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CX2SA > SAT 19.06.05 00:29l 41 Lines 1546 Bytes #999 (0) @ AMSAT
BID : ANS-170.03
Read: GUEST
Subj: AO-51 Configuration
Path: DB0FHN<DB0RGB<DB0AAB<F6KFT<F6KMO<HR1FBB<CX2SA
Sent: 050618/2326Z @:CX2SA.LAV.URY.SA #:63461 [Minas] FBB7.00e $:ANS-170.03
From: CX2SA@CX2SA.LAV.URY.SA
To : SAT@AMSAT
AMSAT News Service Bulletin 170.03
From AMSAT HQ SILVER SPRING, MD.
June 19, 2005
To All RADIO AMATEURS
BID: $ANS-170.03
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 with the letter '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.
[ANS thanks Mike, KE4AZN for the above information]
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