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/****************************************************************************
*
* 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;
}
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