Re: [Qemu-devel] [PATCH] upgrading emulated UART to 16550A

[Jason Wessel <jason.wessel@windriver.com>]

Stefano Stabellini wrote:
> This patch upgrades the emulated UART to 16550A, the code comes from
> xen-unstable.
> The main improvement was introduced with the following patch and
> subsequent email thread:
>
> http://lists.xensource.com/archives/html/xen-devel/2007-12/msg00129.html
>
> I only made few changes to use qemu_get_clock instead of
> clock_gettime, as Anthony suggested a little while ago.
>
>   

I didn't spend the time to figure out what was wrong, but I thought I'd
try your new port emulation against KGDB which is known to work with
real hardware, as well as the existing 16450 qemu uart support.

For some reason, the initial interrupt if a character comes into the
uart does not seem to get raised, so the kernel routine which handles
the traffic never gets invoked.  It is possible that the that the kgdb
kernel driver has a defect, but this does seem to work on real hardware,
so perhaps it is a timing problem or the qemu emulation is not quite
accurate with respect to the real hardware.

If you like, I can provide you a bzImage and the qemu invocation, such
that you could see the problem first hand.

Jason.