Re: [SeaBIOS] [PATCH] Use dedicated HVM debug io port for Xen

[Julian Pidancet]

On Thu, Jan 5, 2012 at 12:44 AM, Kevin O'Connor  wrote:
> Is the issue that writes to 0x402 are causing an issue on Xen, or just
> that you don't see the debug output?
>
> What's the origin of 0xe9 - is it a "standard" for debug output?  What
> does Xen do today on writes to 0xe9?

Xen has some sort of ring buffer similar to the linux one, that you
can access using the xl dmesg command. Every guest access to the 0xe9
port is trapped by the hypervisor which appends the characters to the
ring buffer. I doubt 0x402 does anything on Xen, aside from beeing
trapped in qemu if configured correctly, but I havn't tried.