serial rxerr

[Andy Green]

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Somebody in the thread at some point said:
| Andy Green wrote:
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|> Somebody in the thread at some point said:
|>
|> |> speed 9600 baud; rows 24; columns 80;
|>
|> | Ok, this is one problem. The other one is the interrupt latency. The
|> | threshold is set on 8 chars
|> | so you have ~800us to get chars from the buffer and it is quite a lot.
|>
|> What are we talking about there because it's unclear.
|>
|> At 9600bps each 10-bit character is about 1ms in transit.
|>
|> The threshold for the FIFO at 8 means that normally, the UART does not
|> make an RX interrupt to the CPU until it has 8 characters.  In the case
|> where <8 characters come, it waits for a timeout and then makes the
|> interrupt anyway.
|>
| Ok I wrong, I'm talking for 115200 but is ~4ms, I missed some :(. The
| problem
| is on 9600 too?

I thought it was 115.2kbps but when I did stty on /dev/ttySAC0 for GSM
connection -- and a whole GUI rootfs was running then so it should talk
to GSM -- it reports it is 9600.

The problem is reported at happening on GSM ttySAC0 so it must be being
reported at 9600 baud presumably.

The only question we can ask is does the symptom disappear when we set
crtscts mode on the tty (and hardware handshaking on the UART then).

If the problem does not go away with hardware handshaking enabled, we
have the wrong idea about the problem.

- -Andy
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