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LibrePilot/flight/pios/common/pios_exbus.c

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/**
******************************************************************************
* @file pios_exbus.c
* @author The LibrePilot Project, http://www.librepilot.org Copyright (C) 2015.
* Tau Labs, http://taulabs.org, Copyright (C) 2013
* @addtogroup PIOS PIOS Core hardware abstraction layer
* @{
* @addtogroup PIOS_EXBUS Jeti EX Bus receiver functions
* @{
* @brief Jeti EX Bus receiver functions
*****************************************************************************/
/*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
* or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* for more details.
*
* You should have received a copy of the GNU General Public License along
* with this program; if not, write to the Free Software Foundation, Inc.,
* 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
*/
/* Project Includes */
#include "pios_exbus_priv.h"
#if defined(PIOS_INCLUDE_EXBUS)
#if !defined(PIOS_INCLUDE_RTC)
#error PIOS_INCLUDE_RTC must be used to use EXBUS
#endif
/**
* Based on Jeti EX Bus protocol version 1.21
* Available at http://www.jetimodel.com/en/Telemetry-Protocol/
*/
/* EXBUS frame size and contents definitions */
#define EXBUS_HEADER_LENGTH 4
#define EXBUS_CRC_LENGTH 2
#define EXBUS_MAX_CHANNELS 16
#define EXBUS_OVERHEAD_LENGTH (EXBUS_HEADER_LENGTH + EXBUS_CRC_LENGTH)
#define EXBUS_MAX_FRAME_LENGTH (EXBUS_MAX_CHANNELS * 2 + 10 + EXBUS_OVERHEAD_LENGTH)
#define EXBUS_SYNC_CHANNEL 0x3E
#define EXBUS_SYNC_TELEMETRY 0x3D
#define EXBUS_BYTE_REQ 0x01
#define EXBUS_BYTE_NOREQ 0x03
#define EXBUS_DATA_CHANNEL 0x31
#define EXBUS_DATA_TELEMETRY 0x3A
#define EXBUS_DATA_JETIBOX 0x3B
#define EXBUS_LOW_BAUD_RATE 125000
#define EXBUS_HIGH_BAUD_RATE 250000
#define EXBUS_BAUD_RATE_LIMIT 64
#define EXBUS_FRAME_TIMEOUT 4
#define EXBUS_FAILSAFE_TIMEOUT 64
/* With an Ex.Bus frame rate of 10ms (100Hz) averaging over 20 samples
* gives about a 200ms response.
*/
#define EXBUS_FL_WEIGHTED_AVERAGE 20
/* Forward Declarations */
static int32_t PIOS_EXBUS_Get(uint32_t rcvr_id, uint8_t channel);
static uint16_t PIOS_EXBUS_RxInCallback(uint32_t context,
uint8_t *buf,
uint16_t buf_len,
uint16_t *headroom,
bool *need_yield);
static void PIOS_EXBUS_Supervisor(uint32_t exbus_id);
static uint16_t PIOS_EXBUS_CRC_Update(uint16_t crc, uint8_t data);
static uint8_t PIOS_EXBUS_Quality_Get(uint32_t rcvr_id);
/* Local Variables */
const struct pios_rcvr_driver pios_exbus_rcvr_driver = {
.read = PIOS_EXBUS_Get,
.get_quality = PIOS_EXBUS_Quality_Get,
};
enum pios_exbus_dev_magic {
PIOS_EXBUS_DEV_MAGIC = 0x485355FF,
};
enum pios_exbus_frame_state {
EXBUS_STATE_SYNC,
EXBUS_STATE_REQ,
EXBUS_STATE_LEN,
EXBUS_STATE_PACKET_ID,
EXBUS_STATE_DATA_ID,
EXBUS_STATE_SUBLEN,
EXBUS_STATE_DATA
};
struct pios_exbus_state {
uint16_t channel_data[PIOS_EXBUS_NUM_INPUTS];
uint8_t received_data[EXBUS_MAX_FRAME_LENGTH];
uint8_t receive_timer;
uint8_t failsafe_timer;
uint8_t failsafe_count;
uint8_t byte_count;
uint8_t frame_length;
uint16_t crc;
bool high_baud_rate;
bool frame_found;
float quality;
};
struct pios_exbus_dev {
enum pios_exbus_dev_magic magic;
uint32_t com_port_id;
const struct pios_com_driver *driver;
struct pios_exbus_state state;
};
/* Allocate EXBUS device descriptor */
static struct pios_exbus_dev *PIOS_EXBUS_Alloc(void)
{
struct pios_exbus_dev *exbus_dev;
exbus_dev = (struct pios_exbus_dev *)pios_malloc(sizeof(*exbus_dev));
if (!exbus_dev) {
return NULL;
}
exbus_dev->magic = PIOS_EXBUS_DEV_MAGIC;
return exbus_dev;
}
/* Validate EXBUS device descriptor */
static bool PIOS_EXBUS_Validate(struct pios_exbus_dev *exbus_dev)
{
return exbus_dev->magic == PIOS_EXBUS_DEV_MAGIC;
}
/* Reset channels in case of lost signal or explicit failsafe receiver flag */
static void PIOS_EXBUS_ResetChannels(struct pios_exbus_dev *exbus_dev)
{
struct pios_exbus_state *state = &(exbus_dev->state);
for (int i = 0; i < PIOS_EXBUS_NUM_INPUTS; i++) {
state->channel_data[i] = PIOS_RCVR_TIMEOUT;
}
}
/* Reset EXBUS receiver state */
static void PIOS_EXBUS_ResetState(struct pios_exbus_dev *exbus_dev)
{
struct pios_exbus_state *state = &(exbus_dev->state);
state->receive_timer = 0;
state->failsafe_timer = 0;
state->failsafe_count = 0;
state->high_baud_rate = false;
state->frame_found = false;
state->quality = 0.0f;
PIOS_EXBUS_ResetChannels(exbus_dev);
}
/**
* Check and unroll complete frame data.
* \output 0 frame data accepted
* \output -1 frame error found
*/
static int PIOS_EXBUS_UnrollChannels(struct pios_exbus_dev *exbus_dev)
{
struct pios_exbus_state *state = &(exbus_dev->state);
if (state->crc != 0) {
/* crc failed */
return -1;
}
enum pios_exbus_frame_state exbus_state = EXBUS_STATE_SYNC;
uint8_t *byte = state->received_data;
uint8_t sub_length;
uint8_t n_channels = 0;
uint8_t channel = 0;
while ((byte - state->received_data) < state->frame_length) {
switch (exbus_state) {
case EXBUS_STATE_SYNC:
/* sync byte */
if (*byte == EXBUS_SYNC_CHANNEL) {
exbus_state = EXBUS_STATE_REQ;
} else {
return -1;
}
byte += sizeof(uint8_t);
break;
case EXBUS_STATE_REQ:
/*
* tells us whether the rx is requesting a reply or not,
* currently nothing is actually done with this information...
*/
if (*byte == EXBUS_BYTE_REQ) {
exbus_state = EXBUS_STATE_LEN;
} else if (*byte == EXBUS_BYTE_NOREQ) {
exbus_state = EXBUS_STATE_LEN;
} else {
return -1;
}
byte += sizeof(uint8_t);
break;
case EXBUS_STATE_LEN:
/* total frame length */
exbus_state = EXBUS_STATE_PACKET_ID;
byte += sizeof(uint8_t);
break;
case EXBUS_STATE_PACKET_ID:
/* packet id */
exbus_state = EXBUS_STATE_DATA_ID;
byte += sizeof(uint8_t);
break;
case EXBUS_STATE_DATA_ID:
/* checks the type of data, ignore non-rc data */
if (*byte == EXBUS_DATA_CHANNEL) {
exbus_state = EXBUS_STATE_SUBLEN;
} else {
return -1;
}
byte += sizeof(uint8_t);
break;
case EXBUS_STATE_SUBLEN:
sub_length = *byte;
n_channels = sub_length / 2;
exbus_state = EXBUS_STATE_DATA;
byte += sizeof(uint8_t);
break;
case EXBUS_STATE_DATA:
if (channel < n_channels) {
/* 1 lsb = 1/8 us */
state->channel_data[channel++] = (byte[1] << 8 | byte[0]) / 8;
}
byte += sizeof(uint16_t);
break;
}
}
return 0;
}
/* Update decoder state processing input byte from the stream */
static void PIOS_EXBUS_UpdateState(struct pios_exbus_dev *exbus_dev, uint8_t byte)
{
struct pios_exbus_state *state = &(exbus_dev->state);
if (!state->frame_found) {
if (byte == EXBUS_SYNC_CHANNEL) {
state->frame_found = true;
state->byte_count = 0;
state->frame_length = EXBUS_MAX_FRAME_LENGTH;
state->crc = PIOS_EXBUS_CRC_Update(0, byte);
state->received_data[state->byte_count++] = byte;
}
} else if (state->byte_count < EXBUS_MAX_FRAME_LENGTH) {
state->crc = PIOS_EXBUS_CRC_Update(state->crc, byte);
state->received_data[state->byte_count++] = byte;
if (state->byte_count == 3) {
state->frame_length = byte;
}
if (state->byte_count == state->frame_length) {
uint8_t quality_trend = 0;
if (!PIOS_EXBUS_UnrollChannels(exbus_dev)) {
/* data looking good */
state->failsafe_timer = 0;
state->failsafe_count = 0;
quality_trend = 100;
}
// Calculate quality trend using weighted average of good frames
state->quality = ((state->quality * (EXBUS_FL_WEIGHTED_AVERAGE - 1)) +
quality_trend) / EXBUS_FL_WEIGHTED_AVERAGE;
/* get ready for the next frame */
state->frame_found = false;
}
} else {
state->frame_found = false;
}
}
/* Initialise EX Bus receiver interface */
int32_t PIOS_EXBUS_Init(uint32_t *exbus_id,
const struct pios_com_driver *driver,
uint32_t lower_id)
{
PIOS_DEBUG_Assert(exbus_id);
PIOS_DEBUG_Assert(driver);
struct pios_exbus_dev *exbus_dev;
exbus_dev = (struct pios_exbus_dev *)PIOS_EXBUS_Alloc();
if (!exbus_dev) {
return -1;
}
PIOS_EXBUS_ResetState(exbus_dev);
*exbus_id = (uint32_t)exbus_dev;
/* Set comm driver callback */
(driver->bind_rx_cb)(lower_id, PIOS_EXBUS_RxInCallback, *exbus_id);
if (!PIOS_RTC_RegisterTickCallback(PIOS_EXBUS_Supervisor, *exbus_id)) {
PIOS_DEBUG_Assert(0);
}
exbus_dev->driver = driver;
exbus_dev->com_port_id = lower_id;
return 0;
}
/* Comm byte received callback */
static uint16_t PIOS_EXBUS_RxInCallback(uint32_t context,
uint8_t *buf,
uint16_t buf_len,
uint16_t *headroom,
bool *need_yield)
{
struct pios_exbus_dev *exbus_dev = (struct pios_exbus_dev *)context;
bool valid = PIOS_EXBUS_Validate(exbus_dev);
PIOS_Assert(valid);
/* process byte(s) and clear receive timer */
for (uint8_t i = 0; i < buf_len; i++) {
PIOS_EXBUS_UpdateState(exbus_dev, buf[i]);
exbus_dev->state.receive_timer = 0;
}
/* Always signal that we can accept more data */
if (headroom) {
*headroom = EXBUS_MAX_FRAME_LENGTH;
}
/* We never need a yield */
*need_yield = false;
/* Always indicate that all bytes were consumed */
return buf_len;
}
/**
* Get the value of an input channel
* \param[in] channel Number of the channel desired (zero based)
* \output PIOS_RCVR_INVALID channel not available
* \output PIOS_RCVR_TIMEOUT failsafe condition or missing receiver
* \output >=0 channel value
*/
static int32_t PIOS_EXBUS_Get(uint32_t rcvr_id, uint8_t channel)
{
struct pios_exbus_dev *exbus_dev = (struct pios_exbus_dev *)rcvr_id;
if (!PIOS_EXBUS_Validate(exbus_dev)) {
return PIOS_RCVR_INVALID;
}
/* return error if channel is not available */
if (channel >= PIOS_EXBUS_NUM_INPUTS) {
return PIOS_RCVR_INVALID;
}
/* may also be PIOS_RCVR_TIMEOUT set by other function */
return exbus_dev->state.channel_data[channel];
}
static void PIOS_EXBUS_Change_BaudRate(struct pios_exbus_dev *device)
{
struct pios_exbus_state *state = &(device->state);
if (++state->failsafe_count >= EXBUS_BAUD_RATE_LIMIT) {
state->high_baud_rate = !state->high_baud_rate;
(device->driver->set_baud)(device->com_port_id,
state->high_baud_rate ? EXBUS_HIGH_BAUD_RATE : EXBUS_LOW_BAUD_RATE);
state->failsafe_count = 0;
}
}
/**
* Input data supervisor is called periodically and provides
* two functions: frame syncing and failsafe triggering.
*
* EX.Bus frames come at 20ms or 10ms rate at 125 or 250 kbaud.
* RTC timer is running at 625Hz (1.6ms). So with divider 5 it gives
* 8ms pause between frames which is good for both EX.Bus frame rates.
*
* Data receive function must clear the receive_timer to confirm new
* data reception. If no new data received in 100ms, we must call the
* failsafe function which clears all channels.
*/
static void PIOS_EXBUS_Supervisor(uint32_t exbus_id)
{
struct pios_exbus_dev *exbus_dev = (struct pios_exbus_dev *)exbus_id;
bool valid = PIOS_EXBUS_Validate(exbus_dev);
PIOS_Assert(valid);
struct pios_exbus_state *state = &(exbus_dev->state);
/* waiting for new frame if no bytes were received in 8ms */
if (++state->receive_timer > EXBUS_FRAME_TIMEOUT) {
state->frame_found = false;
state->byte_count = 0;
state->receive_timer = 0;
state->frame_length = EXBUS_MAX_FRAME_LENGTH;
}
/* activate failsafe if no frames have arrived in 102.4ms */
if (++state->failsafe_timer > EXBUS_FAILSAFE_TIMEOUT) {
PIOS_EXBUS_ResetChannels(exbus_dev);
state->failsafe_timer = 0;
state->quality = 0.0f;
PIOS_EXBUS_Change_BaudRate(exbus_dev);
}
}
static uint8_t PIOS_EXBUS_Quality_Get(uint32_t exbus_id)
{
struct pios_exbus_dev *exbus_dev = (struct pios_exbus_dev *)exbus_id;
bool valid = PIOS_EXBUS_Validate(exbus_dev);
PIOS_Assert(valid);
struct pios_exbus_state *state = &(exbus_dev->state);
return (uint8_t)(state->quality + 0.5f);
}
static uint16_t PIOS_EXBUS_CRC_Update(uint16_t crc, uint8_t data)
{
data ^= (uint8_t)crc & (uint8_t)0xFF;
data ^= data << 4;
crc = ((((uint16_t)data << 8) | ((crc & 0xFF00) >> 8))
^ (uint8_t)(data >> 4) ^ ((uint16_t)data << 3));
return crc;
}
#endif /* PIOS_INCLUDE_EXBUS */
/**
* @}
* @}
*/
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