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Diffstat (limited to 'src/modules/systemlib/hx_stream.c')
| -rw-r--r-- | src/modules/systemlib/hx_stream.c | 250 |
1 files changed, 250 insertions, 0 deletions
diff --git a/src/modules/systemlib/hx_stream.c b/src/modules/systemlib/hx_stream.c new file mode 100644 index 000000000..8d77f14a8 --- /dev/null +++ b/src/modules/systemlib/hx_stream.c @@ -0,0 +1,250 @@ +/**************************************************************************** + * + * Copyright (C) 2012 PX4 Development Team. All rights reserved. + * + * Redistribution and use in source and binary forms, with or without + * modification, are permitted provided that the following conditions + * are met: + * + * 1. Redistributions of source code must retain the above copyright + * notice, this list of conditions and the following disclaimer. + * 2. Redistributions in binary form must reproduce the above copyright + * notice, this list of conditions and the following disclaimer in + * the documentation and/or other materials provided with the + * distribution. + * 3. Neither the name PX4 nor the names of its contributors may be + * used to endorse or promote products derived from this software + * without specific prior written permission. + * + * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS + * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT + * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS + * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE + * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, + * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, + * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS + * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED + * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT + * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN + * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE + * POSSIBILITY OF SUCH DAMAGE. + * + ****************************************************************************/ + +/** + * @file hx_stream.c + * + * A simple serial line framing protocol based on HDLC + * with 32-bit CRC protection. + */ + +#include <stdint.h> +#include <stdlib.h> +#include <stdbool.h> +#include <crc32.h> +#include <unistd.h> +#include <errno.h> +#include <string.h> +#include <stdio.h> + +#include "perf_counter.h" + +#include "hx_stream.h" + + +struct hx_stream { + uint8_t buf[HX_STREAM_MAX_FRAME + 4]; + unsigned frame_bytes; + bool escaped; + bool txerror; + + int fd; + hx_stream_rx_callback callback; + void *callback_arg; + + perf_counter_t pc_tx_frames; + perf_counter_t pc_rx_frames; + perf_counter_t pc_rx_errors; +}; + +/* + * Protocol magic numbers, straight out of HDLC. + */ +#define FBO 0x7e /**< Frame Boundary Octet */ +#define CEO 0x7c /**< Control Escape Octet */ + +static void hx_tx_raw(hx_stream_t stream, uint8_t c); +static void hx_tx_raw(hx_stream_t stream, uint8_t c); +static int hx_rx_frame(hx_stream_t stream); + +static void +hx_tx_raw(hx_stream_t stream, uint8_t c) +{ + if (write(stream->fd, &c, 1) != 1) + stream->txerror = true; +} + +static void +hx_tx_byte(hx_stream_t stream, uint8_t c) +{ + switch (c) { + case FBO: + case CEO: + hx_tx_raw(stream, CEO); + c ^= 0x20; + break; + } + + hx_tx_raw(stream, c); +} + +static int +hx_rx_frame(hx_stream_t stream) +{ + union { + uint8_t b[4]; + uint32_t w; + } u; + unsigned length = stream->frame_bytes; + + /* reset the stream */ + stream->frame_bytes = 0; + stream->escaped = false; + + /* not a real frame - too short */ + if (length < 4) { + if (length > 1) + perf_count(stream->pc_rx_errors); + + return 0; + } + + length -= 4; + + /* compute expected CRC */ + u.w = crc32(&stream->buf[0], length); + + /* compare computed and actual CRC */ + for (unsigned i = 0; i < 4; i++) { + if (u.b[i] != stream->buf[length + i]) { + perf_count(stream->pc_rx_errors); + return 0; + } + } + + /* frame is good */ + perf_count(stream->pc_rx_frames); + stream->callback(stream->callback_arg, &stream->buf[0], length); + return 1; +} + +hx_stream_t +hx_stream_init(int fd, + hx_stream_rx_callback callback, + void *arg) +{ + hx_stream_t stream; + + stream = (hx_stream_t)malloc(sizeof(struct hx_stream)); + + if (stream != NULL) { + memset(stream, 0, sizeof(struct hx_stream)); + stream->fd = fd; + stream->callback = callback; + stream->callback_arg = arg; + } + + return stream; +} + +void +hx_stream_free(hx_stream_t stream) +{ + /* free perf counters (OK if they are NULL) */ + perf_free(stream->pc_tx_frames); + perf_free(stream->pc_rx_frames); + perf_free(stream->pc_rx_errors); + + free(stream); +} + +void +hx_stream_set_counters(hx_stream_t stream, + perf_counter_t tx_frames, + perf_counter_t rx_frames, + perf_counter_t rx_errors) +{ + stream->pc_tx_frames = tx_frames; + stream->pc_rx_frames = rx_frames; + stream->pc_rx_errors = rx_errors; +} + +int +hx_stream_send(hx_stream_t stream, + const void *data, + size_t count) +{ + union { + uint8_t b[4]; + uint32_t w; + } u; + const uint8_t *p = (const uint8_t *)data; + unsigned resid = count; + + if (resid > HX_STREAM_MAX_FRAME) + return -EINVAL; + + /* start the frame */ + hx_tx_raw(stream, FBO); + + /* transmit the data */ + while (resid--) + hx_tx_byte(stream, *p++); + + /* compute the CRC */ + u.w = crc32(data, count); + + /* send the CRC */ + p = &u.b[0]; + resid = 4; + + while (resid--) + hx_tx_byte(stream, *p++); + + /* and the trailing frame separator */ + hx_tx_raw(stream, FBO); + + /* check for transmit error */ + if (stream->txerror) { + stream->txerror = false; + return -EIO; + } + + perf_count(stream->pc_tx_frames); + return 0; +} + +void +hx_stream_rx(hx_stream_t stream, uint8_t c) +{ + /* frame end? */ + if (c == FBO) { + hx_rx_frame(stream); + return; + } + + /* escaped? */ + if (stream->escaped) { + stream->escaped = false; + c ^= 0x20; + + } else if (c == CEO) { + /* now escaped, ignore the byte */ + stream->escaped = true; + return; + } + + /* save for later */ + if (stream->frame_bytes < sizeof(stream->buf)) + stream->buf[stream->frame_bytes++] = c; +} |