Re: Inter-Character Delay

Robin Getz
2008-02-26T16:10:23Z

On Mon 18 Feb 2008 13:36, Robin Getz pondered:
> It is quite common on many industrial serial devices which do not
> support either software or hardware flow control to require a
> Inter-Character delay longer than than the standard one, one and a
> half, or two stop bits.
>
> A device where this long inter character delay is required are devices
> like Point of Sale terminals, and devices that are talking to Modbus
> (Honeywell SI-FTA implements a check on the inter-character gap).
>
> Some hardware manufactures have seen this need, and added it to their
> UART controllers - Atmel's AT32AP7000 has added this and called it a
> "Timeguard" (Don't ask me why). The "timeguard delay" is controlled
> between 0 and 255 Bit Periods.
>
> http://www.atmel.com/dyn/resources/prod_documents/doc32003.pdf
>
> I think I have seen similar things for some ARM devices, and other
> embedded architectures. Today, we have done similar things in the driver
> (on hardware that doesn't support it natively).
>
> I'm not sure that bit periods are the best way to measure things, or
> milliseconds. I guess it really doesn't matter, as long as everyone does
> it the same way - which brings me to my next question:
>
> Does anyone have a good idea of a standard way to expose this to
> userspace?
> - grabbing 8 bits in the termios_p c_oflag isn't going to fit
> - adding a new field in the termios structure seems like overkill
> - adding backdoor ioctls for serial drivers seems like a bad idea.
>
> Thoughts?

ping.

Comments appreciated.

-Robin