On Sat, 27 Jun 1998 17:11:28 +0100 (BST), Glynn Clements
<[EMAIL PROTECTED]> wrote:
>
>Rildo Pragana wrote:
>
>> I have tried to make a user-level driver for a home-grown device,
>> interfaced with a serial port. Unfortunately, I couldn't make it answer
>> fast, even if the line is set to 38400 bps. I use termios structures with
>> O_NOBLOCK and select() to get the answer received, but there is a delay of
>> 20ms after the character available on the serial port (as I could measure
>> in an oscilloscope).
>>
>> There is a simple way to program a tiny protocol for doing half-duplex
>> comunication with a faster response than this? I'm aware of RTlinux
>> (real-time), but I'm looking for a simpler way. It seems that the problem
>> is a task-switch when I try to read back the result.
>>
>> Perhaps another line discipline could do the job, if I make the protocol
>> in the device driver.
>> Any pointers to such drivers? Other suggestions?
>
>If you need the round-trip-time between receiving data and sending a
>response to be less than 20ms, you'll probably need to either build
>the code into the serial driver, or use a real-time OS.
>
>I'm not sure that RT-Linux would be sufficient. IIRC, there is an
>inherent 10ms lag in the serial driver, regardless of any process
>scheduling issues.
