Date   : Mon, 22 Aug 1994 11:22:18 +0000
From   : lamcw <lamcw@...>
Subject: general beeb stuff

"Chris L. Rae" <clr1@...> wrote:

;> try zeroing all the paged I/O memory (&FE00 to &FEFF) before running.
;> this may help you get the 32K memory up. i find that my emulator
;> executes about 270,000 6502 opcodes before the > cursor appears.

;I've zeroed the whole of memory, just in case!

zero these location AFTER you've installed the ROM images. The paged I/O memory
is full of text junk (names of people who worked on the beeb at acorn).

;Ahah! So I was partly right! That's not Eddie "The Eagle" Edwards of 
;ski-jumping fame, is it?  ;-)

if it was, he's obviously wasting his time with sport.


;Well, I've just found a somewhat infuriating bug... my emulator 
;occasionally gets things muddled and writes into the program in memory 
;instead of the BBC memory (ie. the source code!).

best to check that all effective addresses are within 0..65535 for the time
being.


;I have gone through the 100 that SQ posted and my emulator works fine for 
;the whole lot of them. However, it now hangs after displaying "BBC 
;Computer 16K" and "BASIC".

it looks like you've got it working. are you waiting for the > prompt?
if you're trapping OSRDCH you may be able to type in text and get it to
execute something. check AUG on that. otherwise, the machine will just
hang (what else can it do?)

you ought to be getting 32K, most strange.

trap BRK to inform you it's been executed. this is very useful in case
your emulator gets lost in zero ram, which it should never do. BASIC
uses the BRK code to display error messages. this is the only time you
should see it in action (as far as the OS and BASIC are concerned)

i have a complete breakdown of which 6502 opcodes (and how frequently)
are executed during boot up. anyone interested let me know.



;I just thought I'd inform you all about who is on/off the list - I've had 
;mail from one Andrew Gregson in Ireland who has written a complete 6502 
;and partly implemented a 6845 (apparently). I don't know what platform he 
;is writing it on; perhaps he could enlighten us!

i've just about got that far. i've got mode 1 and 7 working with a 6845 CRTC
routine which will closely mimic the real thing. once finished, custom modes
should not prove a problem (e.g. mode 8 in AUG). i've also got editing and
a copy cursor.

***********

Stephen Quan <quan@...> wrote:

; I had to compare with up to the first
;6000 instructions before I could tell I had something wrong with
;SBC and ADC!

SBC is used to compute the execution address of a OSBYTE/WORD. so if things
don't quite work, it could be this. i too had a problem this.



chris lam,
aston university.
u.k.