Swarm M138 - Messages

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Figure 11: Time Estimates for GPS Date/Time Reference Update

Messages

All messages sent to or from the Hive have an Application ID tag associated with them. The

Application ID can be an arbitrary number from 0 to 64999 (Swarm reserves use of 65000 -

65535), and may be used by the user to organize messages (ex: Application ID 1000 could be

used for device telemetry, 2000 for commands to the device and 3000 for emergencies).

See the $TD - Transmit Data command section in the command directory below for an example

implementation of the Application ID.

Implementation of NMEA checksum in C

uint8_t nmeaChecksum (const char *sz, size_t len)

{

size_t i = 0;

uint8_t cs;

if (sz [0] == '$')

i++;

for (cs = 0; (i < len) && sz [i]; i++)

cs ^= ((uint8_t) sz [i]);

return cs;

}

November 2021 Swarm M138 Modem Manual - Rev 1.00 34/77