at91sam9260 on linux 2.6.31 with at91 patchset: UART looses bytes when receiving packets

[Russell King - ARM Linux]

On Sat, Oct 31, 2009 at 03:00:54PM +0100, Stefan Schoenleitner wrote:
> Hi,
> 
> I added some debug code to the atmel_serial.c kernel driver now.
> The result is that the kernel *correctly receives* all bytes from
> the "bad" packet:
> 
> kernel: hexdump(): 30 bytes
> kernel: 0000    61 00 1a 01 01 c0 3c 22 cd 3c 36 4b 13 ae 56 99 .a.....<".<6K..V
> kernel: 0010    00 21 e4 29 84 0d c3 6a 95 17 6f 4d 9f c7       .!.)...j..oM..
> 
> 
> But in the application the 0x13 byte is never received:
> 
> 
> hexdump(): 4 bytes
> 0000	61 00 1a 01                                     a...
> read chunk of 25 bytes
> hexdump(): 25 bytes
> 0000	01 c0 3c 22 cd 3c 36 4b ae 56 99 00 21 e4 29 84 ...<".<6K.V..!.)
> 0010	0a c3 6a 95 17 6f 4d 9f c7                      ..j..oM..
> 
> 
> 
> Is it possible that the byte 0x13 is somehow filtered out ?

0x13 is XOFF.

> If so, why does the same code work then on the PC but not on the ARM board ?
> 
> I suspect that my raw terminal setup is missing something ?
> --------------------------------------------------------------------------
>      // set format 8N1
>     newtio.c_cflag &= ~CSIZE;   // Mask the character size bits
>     newtio.c_cflag &= ~PARENB;
>     newtio.c_cflag &= ~CSTOPB;
>     newtio.c_cflag &= ~CSIZE;
>     newtio.c_cflag |= CS8;      // Select 8 data bits
> 
>     // use hardware flow control (RTC/CTS)
>     newtio.c_cflag |= CRTSCTS;
> 
>     // raw input
>     newtio.c_lflag &= ~(ICANON | ECHO | ECHOE | ISIG);
> 
>     // raw ouput
>     newtio.c_oflag &= ~OPOST;
> 
>     // enable receiver and local mode
>     newtio.c_cflag |= (CLOCAL | CREAD);
> 
>     newtio.c_cc[VTIME]=0;
>     newtio.c_cc[VMIN]=1;

You're not touching the iflags at all, so ixon could be set:

       VSTART (021, DC1, Ctrl-Q) Start character. Restarts output  stopped  by
              the  Stop  character.  Recognized when IXON is set, and then not
              passed as input.

       VSTOP  (023, DC3, Ctrl-S) Stop character. Stop output until Start char-
              acter  typed.   Recognized when IXON is set, and then not passed
              as input.

In any case, there's a far easier way to do this - cfmakeraw().  It'll
avoid bugs such as forgetting to set the iflags correctly.  This
modifies the termios as:

                   termios_p->c_iflag &= ~(IGNBRK|BRKINT|PARMRK|ISTRIP
                                   |INLCR|IGNCR|ICRNL|IXON);
                   termios_p->c_oflag &= ~OPOST;
                   termios_p->c_lflag &= ~(ECHO|ECHONL|ICANON|ISIG|IEXTEN);
                   termios_p->c_cflag &= ~(CSIZE|PARENB);
                   termios_p->c_cflag |= CS8;

If you're also setting the baud rate, you should look at cfsetispeed() and
cfsetospeed() as well.