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Re: Deva interface

From: Marcus Brinkmann
Subject: Re: Deva interface
Date: Tue, 18 Jan 2005 03:29:45 +0100
User-agent: Wanderlust/2.10.1 (Watching The Wheels) SEMI/1.14.6 (Maruoka) FLIM/1.14.6 (Marutamachi) APEL/10.6 Emacs/21.3 (i386-pc-linux-gnu) MULE/5.0 (SAKAKI)

At Tue, 18 Jan 2005 02:45:50 +0100,
"R. Koot" <address@hidden> wrote:
> Hmmm, I problably should have explained why I drew the driver in a 
> double box in my very nice picture.
> +--------+     +--------+     +--------+     +--------+
> |        |     |        | --> |  Deva  | <-> |+------+|
> |  The   | --> | Direct |     +--------+     ||Driver||
> |  Game  |     |  Axe   |                    ||      ||
> |        |     |        | -----------------> |+------+|
> +--------+     +--------+                    +--------+
> It is a a wrapper layer (which would be rather thin on the HURD, a 
> little bit thicker if you wanted to use the same driver on Linux). I 
> don't think a driver should use anything HURD specific or even know Deva 
> exists.

Ok.  Call the wrapper layer deva, drop the deva frame from your
picture, and we have the same mental picture again ;)

At some point everybody just assumed that deva would be a stand alone
task.  I don't know why.  A few days ago it occured to us almost in
passing that we could just as well make the driver framework a library
to deva, or the other way round.

> > make things simpler for us though is that we decided to not focus on
> > support for legacy hardware, but go for the modern stuff first.  So
> > ISA support is optional IMO (does anybody disagree?).
> Unfortunatly until nobdy uses his/her floppy drive anymore, you will 
> need support for ISA DMA. Support for ISA soesn't require any hacks or 
> 'dirty' interfaces. It just requires to make the interfaces a little bit 
> more flexible. Instead of phys_alloc( size ) you would uses a 
> phys_alloc( size, maxaddress, alignment ). You will need this call 
> anyway, becuse when you run the HURD on EMT64 (but not AMD64 due to an 
> IO-MMU I believe) with PCI cards that only support 32-bit memory access 
> you will run into the same problem. Will you require people to throw 
> away their old hardware, because the HURD was 'designed to run on modern 
> hardware'?

All very valid, and true.  I am just saying that if a situation comes
up where it makes a difference, support for legacy hardware may come
with a certain penalty (less optimal paging decisions, whatever).

As for floppie drives, those little buggers are hard to kill!  I guess
they will stay around for a bit longer.  I recently found out the hard
way that a certain proprietary operating system requires a floppy to
allow installation on a SATA drive from scratch.  That was an
interesting experience.

I admit to be a hypocrite on this issue.  ISA can go for all I care,
but take away my serial port and I will bite your arm off.  :)


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