Date   : Mon, 08 Aug 1994 10:24:57 EST
From   : Stephen Quan <quan@...>
Subject: Hoping to see something...

Chris Lam writes :

> on a LC475 mac, my emulator runs at the same speed as a real beeb. i've
> got the 100Hz interrupt working, a useable mode 7 display with scrolling
> implemented (updates every second) and i've trapped the OSRDCH routine
> to get key presses. in the meantime i will try to get the cursor keys
> and copy key working to allow some editing, a make shift cursor perhaps
> and then getting the real OS key scan to work probably.

Hi Chris, I am having problems in getting the emulator running.
After some last minute alterations, I believe I have all stack functions
working correctly (PHA,PHP,PLA,PLP,RTS,RTI,JSR).  As far as I know, the
6502 is done, (except for the BCD arithmetic), so I decided to put together
a memory 64K BBC memory image and let my 6502 emulator at it.

On my very crude Mode 7, all I get is a blank screen.  I think I am
missing something severely, or am not emulating the ROMs correctly.

I am curious to know what steps are required in order to 'see' something?
My guess is :

* complete 6502 emulator
* prepare memory image of 64K (BASIC,OS ROMs)
* implement a function to transfer 7C00-8000 to the screen periodically
* start the emulator by jumping to location stored in FFFE.

But what I am curious (as I have not done it yet)

* implement DFS
* implement some keyboard I/O (you mention trapping OSRDCH)

Was it necessary to trap other OS calls?  Does OSWRCH need to be trapped?
-- 
Stephen Quan (quan@...                 ), SysAdmin, Analyst/Programmer.
Centre for Spatial Information Studies, University of Tasmania, Hobart.
GPO BOX 252C, Australia, 7001.  Local Tel: (002) 202898 Fax: (002) 240282
International Callers use +6102 instead of (002).