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[SLUG] Serial write problem

I have been working with a single-board computer (TS-7250, using the built-in linux) which, about three times per second, sends 8-byte messages out through COM2 to another device. Very occasionally (it can go 20 hours without failing) a message doesn't all get transmitted. Only 7 of the eight bytes get sent. On these occasions, the status returned by write(2) is "Resource temporarily unavailable".

It seems reasonable to try another write(2) to transmit the eighth byte. However, it crashes without returning. We tried with COM1 and the same thing happened. This is illogical - we are not using handshaking and the UART has no way of knowing what is going on at the other end of the line or even whether there is anything there. I have dumped termios and the control registers immediately before the crash; no corruption or other abnormality is evident.

Before I try a different linux (cut-down debian Potato is available), does anyone have any simpler suggestions?


Jim Donovan