[Nut-upsuser] Unitek UPS 1250xD - megatec_usb driver

[Alexander I. Gordeev]

On Sun, 17 Feb 2008 23:29:36 +0300, Carlos Rodrigues <carlos.efr at mail.telepac.pt> wrote:

> On Feb 17, 2008 7:56 PM, Alexander I. Gordeev <lasaine at lvk.cs.msu.su> wrote:
>> > The best solution would probably to ignore the first couple of failures in
>> > the 'megatec.c' driver, before declaring data stale. Generally speaking,
>> > one should be careful to declare data stale and only do so after a couple
>> > of attempts to read the status (typically three in a row) have failed.
>>
>> I like the idea of solving this in megatec.c. Both serial and usb
>> interfaces could easily fail.
>
> If the driver fails to get any data in the current polling cycle, it
> declares the data as stale until the next cycle. It tried to read the
> data, it got nothing, ergo the current data is stale. I don't agree
> the driver should systematically retry reading the status within a
> polling cycle.
>
> However, if communication failures are a systematic problem over USB,
> the USB layer should deal with it appropriately.
>

Still I concern about the added latency. I can retry after timeout but
it means that ser_send_pace will not return for seconds.

I'd rather add a variable in megatec.c to make user decide the number of
retries before driver declares data stale (0 by default).

-- 
   Alexander