Re: [PATCH v5 2/2] target/xtensa: Use semihosting/syscalls.h

[Max Filippov]

On Wed, Jun 29, 2022 at 3:14 AM Alex Bennée <alex.bennee@linaro.org> wrote:
> Max Filippov <jcmvbkbc@gmail.com> writes:

> > There's no notion of 'serial hardware' for the xtensa-sim, all it has is
> > the three standard stdio file descriptors.
>
> Which are accessed via semihosting calls?

Yes.

> Are they implicitly mapped to
> 3 chardev devices for stdin, stdout and stderr?

In the absence of -serial option they are not mapped.
In the presence of that option they are mapped to the single chardev
that was passed as the parameter of that option.

> > But it was convenient thinking
> > of them as a serial port. I agree that no magic is needed here, but
> > the change shouldn't be quiet eiter, so xtensa-sim should warn (or
> > maybe even quit with an error code) when it sees the -serial option.
>
> If the default chardevs already map to the 3 FDs then perhaps -serial
> should be invalid because it is more explicit to use -chardev to
> redirect the stream you want somewhere else. However I don't see them at
> the moment:
>
>   ➜  ./qemu-system-xtensa -M sim -semihosting -S -display none -monitor stdio
>   QEMU 7.0.50 monitor - type 'help' for more information
>   (qemu) info chardev
>   compat_monitor0: filename=stdio
>   parallel0: filename=vc

Well, that mapping was done by me, manually (grep for sim_console in the
target/xtensa/xtensa-semi.c), so no wonder that parts like this don't work.

-- 
Thanks.
-- Max