[RFC] Keeping send-delay for all RS232 ttys only?

[Giacinto Cifelli]

Hi Aleksander,

100ms between characters seems excessive.
In general there are the RTS/CTS on the serial line and on the virtual
serial over usb (supported by option and acm drivers) for this.
A stripped down RS232 with only TX/RX/GND could need some delay, but
it is very difficult to guess how much: in this case it would be
better to have it as a parameter.

Some modems require a different delay: between the last answer and the
following command, to have time to output some URCs in between.
At least for Cinterion modems, they don't output URCs between a
command and its response, so they must be given a chance.
The Cinterion ATC guides always specify 100ms, but it turns out that
1-2ms are enough.

Regards,
Giacinto


On Tue, May 4, 2021 at 12:34 AM Aleksander Morgado
<aleksander at aleksander.es> wrote:
>
> Hey Dan & all,
>
> The send-delay property allows us to send the characters in an AT
> command one by one, with some delay in between them. Right now the
> default configuration of the send-delay property is 100ms unless
> explicitly disabled, as it's done in several plugins.
>
> I'm wondering whether it makes sense to keep this logic as it is, or
> change the defaults a bit; e.g. we could keep the logic for plain
> RS232 modems but assume that all USB/PCI modems will be fine without
> the send delay.
>
> What do you all think?
>
> P.S. this comes in the context of this bug, which to me is due to a
> firmware issue or limitation, but anyway:
> https://gitlab.freedesktop.org/mobile-broadband/ModemManager/-/issues/354
>
> --
> Aleksander
> https://aleksander.es
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