The compromise in SNOOP mode is that it's not doing any buffering between the two (other than the 1-byte transmit register on the SCI) so when a byte comes in on port B it goes out on port A. There's also no locking on port A and the snoop stuff is done in interrupt context, so it could come out in the middle of MONITOR text or something else that's being sent.
Scott Jason KG4WSV wrote: > > > On Mon, Feb 15, 2010 at 4:09 PM, Curt, WE7U <[email protected] > <mailto:curt.we7u%40gmail.com>> wrote: > > > Have a spare serial port on the Atmel? A 'Y' cable coming from the > > GPS is the best way to snoop. I suspect you're probably low on > > ports though as you'll only have one or two. Maybe an 8-pin Atmel > > or PIC to monitor the GPS line, then query it over SPI periodically? > > I was headed down that very road (plan was to bit-bang GPS RX, not > worrying about the occasional lost sentence due to the CPU being > busy), but I'm basically trying to avoid all of that. The ATmega8 > series only has one UART, and that's tied to the T2's A port for the > primary mission. All this GPS stuff is future code to be implemented, > as I currently have too many irons in the fire anyway, but if it works > this way I can go ahead and do a PCB, and add all the features in > software without a PCB redesign. > > In addition to trying to keep it simple, I'm also trying to keep it > small - something along the lines of an OT1+ case would be ideal, > although that's a bit optimistic considering the number of connectors > I need. I'm currently working the tradeoff between number of > connectors and complexity of the cables. :| > > snoop looks perfect, but I wasn't sure if Scott had to make some > compromises that would affect APRS monitor mode to make it happen. > > I don't know much about a "HASP" rig, but it appears to make a TNC+GPS > on a HASP cable out of the T2 A port. snoop would need to be sticky > to make that one real, though, as snoop seems to go off if I hit > enter. > > -Jason > kg4wsv > > ------------------------------------ Yahoo! Groups Links <*> To visit your group on the web, go to: http://groups.yahoo.com/group/tracker2/ <*> Your email settings: Individual Email | Traditional <*> To change settings online go to: http://groups.yahoo.com/group/tracker2/join (Yahoo! ID required) <*> To change settings via email: [email protected] [email protected] <*> To unsubscribe from this group, send an email to: [email protected] <*> Your use of Yahoo! Groups is subject to: http://docs.yahoo.com/info/terms/
