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RE: dependency on rs_init

To: linux-mips@fnet.fr
Subject: RE: dependency on rs_init
From: Harald Koerfgen <harald.koerfgen@netcologne.de>
Date: Thu, 27 Aug 1998 19:19:28 +0200 (MEST)
In-reply-to: <Pine.SV4.3.91.980827132232.9499A-100000@mech>
Organization: none
Reply-to: "Harald Koerfgen" <harald.koerfgen@netcologne.de>
Sender: harry@franz.no.dom
Hi,

On 27-Aug-98 Gleb O. Rajko wrote:
> 
> 
> On Wed, 26 Aug 1998, Harald Koerfgen wrote:
> 
>> The other one is using the PROM routines (works on all DECstations). This is
>> what promcon.c in arch/mips/dec is for and is intended as a temporary
>> solution until we have charakter device drivers to use as console devices
>> for
>> all DECstations. 
> 
> Why temporary solution ? My experience shows prom console is good 
> enough to have it permanently. It's bug free, the code is small, higher 
> console code allows to emulate linux-like terminal on top of prom console.
> I would recommend to look at SPARC/Linux code beginning from 2.1.109 
> (according to vger cvs tree, I don't know what is Linus' version that 
> corresponds to). Around this version console stuff was rewritten and became 
> more clear. Now, SPARC/Linux allows to have several consoles: prom, 
> sbus and ATI Mach (available only on UltraSparc). There are also
> run-time options to select, something like console=prom.
> 
> Regards,
> Gleb.

I'd like to see this as a temporary solution because of different reasons:

o The DECstation PROM routines are slow like hell. I don't have exact
measurements at hand, but using the native serial console code seems to be 2-3
times faster.

o The DECstation PROM routines aren't very stable. Printing debugging messages
in exception routines is a no go.

o The DECstation PROM routines are blocking.

o The memory range from 0x80000000 to 0x80030000 is reserved for PROM routines
on DECstations. When the kernel itself doesn't use any PROM routines, the
kernel can be moved to 0x80000000 after loading. This gives us 192KB memory for
free :-).
 
---
Regards,
Harald

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