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ardupilot/libraries/GCS_MAVLink/GCS_Common.cpp

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// -*- tab-width: 4; Mode: C++; c-basic-offset: 4; indent-tabs-mode: nil -*-
/*
Common GCS MAVLink functions for all vehicle types
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, see <http://www.gnu.org/licenses/>.
*/
#include <GCS.h>
#include <AP_AHRS.h>
extern const AP_HAL::HAL& hal;
uint32_t GCS_MAVLINK::last_radio_status_remrssi_ms;
GCS_MAVLINK::GCS_MAVLINK() :
waypoint_receive_timeout(1000)
{
AP_Param::setup_object_defaults(this, var_info);
}
void
GCS_MAVLINK::init(AP_HAL::UARTDriver *port)
{
GCS_Class::init(port);
if (port == (AP_HAL::BetterStream*)hal.uartA) {
mavlink_comm_0_port = port;
chan = MAVLINK_COMM_0;
initialised = true;
} else if (port == (AP_HAL::BetterStream*)hal.uartC) {
mavlink_comm_1_port = port;
chan = MAVLINK_COMM_1;
initialised = true;
#if MAVLINK_COMM_NUM_BUFFERS > 2
} else if (port == (AP_HAL::BetterStream*)hal.uartD) {
mavlink_comm_2_port = port;
chan = MAVLINK_COMM_2;
initialised = true;
#endif
}
_queued_parameter = NULL;
reset_cli_timeout();
}
uint16_t
GCS_MAVLINK::_count_parameters()
{
// if we haven't cached the parameter count yet...
if (0 == _parameter_count) {
AP_Param *vp;
AP_Param::ParamToken token;
vp = AP_Param::first(&token, NULL);
do {
_parameter_count++;
} while (NULL != (vp = AP_Param::next_scalar(&token, NULL)));
}
return _parameter_count;
}
/**
* @brief Send the next pending parameter, called from deferred message
* handling code
*/
void
GCS_MAVLINK::queued_param_send()
{
if (!initialised || _queued_parameter == NULL) {
return;
}
uint16_t bytes_allowed;
uint8_t count;
uint32_t tnow = hal.scheduler->millis();
// use at most 30% of bandwidth on parameters. The constant 26 is
// 1/(1000 * 1/8 * 0.001 * 0.3)
bytes_allowed = 57 * (tnow - _queued_parameter_send_time_ms) * 26;
if (bytes_allowed > comm_get_txspace(chan)) {
bytes_allowed = comm_get_txspace(chan);
}
count = bytes_allowed / (MAVLINK_MSG_ID_PARAM_VALUE_LEN + MAVLINK_NUM_NON_PAYLOAD_BYTES);
while (_queued_parameter != NULL && count--) {
AP_Param *vp;
float value;
// copy the current parameter and prepare to move to the next
vp = _queued_parameter;
// if the parameter can be cast to float, report it here and break out of the loop
value = vp->cast_to_float(_queued_parameter_type);
char param_name[AP_MAX_NAME_SIZE];
vp->copy_name_token(_queued_parameter_token, param_name, sizeof(param_name), true);
mavlink_msg_param_value_send(
chan,
param_name,
value,
mav_var_type(_queued_parameter_type),
_queued_parameter_count,
_queued_parameter_index);
_queued_parameter = AP_Param::next_scalar(&_queued_parameter_token, &_queued_parameter_type);
_queued_parameter_index++;
}
_queued_parameter_send_time_ms = tnow;
}
/**
* @brief Send the next pending waypoint, called from deferred message
* handling code
*/
void
GCS_MAVLINK::queued_waypoint_send()
{
if (initialised &&
waypoint_receiving &&
waypoint_request_i <= waypoint_request_last) {
mavlink_msg_mission_request_send(
chan,
waypoint_dest_sysid,
waypoint_dest_compid,
waypoint_request_i);
}
}
void GCS_MAVLINK::reset_cli_timeout() {
_cli_timeout = hal.scheduler->millis();
}
void GCS_MAVLINK::send_meminfo(void)
{
#if CONFIG_HAL_BOARD == HAL_BOARD_APM1 || CONFIG_HAL_BOARD == HAL_BOARD_APM2
extern unsigned __brkval;
#else
unsigned __brkval = 0;
#endif
mavlink_msg_meminfo_send(chan, __brkval, hal.util->available_memory());
}
// report power supply status
void GCS_MAVLINK::send_power_status(void)
{
#ifdef CONFIG_ARCH_BOARD_PX4FMU_V2
mavlink_msg_power_status_send(chan,
hal.analogin->board_voltage() * 1000,
hal.analogin->servorail_voltage() * 1000,
hal.analogin->power_status_flags());
#endif
}
// report AHRS2 state
void GCS_MAVLINK::send_ahrs2(AP_AHRS &ahrs)
{
#if AP_AHRS_NAVEKF_AVAILABLE
Vector3f euler;
struct Location loc;
if (ahrs.get_secondary_attitude(euler) && ahrs.get_secondary_position(loc)) {
mavlink_msg_ahrs2_send(chan,
euler.x,
euler.y,
euler.z,
loc.alt*1.0e-2f,
loc.lat,
loc.lng);
}
#endif
}
/*
handle a MISSION_REQUEST_LIST mavlink packet
*/
void GCS_MAVLINK::handle_mission_request_list(AP_Mission &mission, mavlink_message_t *msg)
{
// decode
mavlink_mission_request_list_t packet;
mavlink_msg_mission_request_list_decode(msg, &packet);
// exit immediately if this command is not meant for this vehicle
if (mavlink_check_target(packet.target_system, packet.target_component)) {
return;
}
// reply with number of commands in the mission. The GCS will then request each command separately
mavlink_msg_mission_count_send(chan,msg->sysid, msg->compid, mission.num_commands());
// set variables to help handle the expected sending of commands to the GCS
waypoint_receiving = false; // record that we are sending commands (i.e. not receiving)
waypoint_dest_sysid = msg->sysid; // record system id of GCS who has requested the commands
waypoint_dest_compid = msg->compid; // record component id of GCS who has requested the commands
}
/*
handle a MISSION_REQUEST mavlink packet
*/
void GCS_MAVLINK::handle_mission_request(AP_Mission &mission, mavlink_message_t *msg)
{
AP_Mission::Mission_Command cmd;
// decode
mavlink_mission_request_t packet;
mavlink_msg_mission_request_decode(msg, &packet);
// exit immediately if this command is not meant for this vehicle
if (mavlink_check_target(packet.target_system, packet.target_component)) {
return;
}
// retrieve mission from eeprom
if (!mission.read_cmd_from_storage(packet.seq, cmd)) {
goto mission_item_send_failed;
}
// convert mission command to mavlink mission item packet
mavlink_mission_item_t ret_packet;
memset(&ret_packet, 0, sizeof(ret_packet));
if (!AP_Mission::mission_cmd_to_mavlink(cmd, ret_packet)) {
goto mission_item_send_failed;
}
// set packet's current field to 1 if this is the command being executed
if (cmd.id == (uint16_t)mission.get_current_nav_cmd().index) {
ret_packet.current = 1;
} else {
ret_packet.current = 0;
}
// set auto continue to 1
ret_packet.autocontinue = 1; // 1 (true), 0 (false)
/*
avoid the _send() function to save memory on APM2, as it avoids
the stack usage of the _send() function by using the already
declared ret_packet above
*/
ret_packet.target_system = msg->sysid;
ret_packet.target_component = msg->compid;
ret_packet.seq = packet.seq;
ret_packet.command = cmd.id;
_mav_finalize_message_chan_send(chan,
MAVLINK_MSG_ID_MISSION_ITEM,
(const char *)&ret_packet,
MAVLINK_MSG_ID_MISSION_ITEM_LEN,
MAVLINK_MSG_ID_MISSION_ITEM_CRC);
return;
mission_item_send_failed:
// send failure message
mavlink_msg_mission_ack_send(chan, msg->sysid, msg->compid, MAV_MISSION_ERROR);
}
/*
handle a MISSION_SET_CURRENT mavlink packet
*/
void GCS_MAVLINK::handle_mission_set_current(AP_Mission &mission, mavlink_message_t *msg)
{
// decode
mavlink_mission_set_current_t packet;
mavlink_msg_mission_set_current_decode(msg, &packet);
// exit immediately if this command is not meant for this vehicle
if (mavlink_check_target(packet.target_system,packet.target_component)) {
return;
}
// set current command
if (mission.set_current_cmd(packet.seq)) {
mavlink_msg_mission_current_send(chan, mission.get_current_nav_cmd().index);
}
}
/*
handle a MISSION_COUNT mavlink packet
*/
void GCS_MAVLINK::handle_mission_count(AP_Mission &mission, mavlink_message_t *msg)
{
// decode
mavlink_mission_count_t packet;
mavlink_msg_mission_count_decode(msg, &packet);
// exit immediately if this command is not meant for this vehicle
if (mavlink_check_target(packet.target_system,packet.target_component)) {
return;
}
// start waypoint receiving
if (packet.count > mission.num_commands_max()) {
// send NAK
mavlink_msg_mission_ack_send(chan, msg->sysid, msg->compid, MAV_MISSION_NO_SPACE);
return;
}
// new mission arriving, truncate mission to be the same length
mission.truncate(packet.count);
// set variables to help handle the expected receiving of commands from the GCS
waypoint_timelast_receive = hal.scheduler->millis(); // set time we last received commands to now
waypoint_receiving = true; // record that we expect to receive commands
waypoint_request_i = 0; // reset the next expected command number to zero
waypoint_request_last = packet.count; // record how many commands we expect to receive
waypoint_timelast_request = 0; // set time we last requested commands to zero
}
/*
handle a MISSION_CLEAR_ALL mavlink packet
*/
void GCS_MAVLINK::handle_mission_clear_all(AP_Mission &mission, mavlink_message_t *msg)
{
// decode
mavlink_mission_clear_all_t packet;
mavlink_msg_mission_clear_all_decode(msg, &packet);
// exit immediately if this command is not meant for this vehicle
if (mavlink_check_target(packet.target_system, packet.target_component)) {
return;
}
// clear all waypoints
if (mission.clear()) {
// send ack
mavlink_msg_mission_ack_send(chan, msg->sysid, msg->compid, MAV_RESULT_ACCEPTED);
}else{
// send nack
mavlink_msg_mission_ack_send(chan, msg->sysid, msg->compid, 1);
}
}
/*
handle a MISSION_WRITE_PARTIAL_LIST mavlink packet
*/
void GCS_MAVLINK::handle_mission_write_partial_list(AP_Mission &mission, mavlink_message_t *msg)
{
// decode
mavlink_mission_write_partial_list_t packet;
mavlink_msg_mission_write_partial_list_decode(msg, &packet);
// exit immediately if this command is not meant for this vehicle
if (mavlink_check_target(packet.target_system,packet.target_component)) {
return;
}
// start waypoint receiving
if ((unsigned)packet.start_index > mission.num_commands() ||
(unsigned)packet.end_index > mission.num_commands() ||
packet.end_index < packet.start_index) {
send_text_P(SEVERITY_LOW,PSTR("flight plan update rejected"));
return;
}
waypoint_timelast_receive = hal.scheduler->millis();
waypoint_timelast_request = 0;
waypoint_receiving = true;
waypoint_request_i = packet.start_index;
waypoint_request_last= packet.end_index;
}
/*
return true if a channel has flow control
*/
bool GCS_MAVLINK::have_flow_control(void)
{
switch (chan) {
case MAVLINK_COMM_0:
// assume USB has flow control
return hal.gpio->usb_connected() || hal.uartA->get_flow_control() != AP_HAL::UARTDriver::FLOW_CONTROL_DISABLE;
case MAVLINK_COMM_1:
return hal.uartC->get_flow_control() != AP_HAL::UARTDriver::FLOW_CONTROL_DISABLE;
case MAVLINK_COMM_2:
return hal.uartD != NULL && hal.uartD->get_flow_control() != AP_HAL::UARTDriver::FLOW_CONTROL_DISABLE;
default:
break;
}
return false;
}
/*
handle a request to change stream rate. Note that copter passes in
save==false, as sending mavlink messages on copter on APM2 costs
enough that it can cause flight issues, so we don't want the save to
happen when the user connects the ground station.
*/
void GCS_MAVLINK::handle_request_data_stream(mavlink_message_t *msg, bool save)
{
mavlink_request_data_stream_t packet;
mavlink_msg_request_data_stream_decode(msg, &packet);
if (mavlink_check_target(packet.target_system, packet.target_component))
return;
int16_t freq = 0; // packet frequency
if (packet.start_stop == 0)
freq = 0; // stop sending
else if (packet.start_stop == 1)
freq = packet.req_message_rate; // start sending
else
return;
AP_Int16 *rate = NULL;
switch (packet.req_stream_id) {
case MAV_DATA_STREAM_ALL:
// note that we don't set STREAM_PARAMS - that is internal only
for (uint8_t i=0; i<STREAM_PARAMS; i++) {
if (save) {
streamRates[i].set_and_save_ifchanged(freq);
} else {
streamRates[i].set(freq);
}
}
break;
case MAV_DATA_STREAM_RAW_SENSORS:
rate = &streamRates[STREAM_RAW_SENSORS];
break;
case MAV_DATA_STREAM_EXTENDED_STATUS:
rate = &streamRates[STREAM_EXTENDED_STATUS];
break;
case MAV_DATA_STREAM_RC_CHANNELS:
rate = &streamRates[STREAM_RC_CHANNELS];
break;
case MAV_DATA_STREAM_RAW_CONTROLLER:
rate = &streamRates[STREAM_RAW_CONTROLLER];
break;
case MAV_DATA_STREAM_POSITION:
rate = &streamRates[STREAM_POSITION];
break;
case MAV_DATA_STREAM_EXTRA1:
rate = &streamRates[STREAM_EXTRA1];
break;
case MAV_DATA_STREAM_EXTRA2:
rate = &streamRates[STREAM_EXTRA2];
break;
case MAV_DATA_STREAM_EXTRA3:
rate = &streamRates[STREAM_EXTRA3];
break;
}
if (rate != NULL) {
if (save) {
rate->set_and_save_ifchanged(freq);
} else {
rate->set(freq);
}
}
}
void GCS_MAVLINK::handle_param_request_list(mavlink_message_t *msg)
{
mavlink_param_request_list_t packet;
mavlink_msg_param_request_list_decode(msg, &packet);
if (mavlink_check_target(packet.target_system,packet.target_component)) {
return;
}
#if CONFIG_HAL_BOARD != HAL_BOARD_APM1 && CONFIG_HAL_BOARD != HAL_BOARD_APM2
// send system ID if we can
char sysid[40];
if (hal.util->get_system_id(sysid)) {
send_text(SEVERITY_LOW, sysid);
}
#endif
// Start sending parameters - next call to ::update will kick the first one out
_queued_parameter = AP_Param::first(&_queued_parameter_token, &_queued_parameter_type);
_queued_parameter_index = 0;
_queued_parameter_count = _count_parameters();
}
void GCS_MAVLINK::handle_param_request_read(mavlink_message_t *msg)
{
mavlink_param_request_read_t packet;
mavlink_msg_param_request_read_decode(msg, &packet);
if (mavlink_check_target(packet.target_system,packet.target_component)) {
return;
}
enum ap_var_type p_type;
AP_Param *vp;
char param_name[AP_MAX_NAME_SIZE+1];
if (packet.param_index != -1) {
AP_Param::ParamToken token;
vp = AP_Param::find_by_index(packet.param_index, &p_type, &token);
if (vp == NULL) {
return;
}
vp->copy_name_token(token, param_name, AP_MAX_NAME_SIZE, true);
param_name[AP_MAX_NAME_SIZE] = 0;
} else {
strncpy(param_name, packet.param_id, AP_MAX_NAME_SIZE);
param_name[AP_MAX_NAME_SIZE] = 0;
vp = AP_Param::find(param_name, &p_type);
if (vp == NULL) {
return;
}
}
float value = vp->cast_to_float(p_type);
mavlink_msg_param_value_send_buf(
msg,
chan,
param_name,
value,
mav_var_type(p_type),
_count_parameters(),
packet.param_index);
}
void GCS_MAVLINK::handle_param_set(mavlink_message_t *msg, DataFlash_Class *DataFlash)
{
AP_Param *vp;
enum ap_var_type var_type;
mavlink_param_set_t packet;
mavlink_msg_param_set_decode(msg, &packet);
if (mavlink_check_target(packet.target_system, packet.target_component)) {
return;
}
// set parameter
char key[AP_MAX_NAME_SIZE+1];
strncpy(key, (char *)packet.param_id, AP_MAX_NAME_SIZE);
key[AP_MAX_NAME_SIZE] = 0;
// find the requested parameter
vp = AP_Param::find(key, &var_type);
if ((NULL != vp) && // exists
!isnan(packet.param_value) && // not nan
!isinf(packet.param_value)) { // not inf
// add a small amount before casting parameter values
// from float to integer to avoid truncating to the
// next lower integer value.
float rounding_addition = 0.01;
// handle variables with standard type IDs
if (var_type == AP_PARAM_FLOAT) {
((AP_Float *)vp)->set_and_save(packet.param_value);
} else if (var_type == AP_PARAM_INT32) {
if (packet.param_value < 0) rounding_addition = -rounding_addition;
float v = packet.param_value+rounding_addition;
v = constrain_float(v, -2147483648.0, 2147483647.0);
((AP_Int32 *)vp)->set_and_save(v);
} else if (var_type == AP_PARAM_INT16) {
if (packet.param_value < 0) rounding_addition = -rounding_addition;
float v = packet.param_value+rounding_addition;
v = constrain_float(v, -32768, 32767);
((AP_Int16 *)vp)->set_and_save(v);
} else if (var_type == AP_PARAM_INT8) {
if (packet.param_value < 0) rounding_addition = -rounding_addition;
float v = packet.param_value+rounding_addition;
v = constrain_float(v, -128, 127);
((AP_Int8 *)vp)->set_and_save(v);
} else {
// we don't support mavlink set on this parameter
return;
}
// Report back the new value if we accepted the change
// we send the value we actually set, which could be
// different from the value sent, in case someone sent
// a fractional value to an integer type
mavlink_msg_param_value_send_buf(
msg,
chan,
key,
vp->cast_to_float(var_type),
mav_var_type(var_type),
_count_parameters(),
-1); // XXX we don't actually know what its index is...
if (DataFlash != NULL) {
DataFlash->Log_Write_Parameter(key, vp->cast_to_float(var_type));
}
}
}
void
GCS_MAVLINK::send_text(gcs_severity severity, const char *str)
{
if (severity == SEVERITY_LOW) {
// send via the deferred queuing system
mavlink_statustext_t *s = &pending_status;
s->severity = (uint8_t)severity;
strncpy((char *)s->text, str, sizeof(s->text));
send_message(MSG_STATUSTEXT);
} else {
// send immediately
mavlink_msg_statustext_send(chan, severity, str);
}
}
void
GCS_MAVLINK::send_text_P(gcs_severity severity, const prog_char_t *str)
{
mavlink_statustext_t m;
uint8_t i;
memset(m.text, 0, sizeof(m.text));
for (i=0; i<sizeof(m.text); i++) {
m.text[i] = pgm_read_byte((const prog_char *)(str++));
if (m.text[i] == '\0') {
break;
}
}
if (i < sizeof(m.text)) m.text[i] = 0;
send_text(severity, (const char *)m.text);
}
void GCS_MAVLINK::handle_radio_status(mavlink_message_t *msg, DataFlash_Class &dataflash, bool log_radio)
{
mavlink_radio_t packet;
mavlink_msg_radio_decode(msg, &packet);
// record if the GCS has been receiving radio messages from
// the aircraft
if (packet.remrssi != 0) {
last_radio_status_remrssi_ms = hal.scheduler->millis();
}
// use the state of the transmit buffer in the radio to
// control the stream rate, giving us adaptive software
// flow control
if (packet.txbuf < 20 && stream_slowdown < 100) {
// we are very low on space - slow down a lot
stream_slowdown += 3;
} else if (packet.txbuf < 50 && stream_slowdown < 100) {
// we are a bit low on space, slow down slightly
stream_slowdown += 1;
} else if (packet.txbuf > 95 && stream_slowdown > 10) {
// the buffer has plenty of space, speed up a lot
stream_slowdown -= 2;
} else if (packet.txbuf > 90 && stream_slowdown != 0) {
// the buffer has enough space, speed up a bit
stream_slowdown--;
}
//log rssi, noise, etc if logging Performance monitoring data
if (log_radio) {
dataflash.Log_Write_Radio(packet);
}
}
/*
handle an incoming mission item
*/
void GCS_MAVLINK::handle_mission_item(mavlink_message_t *msg, AP_Mission &mission)
{
mavlink_mission_item_t packet;
uint8_t result = MAV_MISSION_ACCEPTED;
struct AP_Mission::Mission_Command cmd = {};
mavlink_msg_mission_item_decode(msg, &packet);
if (mavlink_check_target(packet.target_system,packet.target_component)) {
return;
}
// convert mavlink packet to mission command
if (!AP_Mission::mavlink_to_mission_cmd(packet, cmd)) {
result = MAV_MISSION_INVALID;
goto mission_ack;
}
if (packet.current == 2) {
// current = 2 is a flag to tell us this is a "guided mode"
// waypoint and not for the mission
handle_guided_request(cmd);
// verify we recevied the command
result = 0;
goto mission_ack;
}
if (packet.current == 3) {
//current = 3 is a flag to tell us this is a alt change only
// add home alt if needed
handle_change_alt_request(cmd);
// verify we recevied the command
result = 0;
goto mission_ack;
}
// Check if receiving waypoints (mission upload expected)
if (!waypoint_receiving) {
result = MAV_MISSION_ERROR;
goto mission_ack;
}
// check if this is the requested waypoint
if (packet.seq != waypoint_request_i) {
result = MAV_MISSION_INVALID_SEQUENCE;
goto mission_ack;
}
// if command index is within the existing list, replace the command
if (packet.seq < mission.num_commands()) {
if (mission.replace_cmd(packet.seq,cmd)) {
result = MAV_MISSION_ACCEPTED;
}else{
result = MAV_MISSION_ERROR;
goto mission_ack;
}
// if command is at the end of command list, add the command
} else if (packet.seq == mission.num_commands()) {
if (mission.add_cmd(cmd)) {
result = MAV_MISSION_ACCEPTED;
}else{
result = MAV_MISSION_ERROR;
goto mission_ack;
}
// if beyond the end of the command list, return an error
} else {
result = MAV_MISSION_ERROR;
goto mission_ack;
}
// update waypoint receiving state machine
waypoint_timelast_receive = hal.scheduler->millis();
waypoint_request_i++;
if (waypoint_request_i >= waypoint_request_last) {
mavlink_msg_mission_ack_send_buf(
msg,
chan,
msg->sysid,
msg->compid,
MAV_MISSION_ACCEPTED);
send_text_P(SEVERITY_LOW,PSTR("flight plan received"));
waypoint_receiving = false;
// XXX ignores waypoint radius for individual waypoints, can
// only set WP_RADIUS parameter
} else {
waypoint_timelast_request = hal.scheduler->millis();
// if we have enough space, then send the next WP immediately
if (comm_get_txspace(chan) - MAVLINK_NUM_NON_PAYLOAD_BYTES >= MAVLINK_MSG_ID_MISSION_ITEM_LEN) {
queued_waypoint_send();
} else {
send_message(MSG_NEXT_WAYPOINT);
}
}
return;
mission_ack:
// we are rejecting the mission/waypoint
mavlink_msg_mission_ack_send_buf(
msg,
chan,
msg->sysid,
msg->compid,
result);
}
// send a message using mavlink, handling message queueing
void GCS_MAVLINK::send_message(enum ap_message id)
{
uint8_t i, nextid;
// see if we can send the deferred messages, if any
while (num_deferred_messages != 0) {
if (!try_send_message(deferred_messages[next_deferred_message])) {
break;
}
next_deferred_message++;
if (next_deferred_message == MSG_RETRY_DEFERRED) {
next_deferred_message = 0;
}
num_deferred_messages--;
}
if (id == MSG_RETRY_DEFERRED) {
return;
}
// this message id might already be deferred
for (i=0, nextid = next_deferred_message; i < num_deferred_messages; i++) {
if (deferred_messages[nextid] == id) {
// its already deferred, discard
return;
}
nextid++;
if (nextid == MSG_RETRY_DEFERRED) {
nextid = 0;
}
}
if (num_deferred_messages != 0 ||
!try_send_message(id)) {
// can't send it now, so defer it
if (num_deferred_messages == MSG_RETRY_DEFERRED) {
// the defer buffer is full, discard
return;
}
nextid = next_deferred_message + num_deferred_messages;
if (nextid >= MSG_RETRY_DEFERRED) {
nextid -= MSG_RETRY_DEFERRED;
}
deferred_messages[nextid] = id;
num_deferred_messages++;
}
}
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