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In order to improve the diagnostics for serial connected devices, I would like to add the possibility to differentiate between errors and timeouts. For the ser_get_char() and ser_get_buf_len() we might do this by changing the return value. For the first, return value -1 would be an error, 0 a timeout and 1 success. The latter could return -1 on error, between 0 and (buflen-1) for a timeout and buflen for success. Unfortunately, the ser_get_line_alert()...

...nd timing out. This is a frequent problem and we want to solve this in a generic way for all drivers and not on a driver-by-driver basis (like you did in the AL175 driver now). Your misconception is that you need to calculate the time spent during the communication. This is not the case. The ser_get_*() functions will return as soon they have read the number of bytes requested or the end character was found, no matter how much time is remaining. The timeout is only there to make sure that if characters are lost or the UPS is disconnected, the driver can break from (usually) upsdrv_upd...