
223 *
224 * mavlink_message_t msg;
225 * int chan = 0;
226 *
227 *
228 * while(serial.bytesAvailable > 0)
229 * {
230 * uint8_t byte = serial.getNextByte();
231 * if (mavlink_frame_char(chan, byte, &msg) != MAVLINK_FRAMING_INCOMPLETE)
232 * {
233 * printf("Received message with ID %d, sequence: %d from component %d of system %d", msg.msgid, msg.seq, msg.compid, msg.sysid);
234 * }
235 * }
236 *
237 *
238 * @endcode
239 */
240MAVLINK_HELPER uint8_t mavlink_frame_char_buffer(mavlink_message_t* rxmsg,
241 mavlink_status_t* status,
242 uint8_t c,
243 mavlink_message_t* r_message,
244 mavlink_status_t* r_mavlink_status)
245{
246 /*
247 default message crc function. You can override this per-system to
248 put this data in a different memory segment
249 */
250#if MAVLINK_CRC_EXTRA
251#ifndef MAVLINK_MESSAGE_CRC
252 static const uint8_t mavlink_message_crcs[256] = MAVLINK_MESSAGE_CRCS;
253#define MAVLINK_MESSAGE_CRC(msgid) mavlink_message_crcs[msgid]
254#endif
255#endif
256
257 /* Enable this option to check the length of each message.
258 This allows invalid messages to be caught much sooner. Use if the transmission
259 medium is prone to missing (or extra) characters (e.g. a radio that fades in
260 and out). Only use if the channel will only contain messages types listed in
261 the headers.
262 */
263#ifdef MAVLINK_CHECK_MESSAGE_LENGTH
264#ifndef MAVLINK_MESSAGE_LENGTH
265 static const uint8_t mavlink_message_lengths[256] = MAVLINK_MESSAGE_LENGTHS;
266#define MAVLINK_MESSAGE_LENGTH(msgid) mavlink_message_lengths[msgid]
267#endif
268#endif
269
270 int bufferIndex = 0;
271
272 status->msg_received = MAVLINK_FRAMING_INCOMPLETE;
273
274 switch (status->parse_state)
275 {
276 case MAVLINK_PARSE_STATE_UNINIT:
277 case MAVLINK_PARSE_STATE_IDLE:
278 if (c == MAVLINK_STX)
279 {
280 status->parse_state = MAVLINK_PARSE_STATE_GOT_STX;
281 rxmsg->len = 0;
282 rxmsg->magic = c;
283 mavlink_start_checksum(rxmsg);
284 }
285 break;
286
287 case MAVLINK_PARSE_STATE_GOT_STX:
288 if (status->msg_received
289/* Support shorter buffers than the
290 default maximum packet size */
291#if (MAVLINK_MAX_PAYLOAD_LEN < 255)
292 || c > MAVLINK_MAX_PAYLOAD_LEN
293#endif
294 )
295 {
296 status->buffer_overrun++;
297 status->parse_error++;
298 status->msg_received = 0;
299 status->parse_state = MAVLINK_PARSE_STATE_IDLE;
300 }
301 else
302 {
303 // NOT counting STX, LENGTH, SEQ, SYSID, COMPID, MSGID, CRC1 and CRC2
304 rxmsg->len = c;
305 status->packet_idx = 0;
306 mavlink_update_checksum(rxmsg, c);
307 status->parse_state = MAVLINK_PARSE_STATE_GOT_LENGTH;
308 }
309 break;
310
311 case MAVLINK_PARSE_STATE_GOT_LENGTH:
312 rxmsg->seq = c;
313 mavlink_update_checksum(rxmsg, c);
314 status->parse_state = MAVLINK_PARSE_STATE_GOT_SEQ;
315 break;
316
317 case MAVLINK_PARSE_STATE_GOT_SEQ:
318 rxmsg->sysid = c;
319 mavlink_update_checksum(rxmsg, c);
320 status->parse_state = MAVLINK_PARSE_STATE_GOT_SYSID;
321 break;
322
323 case MAVLINK_PARSE_STATE_GOT_SYSID:
324 rxmsg->compid = c;
325 mavlink_update_checksum(rxmsg, c);
326 status->parse_state = MAVLINK_PARSE_STATE_GOT_COMPID;
327 break;
328
329 case MAVLINK_PARSE_STATE_GOT_COMPID:
330#ifdef MAVLINK_CHECK_MESSAGE_LENGTH
331 if (rxmsg->len != MAVLINK_MESSAGE_LENGTH(c))
332 {
333 status->parse_error++;
334 status->parse_state = MAVLINK_PARSE_STATE_IDLE;
335 break;
336 }
337#endif
338 rxmsg->msgid = c;
339 mavlink_update_checksum(rxmsg, c);
340 if (rxmsg->len == 0)
341 {
342 status->parse_state = MAVLINK_PARSE_STATE_GOT_PAYLOAD;
343 }
344 else
345 {
346 status->parse_state = MAVLINK_PARSE_STATE_GOT_MSGID;
347 }
348 break;
349
350 case MAVLINK_PARSE_STATE_GOT_MSGID:
351 _MAV_PAYLOAD_NON_CONST(rxmsg)[status->packet_idx++] = (char)c;
352 mavlink_update_checksum(rxmsg, c);
353 if (status->packet_idx == rxmsg->len)
354 {
355 status->parse_state = MAVLINK_PARSE_STATE_GOT_PAYLOAD;
356 }
357 break;
358
359 case MAVLINK_PARSE_STATE_GOT_PAYLOAD:
360#if MAVLINK_CRC_EXTRA
361 mavlink_update_checksum(rxmsg, MAVLINK_MESSAGE_CRC(rxmsg->msgid));
362#endif
363 if (c != (rxmsg->checksum & 0xFF)) {
364 status->parse_state = MAVLINK_PARSE_STATE_GOT_BAD_CRC1;
365 } else {
366 status->parse_state = MAVLINK_PARSE_STATE_GOT_CRC1;
367 }
368 _MAV_PAYLOAD_NON_CONST(rxmsg)[status->packet_idx] = (char)c;
369 break;
370
371 case MAVLINK_PARSE_STATE_GOT_CRC1:
372 case MAVLINK_PARSE_STATE_GOT_BAD_CRC1:
373 if (status->parse_state == MAVLINK_PARSE_STATE_GOT_BAD_CRC1 || c != (rxmsg->checksum >> 8)) {
374 // got a bad CRC message
375 status->msg_received = MAVLINK_FRAMING_BAD_CRC;
376 } else {
377 // Successfully got message
378 status->msg_received = MAVLINK_FRAMING_OK;
379 }
380 status->parse_state = MAVLINK_PARSE_STATE_IDLE;
381 _MAV_PAYLOAD_NON_CONST(rxmsg)[status->packet_idx+1] = (char)c;
382 memcpy(r_message, rxmsg, sizeof(mavlink_message_t));
383 break;
384 }
385
386 bufferIndex++;
387 // If a message has been sucessfully decoded, check index
388 if (status->msg_received == MAVLINK_FRAMING_OK)
389 {
390 //while(status->current_seq != rxmsg->seq)
391 //{
392 // status->packet_rx_drop_count++;
393 // status->current_seq++;
394 //}
395 status->current_rx_seq = rxmsg->seq;
396 // Initial condition: If no packet has been received so far, drop count is undefined
397 if (status->packet_rx_success_count == 0) status->packet_rx_drop_count = 0;
398 // Count this packet as received
399 status->packet_rx_success_count++;
400 }
401
402 r_message->len = rxmsg->len; // Provide visibility on how far we are into current msg
403 r_mavlink_status->parse_state = status->parse_state;
404 r_mavlink_status->packet_idx = status->packet_idx;
405 r_mavlink_status->current_rx_seq = status->current_rx_seq+1;
406 r_mavlink_status->packet_rx_success_count = status->packet_rx_success_count;
407 r_mavlink_status->packet_rx_drop_count = status->parse_error;
408 status->parse_error = 0;
409
410 if (status->msg_received == MAVLINK_FRAMING_BAD_CRC) {
411 /*
412 the CRC came out wrong. We now need to overwrite the
413 msg CRC with the one on the wire so that if the
414 caller decides to forward the message anyway that
415 mavlink_msg_to_send_buffer() won't overwrite the
416 checksum
417 */
418 r_message->checksum = _MAV_PAYLOAD(rxmsg)[status->packet_idx] | (_MAV_PAYLOAD(rxmsg)[status->packet_idx+1]<<8);
419 }
420
421 return status->msg_received;
422}
423
424/**
425 * This is a convenience function which handles the complete MAVLink parsing.
426 * the function will parse one byte at a time and return the complete packet once
427 * it could be successfully decoded. This function will return 0, 1 or
428 * 2 (MAVLINK_FRAMING_INCOMPLETE, MAVLINK_FRAMING_OK or MAVLINK_FRAMING_BAD_CRC)
429 *
430 * Messages are parsed into an internal buffer (one for each channel). When a complete
431 * message is received it is copies into *returnMsg and the channel's status is
432 * copied into *returnStats.
433 *
434 * @param chan ID of the current channel. This allows to parse different channels with this function.
435 * a channel is not a physical message channel like a serial port, but a logic partition of
436 * the communication streams in this case. COMM_NB is the limit for the number of channels
437 * on MCU (e.g. ARM7), while COMM_NB_HIGH is the limit for the number of channels in Linux/Windows
438 * @param c The char to parse
439 *
440 * @param returnMsg NULL if no message could be decoded, the message data else
441 * @param returnStats if a message was decoded, this is filled with the channel's stats
442 * @return 0 if no message could be decoded, 1 on good message and CRC, 2 on bad CRC
443 *
444 * A typical use scenario of this function call is:
445 *
446 * @code
447 * #include <mavlink.h>
448 *
449 * mavlink_message_t msg;
450 * int chan = 0;
451 *
452 *
453 * while(serial.bytesAvailable > 0)
454 * {
455 * uint8_t byte = serial.getNextByte();
456 * if (mavlink_frame_char(chan, byte, &msg) != MAVLINK_FRAMING_INCOMPLETE)
457 * {
458 * printf("Received message with ID %d, sequence: %d from component %d of system %d", msg.msgid, msg.seq, msg.compid, msg.sysid);
459 * }
460 * }
461 *
462 *
463 * @endcode
464 */
465MAVLINK_HELPER uint8_t mavlink_frame_char(uint8_t chan, uint8_t c, mavlink_message_t* r_message, mavlink_status_t* r_mavlink_status)
466{
467 return mavlink_frame_char_buffer(mavlink_get_channel_buffer(chan),
468 mavlink_get_channel_status(chan),
469 c,
470 r_message,
471 r_mavlink_status);
472}
473
474
475/**
476 * This is a convenience function which handles the complete MAVLink parsing.
477 * the function will parse one byte at a time and return the complete packet once
478 * it could be successfully decoded. This function will return 0 or 1.
479 *
480 * Messages are parsed into an internal buffer (one for each channel). When a complete
481 * message is received it is copies into *returnMsg and the channel's status is
482 * copied into *returnStats.
483 *
484 * @param chan ID of the current channel. This allows to parse different channels with this function.
485 * a channel is not a physical message channel like a serial port, but a logic partition of
486 * the communication streams in this case. COMM_NB is the limit for the number of channels
487 * on MCU (e.g. ARM7), while COMM_NB_HIGH is the limit for the number of channels in Linux/Windows
488 * @param c The char to parse
489 *
490 * @param returnMsg NULL if no message could be decoded, the message data else
491 * @param returnStats if a message was decoded, this is filled with the channel's stats
492 * @return 0 if no message could be decoded or bad CRC, 1 on good message and CRC
493 *
494 * A typical use scenario of this function call is:
495 *
496 * @code
497 * #include <mavlink.h>
498 *
499 * mavlink_message_t msg;
500 * int chan = 0;
501 *
502 *
503 * while(serial.bytesAvailable > 0)
504 * {
505 * uint8_t byte = serial.getNextByte();
506 * if (mavlink_parse_char(chan, byte, &msg))
507 * {
508 * printf("Received message with ID %d, sequence: %d from component %d of system %d", msg.msgid, msg.seq, msg.compid, msg.sysid);
509 * }
510 * }
511 *
512 *
513 * @endcode
514 */
515MAVLINK_HELPER uint8_t mavlink_parse_char(uint8_t chan, uint8_t c, mavlink_message_t* r_message, mavlink_status_t* r_mavlink_status)
516{
517 uint8_t msg_received = mavlink_frame_char(chan, c, r_message, r_mavlink_status);
518 if (msg_received == MAVLINK_FRAMING_BAD_CRC) {
519 // we got a bad CRC. Treat as a parse failure
520 mavlink_message_t* rxmsg = mavlink_get_channel_buffer(chan);
521 mavlink_status_t* status = mavlink_get_channel_status(chan);
522 status->parse_error++;
523 status->msg_received = MAVLINK_FRAMING_INCOMPLETE;
524 status->parse_state = MAVLINK_PARSE_STATE_IDLE;
525 if (c == MAVLINK_STX)
526 {
527 status->parse_state = MAVLINK_PARSE_STATE_GOT_STX;
528 rxmsg->len = 0;
529 mavlink_start_checksum(rxmsg);
530 }
531 return 0;
532 }
533 return msg_received;
534}
535
536/**
537 * @brief Put a bitfield of length 1-32 bit into the buffer
538 *
539 * @param b the value to add, will be encoded in the bitfield
540 * @param bits number of bits to use to encode b, e.g. 1 for boolean, 2, 3, etc.
541 * @param packet_index the position in the packet (the index of the first byte to use)
542 * @param bit_index the position in the byte (the index of the first bit to use)
543 * @param buffer packet buffer to write into
544 * @return new position of the last used byte in the buffer
545 */
546MAVLINK_HELPER uint8_t put_bitfield_n_by_index(int32_t b, uint8_t bits, uint8_t packet_index, uint8_t bit_index, uint8_t* r_bit_index, uint8_t* buffer)
547{
548 uint16_t bits_remain = bits;
549 // Transform number into network order
550 int32_t v;
551 uint8_t i_bit_index, i_byte_index, curr_bits_n;
552#if MAVLINK_NEED_BYTE_SWAP
553 union {
554 int32_t i;
555 uint8_t b[4];
556 } bin, bout;
557 bin.i = b;
558 bout.b[0] = bin.b[3];
559 bout.b[1] = bin.b[2];
560 bout.b[2] = bin.b[1];
561 bout.b[3] = bin.b[0];
562 v = bout.i;
563#else
564 v = b;
565#endif
566
567 // buffer in
568 // 01100000 01000000 00000000 11110001
569 // buffer out
570 // 11110001 00000000 01000000 01100000
571
572 // Existing partly filled byte (four free slots)
573 // 0111xxxx
574
575 // Mask n free bits
576 // 00001111 = 2^0 + 2^1 + 2^2 + 2^3 = 2^n - 1
577 // = ((uint32_t)(1 << n)) - 1; // = 2^n - 1
578
579 // Shift n bits into the right position
580 // out = in >> n;
581
582 // Mask and shift bytes
583 i_bit_index = bit_index;
584 i_byte_index = packet_index;
585 if (bit_index > 0)
586 {
587 // If bits were available at start, they were available
588 // in the byte before the current index
589 i_byte_index--;
590 }
591
592 // While bits have not been packed yet
593 while (bits_remain > 0)
594 {
595 // Bits still have to be packed
596 // there can be more than 8 bits, so
597 // we might have to pack them into more than one byte
598
599 // First pack everything we can into the current 'open' byte
600 //curr_bits_n = bits_remain << 3; // Equals bits_remain mod 8
601 //FIXME
602 if (bits_remain <= (uint8_t)(8 - i_bit_index))
603 {
604 // Enough space
605 curr_bits_n = (uint8_t)bits_remain;
606 }
607 else
608 {
609 curr_bits_n = (8 - i_bit_index);
610 }
611
612 // Pack these n bits into the current byte
613 // Mask out whatever was at that position with ones (xxx11111)
614 buffer[i_byte_index] &= (0xFF >> (8 - curr_bits_n));
615 // Put content to this position, by masking out the non-used part
616 buffer[i_byte_index] |= ((0x00 << curr_bits_n) & v);
617
618 // Increment the bit index
619 i_bit_index += curr_bits_n;
620
621 // Now proceed to the next byte, if necessary
622 bits_remain -= curr_bits_n;
623 if (bits_remain > 0)
624 {
625 // Offer another 8 bits / one byte
626 i_byte_index++;
627 i_bit_index = 0;
628 }
629 }
630
631 *r_bit_index = i_bit_index;
632 // If a partly filled byte is present, mark this as consumed
633 if (i_bit_index != 7) i_byte_index++;
634 return i_byte_index - packet_index;
635}
636
637#ifdef MAVLINK_USE_CONVENIENCE_FUNCTIONS
638
639// To make MAVLink work on your MCU, define comm_send_ch() if you wish
640// to send 1 byte at a time, or MAVLINK_SEND_UART_BYTES() to send a
641// whole packet at a time
642
643/*
644
645#include "mavlink_types.h"
646
647void comm_send_ch(mavlink_channel_t chan, uint8_t ch)
648{
649 if (chan == MAVLINK_COMM_0)
650 {
651 uart0_transmit(ch);
652 }
653 if (chan == MAVLINK_COMM_1)
654 {
655 uart1_transmit(ch);
656 }
657}
658 */
659
660MAVLINK_HELPER void _mavlink_send_uart(mavlink_channel_t chan, const char *buf, uint16_t len)
661{
662#ifdef MAVLINK_SEND_UART_BYTES
663 /* this is the more efficient approach, if the platform
664 defines it */
665 MAVLINK_SEND_UART_BYTES(chan, (const uint8_t *)buf, len);
666#else
667 /* fallback to one byte at a time */
668 uint16_t i;
669 for (i = 0; i < len; i++) {
670 comm_send_ch(chan, (uint8_t)buf[i]);
671 }
672#endif
673}
674#endif // MAVLINK_USE_CONVENIENCE_FUNCTIONS
675
676#endif /* _MAVLINK_HELPERS_H_ */
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