mirror of https://github.com/ArduPilot/ardupilot
71 lines
1.9 KiB
C++
71 lines
1.9 KiB
C++
/*
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support for sending UDP packets on MAVLink packet boundaries.
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*/
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#include <AP_HAL/AP_HAL.h>
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#ifndef HAL_BOOTLOADER_BUILD
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#include <GCS_MAVLink/GCS.h>
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#include "packetise.h"
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/*
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return the number of bytes to send for a packetised connection
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*/
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uint16_t mavlink_packetise(ByteBuffer &writebuf, uint16_t n)
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{
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int16_t b = writebuf.peek(0);
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if (b != MAVLINK_STX_MAVLINK1 && b != MAVLINK_STX) {
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/*
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we have a non-mavlink packet at the start of the
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buffer. Look ahead for a MAVLink start byte, up to 256 bytes
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ahead
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*/
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uint16_t limit = n>256?256:n;
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uint16_t i;
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for (i=0; i<limit; i++) {
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b = writebuf.peek(i);
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if (b == MAVLINK_STX_MAVLINK1 || b == MAVLINK_STX) {
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n = i;
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break;
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}
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}
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// if we didn't find a MAVLink marker then limit the send size to 256
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if (i == limit) {
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n = limit;
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}
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return n;
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}
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// cope with both MAVLink1 and MAVLink2 packets
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uint8_t min_length = (b == MAVLINK_STX_MAVLINK1)?8:12;
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// this looks like a MAVLink packet - try to write on
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// packet boundaries when possible
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if (n < min_length) {
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// we need to wait for more data to arrive
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return 0;
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}
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// the length of the packet is the 2nd byte
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int16_t len = writebuf.peek(1);
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if (b == MAVLINK_STX) {
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// This is Mavlink2. Check for signed packet with extra 13 bytes
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int16_t incompat_flags = writebuf.peek(2);
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if (incompat_flags & MAVLINK_IFLAG_SIGNED) {
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min_length += MAVLINK_SIGNATURE_BLOCK_LEN;
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}
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}
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if (n < len+min_length) {
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// we don't have a full packet yet
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return 0;
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}
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if (n > len+min_length) {
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// send just 1 packet at a time (so MAVLink packets
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// are aligned on UDP boundaries)
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n = len+min_length;
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}
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return n;
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}
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#endif // HAL_BOOTLOADER_BUILD
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