Juma TRX2 & PA100D Deadly Embrace

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Juma TRX2 & PA100D Deadly Embrace

Postby 5B4AIY » 25 Nov 2011 19:34

During my testing and verification of my firmware modifications, I managed to crash the operating systems of both the TRX2 and the PA100D, and these notes may be of interest.

There has been previous mention of a lockup of the PA100D, but I could not find any mention of how it can be provoked. In my case I accidentally had both the TRX2 and the PA100D serial ports set to the TEST mode, and then interconnected them. I powered up the PA100D and then turned the TRX2 on. After about 10 seconds the PA100Ds screen blanked and then displayed pure garbage, followed shortly afterwards by the TRX2 locking up.

The reason is not hard to explain. When either device powers up is sends diagnostic output on its serial port. The PA100D tried to interpret the TRX2s output as serial test commands, and of course some of the characters and sequences might well be valid, but most would not. The valid ones would provoke a response, including an EEPROM dump, but the invalid ones would also provoke an error response.

Naturally the TRX2 will now try and interpret the characters from the PA100D, and these too will provoke a response. This in turn provokes a further response from the PA100D. This situation is known as a "Deadly Embrace".

Eventually the inevitable happens, the sheer blizzard of character exchanges ovewhelm the serial port handlers, interrupts are missed, stack overruns occur, and the O/S crashes. The devices become completely non-responsive, and the only way out is to literally "pull the plug" - power off the power supply.

Fortunately no harm is done, although I did find that some user settings were changed unpredicably, as you might expect. No calibration settings were changed however, and the TRX2 did not go into transmit. So, don't interconnect the TRX2 and PA100D with their serial ports set to TEST!
5B4AIY
 
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