Date   : Mon, 08 Jan 1996 23:35:18 +0000 (GMT)
From   : James Fidell <james@...>
Subject: Re: VIA queries

Tom Seddon wrote:

> 1. Looking at the source for Xbeeb it only seems to use the 
> non-handshaking port A (at &FE4F) as keyboard input/output. Does the 
> handshaking port A (&FE41, I think) work in the same way as far as 
> the keyboard goes?

The OS never uses &FE41 for testing the keyboard as far as I know.

> I'm not doing the user VIA (apart from timers) yet 
> so the exact difference between handshaking and no handshaking 
> doesn't really bother me.

I wouldn't worry about it for the moment.

> 2. To get the keyboard working, is it sufficient to sort out only
> port A, DDRA, the addressable latch and the CB1 (or is it CB2) IRQ?
> Or will the OS need other bits as well? I seem to remember someone 
> saying it uses the timers for the keyboard repeat, but will it work 
> without them (I just want to get the basic INKEY keyboard scan 
> facility before I get started on anything else).

I'm sure you need some of the timers to get the keyboard working at
all.  And it's the CA2 interrupt you need working.

> And also, what sort of speeds are people getting on their emulators? 
> I'm leaving major optimisations until I've got the thing working, but 
> I'd like to get a general idea of the sort of speed I should be 
> aiming for.

Depending on what's happening (sideways scrolling is slow at the moment,
for example, despite my use of shared memory for the screen image),
Xbeeb v0.3 (out soon :-) runs at about the same speed as a normal Beeb
on my 486DX2-66 with 20Mb RAM running Linux-- faster for some things and
slower for others. I have some planned optimisations which should solve
those problems, however.

James.

-- 
 "Yield to temptation --             | Work: Somewhere at Netcom UK (soon)
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        - Lazarus Long               |              James Fidell