[Xastir] NMEA v2.1 GSA Sentences case very high CPU load

[Jeff Laughlin]

Got another one :)

I'm using a Magellan SporTrak Map GPS unit. It support 3 types of NMEA output,

v1.5 APA
v1.5 XTE
v2.1 GSA

I'm not honestly sure what the difference is between the two v1.5 settings, 
their sentences appear to be identical. Here is a quick sample, it spits 
out these two sentences once per second:
$GPGLL,4356.22,N,07236.22,W
$GPVTG,000,T,000,M,00.0,N,00.0,K

The v2.1 setting outputs many more sentences on each cycle. Every second it 
outputs something that looks like:
$GPGGA,001925.50,4356.2211,N,07236.2243,W,1,05,6.1,00425,M,,,,*3B
$GPRMC,001925.50,A,4356.2211,N,07236.2243,W,00.0,000.0,060303,15,W*4D
$GPGSA,A,3,18,15,23,06,17,,,,,,,,09.1,06.1,06.7*00
$GPGSV,3,1,10,26,79,139,,29,69,068,,17,53,309,36,23,41,279,51*72
$GPGSV,3,2,10,10,33,073,,06,32,223,47,15,19,309,51,18,19,270,53*7B
$GPGSV,3,3,10,08,14,042,,09,05,169,,120,14,114,,122,36,154,*77
$GPGLL,4356.2211,N,07236.2243,W,001926.511,A*2C
$PMGNST,04.03,3,T,427,05.7,+08861,00*40

When the GPS unit is in v2.1 mode, XASTIR and X cause very high CPU loads.

PPC 604e @ 180MHz
load average: 0.37, 0.30, 0.17
%CPU %MEM   TIME COMMAND
41.5 17.3  11:17 X
  1.9 10.8   0:10 xastir
  1.3  2.2   0:14 top
  0.7  0.9   0:04 syslogd
  0.1  1.4   5:14 sshd

When the GPS is in either of the v1.5 modes, it doesn't really generate any 
CPU load. We're talking 0% CPU, so I won't bother pasting it.

I believe the cause of this load is that every second XASTIR prints in the 
status line "Got GGA String" then "Got RMC String". It probably shouldn't 
print those status strings.

So, why not just use the v1.5 modes? There are two good reasons.
1: The v1.5 modes do not output altitude.
2: My TH-D7a requires v2.1

So there you have it. The solution is probably as simple as just not 
printing those status strings every time it gets those sentences.
-73, Jeff

=============================================================
Jeffrey M. Laughlin        School  : (802)728-1102
jlaughli at vtc.edu           Home    : (802)878-0496
n1ywb at amsat.org            http://solstice.vtc.edu/~jlaughli/