From 70b875aeb621ef7c24a17e3dd563265456b736b7 Mon Sep 17 00:00:00 2001 From: Lorenz Meier Date: Sat, 22 Feb 2014 15:31:01 +0100 Subject: Added safelink protocol infrastructure - not doing much yet. --- src/modules/px4iofirmware/safelink.c | 163 +++++++++++++++++++++++++++++++++++ 1 file changed, 163 insertions(+) create mode 100644 src/modules/px4iofirmware/safelink.c (limited to 'src/modules/px4iofirmware/safelink.c') diff --git a/src/modules/px4iofirmware/safelink.c b/src/modules/px4iofirmware/safelink.c new file mode 100644 index 000000000..f5c91d0fa --- /dev/null +++ b/src/modules/px4iofirmware/safelink.c @@ -0,0 +1,163 @@ +/**************************************************************************** + * + * Copyright (c) 2012-2014 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 safelink.c + * + * Serial protocol encoder / decoder for the + * simple redundancy protocol (SRP) + */ + +#include + +#include +#include +#include +#include + +#include +#include "px4io.h" + +#define SAFELINK_FRAME_SIZE (2 + 2 * PX4IO_SERVO_COUNT + 2) +#define SAFELINK_STX1 0xFA +#define SAFELINK_STX2 0x01 /**< version */ + +static int safelink_fd = -1; + +static hrt_abstime last_rx_time; +static hrt_abstime last_frame_time; + +static uint8_t frame[SAFELINK_FRAME_SIZE]; + +static unsigned partial_frame_count; + +unsigned safelink_frame_drops; + +static bool safelink_decode(hrt_abstime frame_time, uint16_t *values, uint16_t *num_values, bool *failsafe, uint16_t max_channels); + +int +safelink_init(int fd) +{ + safelink_fd = fd; + return OK; + + r_safelink_count = 0; +} + +void +safelink_output(uint16_t *values, uint16_t num_values) +{ + uint8_t buf[SAFELINK_FRAME_SIZE]; + buf[0] = SAFELINK_STX1; + buf[1] = SAFELINK_STX2; + + for (unsigned i = 0; (i < num_values) && (i < PX4IO_SERVO_COUNT); i++) { + uint8_t *dp = &buf[2 + (2 * i)]; + dp[0] = values[i] >> 8; + dp[1] = values[i]; + } + + buf[SAFELINK_FRAME_SIZE - 2] = 0x11; + buf[SAFELINK_FRAME_SIZE - 1] = 0xFF; +} + +bool +safelink_input(uint16_t *values, uint16_t *num_values, bool *failsafe, uint16_t max_channels) +{ + ssize_t ret; + hrt_abstime now; + bool decode_ret = false; + + /* + * The S.BUS protocol doesn't provide reliable framing, + * so we detect frame boundaries by the inter-frame delay. + * + * The minimum frame spacing is 7ms; with 25 bytes at 100000bps + * frame transmission time is ~2ms. + * + * We expect to only be called when bytes arrive for processing, + * and if an interval of more than 3ms passes between calls, + * the first byte we read will be the first byte of a frame. + * + * In the case where byte(s) are dropped from a frame, this also + * 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) > 3000) { + if (partial_frame_count > 0) { + safelink_frame_drops++; + partial_frame_count = 0; + } + } + + /* + * Fetch bytes, but no more than we would need to complete + * the current frame. + */ + ret = read(safelink_fd, &frame[partial_frame_count], SAFELINK_FRAME_SIZE - partial_frame_count); + + /* if the read failed for any reason, just give up here */ + if (ret < 1) + return false; + + if (partial_frame_count < SAFELINK_FRAME_SIZE) + decode_ret = false; + + safelink_decode(now, values, num_values, failsafe, max_channels); + + /* return false as default */ + return decode_ret; +} + +static bool safelink_decode(hrt_abstime frame_time, uint16_t *values, uint16_t *num_values, bool *failsafe, uint16_t max_channels) +{ + /* check frame boundary markers to avoid out-of-sync cases */ + if ((frame[0] != SAFELINK_STX1) || frame[1] != SAFELINK_STX2) { + safelink_frame_drops++; + return false; + } + + /* XXX check checksum here */ + + + /* if we make it down here, we have valid data */ + last_frame_time = frame_time; + + for (unsigned i = 0; (i < max_channels) && (i < PX4IO_SERVO_COUNT); i++) { + uint8_t *dp = &frame[2 + (2 * i)]; + values[i] = (dp[0] << 8) | dp[1]; + } +} + -- cgit v1.2.3