fly316/PX4-Autopilot
7
0
Fork 0
mirror of https://gitee.com/mirrors_PX4/PX4-Autopilot.git synced 2026-04-14 10:07:39 +08:00
Code Issues Packages Projects Releases Wiki Activity

sbus: add time-based hardening (only for IO and NuttX)

Browse Source 
Since SBUS does not have CRC, we can use timing information to improve
parsing reliability and reject unexpected bytes.
This commit is contained in:
Beat Küng 2018-12-14 12:11:16 +01:00
parent 4cd8fe0a30
commit eda45b4df2
1 changed files with 34 additions and 21 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

55
src/lib/rc/sbus.cpp
View File

@ -52,6 +52,8 @@
#include "common_rc.h"
#include <drivers/drv_hrt.h>
using namespace time_literals;
#define SBUS_DEBUG_LEVEL 0 /* Set debug output level */
#if defined(__PX4_POSIX_OCPOC)
@ -280,8 +282,21 @@ bool
sbus_input(int sbus_fd, uint16_t *values, uint16_t *num_values, bool *sbus_failsafe, bool *sbus_frame_drop,
uint16_t max_channels)
{
int ret = 1;
hrt_abstime now;
/*
* Fetch bytes, but no more than we would need to complete
* a complete frame.
*/
uint8_t buf[SBUS_FRAME_SIZE * 2];
int ret = read(sbus_fd, &buf[0], SBUS_FRAME_SIZE);
/* if the read failed for any reason, just give up here */
if (ret < 1) {
return false;
}
const hrt_abstime now = hrt_absolute_time();
#ifdef __PX4_NUTTX /* limit time-based hardening to RTOS's where we have reliable timing */
/*
* The S.BUS protocol doesn't provide reliable framing,
@ -298,32 +313,30 @@ sbus_input(int sbus_fd, uint16_t *values, uint16_t *num_values, bool *sbus_fails
* provides a degree of protection. Of course, it would be better
* if we didn't drop bytes...
*/
now = hrt_absolute_time();
if (now - last_rx_time > 3_ms) {
if (partial_frame_count > 0) {
partial_frame_count = 0;
sbus_decode_state = SBUS2_DECODE_STATE_DESYNC;
#if defined(SBUS_DEBUG_LEVEL) && SBUS_DEBUG_LEVEL > 0
printf("SBUS: RESET (TIME LIM)\n");
#endif
}
}
/*
* Fetch bytes, but no more than we would need to complete
* a complete frame.
*/
uint8_t buf[SBUS_FRAME_SIZE * 2];
bool sbus_decoded = false;
ret = read(sbus_fd, &buf[0], SBUS_FRAME_SIZE);
/* if the read failed for any reason, just give up here */
if (ret < 1) {
if (partial_frame_count == 0 && buf[0] != SBUS_START_SYMBOL) {
/* don't bother going through the buffer if we don't get the
* expected start symbol as a first byte */
sbus_decode_state = SBUS2_DECODE_STATE_DESYNC;
return false;
}
#endif /* __PX4_NUTTX */
/*
* Try to decode something with what we got
*/
if (sbus_parse(now, &buf[0], ret, values, num_values, sbus_failsafe,
sbus_frame_drop, &sbus_frame_drops, max_channels)) {
sbus_decoded = true;
}
return sbus_decoded;
return sbus_parse(now, &buf[0], ret, values, num_values, sbus_failsafe,
sbus_frame_drop, &sbus_frame_drops, max_channels);
}
bool