Date: Tue, 5 Aug 2008 15:57:38 +0200
From: Thiemo Seufer <ths@networkno.de>
Subject: Re: [Qemu-devel] [PATCH] upgrading emulated UART to 16550A
Message-ID: <20080805135738.GC4102@networkno.de>
References: <48985284.9060001@eu.citrix.com>
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In-Reply-To: <48985284.9060001@eu.citrix.com>
Reply-To: qemu-devel@nongnu.org
To: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Ian Jackson <Ian.Jackson@eu.citrix.com>, qemu-devel@nongnu.org

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.
> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
> 
> ---
> 
> 
> diff --git a/hw/serial.c b/hw/serial.c
> index ffd6ac9..f63e62a 100644
> --- a/hw/serial.c
> +++ b/hw/serial.c
> @@ -1,5 +1,5 @@
>  /*
> - * QEMU 16450 UART emulation
> + * QEMU 16550A UART emulation
>   *
>   * Copyright (c) 2003-2004 Fabrice Bellard

I think it needs also an updated copyright notice.

[snip]
> +/* Rate limit serial requests so that e.g. grub on a serial console
> +   doesn't kill dom0.  Simple token bucket.  If we get some actual
> +   data from the user, instantly refil the bucket. */
> +
> +/* How long it takes to generate a token, in nanoseconds. */
> +#define TOKEN_PERIOD 1000000
> +/* Maximum and initial size of token bucket */
> +#define TOKENS_MAX 100000

This token business probably needs a bit more explanation, at a glance
I didn't figure out what it is meant to do (and why the constants above
are good).


Thiemo