UART driver: read function

[Sebastian Huber]

On 20/03/15 11:03, Daniel Krüger wrote:
> Am 20.03.2015 um 10:02 schrieb Sebastian Huber:
>> On 20/03/15 09:42, Daniel Krüger wrote:
>>> Am 06.03.2015 um 11:20 schrieb Sebastian Huber:
>>>>
>>>> I would not use the C stdio for this and instead directly use the 
>>>> POSIX
>>>> read/write. You have to set up the right Termios settings. In case you
>>>> use RTEMS 4.11 I would use the new Termios device interface (see
>>>> rtems_termios_device_install()).
>>>
>>> The code is intended to be platform independent, so I don't want to
>>> change it if not really necessary.
>>
>> will this work on non-POSIX targets at all?
>
> Currently, we use this code under Linux.
>
> This code switches stdin into non-blocking mode via the following 
> sequence:
>
>     tcgetattr(STDIN_FILENO, &oldt);
>     oldf = fcntl(STDIN_FILENO, F_GETFL, 0);
>
>     newt = oldt;
>     newt.c_lflag &= ~(ICANON | ECHO);
>     newf = oldf | O_NONBLOCK;
>
>     tcsetattr(STDIN_FILENO, TCSANOW, &newt);
>     fcntl(STDIN_FILENO, F_SETFL, newf);
>
> Then it tries to read from the input via getchar().
> I must admit this code is a little bit tricky, because it uses 
> ungetc() for the implementation of a Windows kbhit() equivalent.

You already use the Termios functions, so I don't know why you cannot 
use the POSIX read() directly.

>
>>> The interesting thing is, that newlib/libc/stdio/refill.c contains
>>> some "#ifndef __CYGWIN__" which seem to fix the problem under Cygwin.
>>
>> This Cygwin approach seems to be quite a hack. The current FreeBSD
>> variant of refill.c uses the default. How does this work on Linux?
>
> I didn't checked the glibc code, but non-blocking getchar() works as 
> expected.

To me this looks like a glibc vs. BSD libc compatibility issue. I don't 
know if you are in the implementation defined area of the C/POSIX 
standards here.

-- 
Sebastian Huber, embedded brains GmbH

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