[aprssig] APRS on ECHO

[scott at opentrac.org]

Does anyone know if this address byte has to be contained within the HDLC
frame?  I'm curious if you could send a sequence with FLAG - 'P' - ABORT
before the real frame to wake it up.  Assuming it handles an HDLC abort
properly.  You should still be able to end the wakeup frame with a flag, and
have it get dropped as a runt or failed FCS.

Scott
N1VG 

> -----Original Message-----
> From: aprssig-bounces at lists.tapr.org 
> [mailto:aprssig-bounces at lists.tapr.org] On Behalf Of Jason Winningham
> Sent: Wednesday, June 29, 2005 6:50 AM
> To: TAPR APRS Mailing List
> Subject: [aprssig] APRS on ECHO
> 
> I just noticed this from "AMSAT NEWS SERVICE BULLETIN 177.S1 
> FROM AMSAT HQ SILVER SPRING, MD, JUNE 26, 2005" posted to 
> rec.radio.amateur.space.  I thought I'd post this to the list 
> since APRS via ECHO has been discussed recently.
> 
> -Jason
> kg4wsv
> 
> 
> > From the Satellite Software Development Team:
> >
> > Due to restrictions in the Satellite, there can be no digi 
> > functionality on Echo at this time.
> >
> > Explanation:
> > Random noise from a receiver that is fed through the 
> demodulator and 
> > into the SCC (a sort of smart UART) will cause interrupts 
> to be sent 
> > to the CPU. With Echo having 4 or 5 open receivers the number of 
> > interrupts was enough to cause the CPU difficulties in 
> getting normal 
> > processing done in a timely fashion.  Basically, the CPU 
> was locked up 
> > trying to handle the interrupts. Echo is operating its SCC 
> ports in a 
> > mode that will only pass AX.25 packets beginning with a certain 
> > character, which is called 'block' mode.  This configuration solved 
> > the interrupt problem.  For Echo, with the call sign being "PACB or 
> > PECHO", only packets beginning with the character 'P' can 
> get through 
> > the SCC and generate a CPU interrupt.
> >
> > A digi packet has the call sign of the destination station first, 
> > followed by the satellite (relay) call sign, and then the 
> originator 
> > call sign. Therefore, the digi packet will not get through the SCC
> > unless the destination station call sign begins wit   htheletter'P'.
> >
> > A great deal of effort was put into solving this problem.  This 
> > solution is the only one at the present time that has worked well 
> > enough to implement in the Satellite.
> 
> 
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