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Re: Embedded linux serial port

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On 05/26/2021 01:53 PM, pozz wrote:
> I used a simple driver for serial port in Linux with success in many projects, but recently I found an issue with it.
> 
> The scenario is an embedded Linux (running on iMX6) that runs a QT application (that creates a GUI on a touch display) and a C application that communicates over a serial port.
> 
> When QT application starts some complex graphics (I see its CPU load reaching 70-80%), the serial port application stops working correctly.
> After some debugging, I noticed that the bytes really transmitted on the wire aren't correct. It seems one or two bytes are re-transmitted and one-two bytes aren't completely transmitted.
> 
> I suspect my serial port driver has some errors that are triggered only when the CPU is loaded by other processes, but I don't know how to fix them.
> 
> I use O_NONBLOCK flag when opening serial port, but write() always returns a positive number, so I think the byte is correctly moved to the low-level serial port driver and really transmitted... but it isn't always the case.
> 
> If I enable debugging messagin (with DEBUG_SERIAL macro), I always see correct data on stdout, but wrong data on the wire.
> 
> Any hint?
> 
> 
> 
[I didn't read your code]
But here's what I used for transmitting.

static int
send_char (ser * d, char c)
{
  if (d->fd == -1)
    longjmp (d->env, 2);
  ssize_t nbytes = TEMP_FAILURE_RETRY (write (d->fd, &c, 1));
  return !(nbytes == 1);
}

I think the TEMP_FAILURE_RETRY may be important.
but there's about a zillion other flags and iocls wot could be at fault.
So I dont' really know if it helps.

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Embedded linux serial port pozz <pozzugno@gmail.com> - 2021-05-26 13:53 +0200
  Re: Embedded linux serial port Johann Klammer <klammerj@NOSPAM.a1.net> - 2021-05-26 23:52 +0200

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