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Re: cyg_io_write & printf
- To: Gary Thomas <gthomas at cambridge dot redhat dot com>
- Subject: Re: [ECOS] cyg_io_write & printf
- From: Wolfram Kattanek <wolfram dot kattanek at imms dot de>
- Date: Wed, 07 Feb 2001 16:13:39 +0100 (MET)
- Cc: Wolfram Kattanek <wolfram dot kattanek at imms dot de>, ecos-discuss at sourceware dot cygnus dot com
- References: <981545501.3a81321da0c3e@imp.imms.de> <3A815DE6.8D4BF0E6@cambridge.redhat.com>
Gary Thomas <gthomas@cambridge.redhat.com>:
> > 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.
But when do they get enabled when using main() or cyg_user_start() without
creating some user threads?
When I put the example code inside a user thread (created in cyg_user_start)
everything seems to work fine. Does that mean that (only) the scheduler enables
interrupts? Can the scheduler also be started from inside main() (via creating
a user thread)? When trying to do so I get the following assertion failure:
ASSERT FAIL: <2>intr.cxx [571] static void Cyg_Interrupt::enable_interrupts()
Am I missing something fundamental about eCos?
> > - 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'
But this doesn't solve the above problems concerning mix of interrupt driven and
polled output or am I wrong about that?
> > - 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?
I'm using an anonymous CVS snapshot from Jan 22 2001. However the "AEB-1 eCos"
string is coded inside the file packages/hal/arm/aeb/current/src/hal_diag.c
which is dated from Jul 4 2000.
Wolfram
--
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