Date   : Tue, 13 Feb 1996 11:52:53 GMT
From   : lamcw <lamcw@...>
Subject: Re: The BBC's Logical, Well-Documented and Non-Perverse Keyboard

Tom Seddon wrote:

;Now, I have another problem. My virtual BBC is now about 33% slower than 
;a real BBC, on a 486dx2-80. After I've done the obvious optimisations 
;(update VIA clocks every X cycles, that sort of thing), if the speed 
;isn't up to scratch what do people suggest?


Here are a few nice tricks.

1) Use a big SWITCH statement as the heart of your 6502 emulation.

2) Go into a tight loop for say 50 opcodes, then drop out to update
counters, check IRQs etc. This may horrify some purists but I found
this essential to get good performance.

3) Draw the screen every x frames, e.g. 5 for instance.

As a result, MacBeebEm flies on a PowerMac reaching real beeb speed
with a very reasonable frame rate.


Chris Lam,
MacBeebEm Keeper.