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GCS_MAVLink: document the payload-space macros

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Peter Barker 2020-04-15 09:09:28 +10:00 committed by Peter Barker
parent 6d05ed1eb3
commit 41ada7f8f4
1 changed files with 25 additions and 1 deletions
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26
libraries/GCS_MAVLink/GCS.h
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@ -27,10 +27,34 @@
#define GCS_DEBUG_SEND_MESSAGE_TIMINGS 0
// check if a message will fit in the payload space available
// macros used to determine if a message will fit in the space available.
// important note: despite the names, these messages do NOT check to
// see if the payload will fit in the buffer. They check to see if
// the packed message along with any channel overhead will fit.
// PAYLOAD_SIZE returns the amount of space required to send the
// mavlink message with id id on channel chan. Mavlink2 has higher
// overheads than mavlink1, for example.
#define PAYLOAD_SIZE(chan, id) (unsigned(GCS_MAVLINK::packet_overhead_chan(chan)+MAVLINK_MSG_ID_ ## id ## _LEN))
// HAVE_PAYLOAD_SPACE evaluates to an expression that can be used
// anywhere in the code to determine if the mavlink message with ID id
// can currently fit in the output of _chan.
#define HAVE_PAYLOAD_SPACE(chan, id) (comm_get_txspace(chan) >= PAYLOAD_SIZE(chan, id))
// CHECK_PAYLOAD_SIZE - macro which may only be used within a
// GCS_MAVLink object's methods. It inserts code which will
// immediately return false from the current function if there is no
// room to fit the mavlink message with id id on the current object's
// output
#define CHECK_PAYLOAD_SIZE(id) if (txspace() < unsigned(packet_overhead()+MAVLINK_MSG_ID_ ## id ## _LEN)) return false
// CHECK_PAYLOAD_SIZE2 - macro which inserts code which will
// immediately return false from the current function if there is no
// room to fit the mavlink message with id id on the mavlink output
// channel "chan". It is expecting there to be a "chan" variable in
// scope.
#define CHECK_PAYLOAD_SIZE2(id) if (!HAVE_PAYLOAD_SPACE(chan, id)) return false
// convenience macros for defining which ap_message ids are in which streams: