[gpsd-dev] stuck in consume_packets/multipoll loop

[Bernd Ocklin]

Hi,

asking for some advice of how to fix this best or what I am missing. I 
am looking for a solution for my own device driver but its identically 
to a nmea2000 case.

In order to loop forever in gpsd_multipoll()'s for-loop over packet 
fragments you need to have

1. "slow" gpsd host (400MHz embedded)
2. chatty nmea2000 device
3. single-frame CAN transmissions (e.g. PGN

Due to 1. and 2. every nmea2000_get() returns > 0.
Due to 3. every packet is complete, outbuflen > 0.

In gpsd_poll() this qualifies for PACKET_SET. In gpsd_multipoll() this 
means  != NO_DATAIS and & PACKET_SET != 0. Thus gpsd_multipoll() just 
loops and gpsd is locked into the nmea 2000 device.

An ugly hack would obviously be to make every second nmea2000_get() call 
a no-op returning 0. But a simple

/* give other devices a chance */
if (changed & PACKET_SET)
                break;

at the end of the loop fixed the problem for me. Not 100% sure about 
side effects for other cases though.

Bernd