Re: [ECOS] cyg_io_write & printf

[Gary Thomas <gthomas at cambridge dot redhat dot com>]

Wolfram Kattanek wrote:

> Hello,
>
> I'm playing a little bit with the serial driver functions and came across some
> weird phenomena. Can anyone shed some light on the following questions?
>
> My platform is ARM AEB-1 revision C with one serial port. I'm working with CVS
> sources on a linux host. I configured eCos in the following way: default aeb
> template; enabled CYGDBG_HAL_DIAG_DISABLE_GDB_PROTOCOL, CYGPKG_IO_SERIAL_DEVICES
> and CYGPKG_IO_SERIAL_TTY_TTY1; changed CYGHWR_HAL_ARM_AEB_REVISION to "C".
>
> My test program is:
>
> #include <cyg/io/io.h>
> #include <cyg/io/serialio.h>
> #include <cyg/error/codes.h>
> #include <stdio.h>
>
> void cyg_user_start(void)
> {
>   cyg_uint32 length;
>   Cyg_ErrNo error;
>   char test_msg1[]="This is a test message!\n";
>   cyg_io_handle_t serial_port_handle;
>
>   error = cyg_io_lookup("/dev/ser1", &serial_port_handle);
>   if (error == ENOERR) {
>     length = strlen(&test_msg1[0]);
>     cyg_io_write(serial_port_handle, &test_msg1[0], &length);
>   }
>   printf("Hello eCos world!\n");
> }
>
> I compiled and linked it in the usual (eCos) way and downloaded it to
> the AEB board using a terminal program (minicom; comm parameters:
> 38400 8N1 no Hardware Flow Control and no Software Flow Control).
> Then I started the downloaded program using the AEB monitor program
> and watched the output inside minicom.
>
> In the above configuration of the example program I got the following
> output:
>
> ARM Evaluation Board Boot Monitor 0.01 (19 APR 1998)
> Press ENTER within 2 seconds to stop autoboot
> Boot: download c000
> Ready to download. Use 'transmit' option on terminal emulator to download file.
> Loaded file simple_io_sample.ram.bin at address 0000c000, size = 48028
> Boot: go
>
> AEB-1 eCos
> Hello eCos world!
> This is a test message!
>
> The interesting thing about that output is that the cyg_io_write and printf
> statements seem to output their messages in the "wrong" order!?
>
> More interestingly, if I change cyg_user_start to main then the output
> becomes really weird:
>
> AEB-1 eCos
> This isHaetest lessalo! eCos world!
>
> Both outputs seem to be mixed! The output changes a little bit if I use tty1
> instead of ser1 or \r\n instead of \n but the mixing won't stop.
>

This is happening because 'printf()' uses the diagnostic routines, which use
polling
The 'cyg_io_write()' uses interrupts to drive the port.  Thus, once the 'printf()'
starts, all characters will be displayed at once.  The 'cyg_io_write()' relies on
interrupts
to drive the process.  Getting mixed output is certainly to be expected.

>
> So here are my questions:
>
> - Why is the behavior so different when using main or cyg_user_start?

It depends on when interrupts get enabled.

>
> - Is it possible to use both cyg_io_write and printf when only one physical
>   serial port is available?

Yes, there is an option to get diagnostic output to basically go through 'cyg_io'

>
> - Why the statement order does not reflect the output order in the given
>   example?

Toss of a coin.

>
> - BTW: Is there a config option to turn off the output "AEB-1 eCos"?
>

I'm pretty sure that this has been removed.  Are you using a "release" version
or anonymous CVS?


>
> Any comments are appreciated!
>
> Thanks,
> Wolfram
> --
> Wolfram 'L.A.' Kattanek     Institut fuer Mikroelektronik- und
> Email:       LA@imms.de     Mechatronik-Systeme (IMMS) gGmbH
> Tel: +49 3677 / 6783-55     Langewiesener Str. 22
> Fax: +49 3677 / 6783-38     98693 Ilmenau / Germany
>
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