Date   : Thu, 27 Apr 1995 09:00:05 +0100
From   : Mike Borcherds <borchrds.teaching@...>
Subject: CurrentStateOfMyEmulator

!6502Em - an ARM code BBC B emulator for Acorn RISC OS Machines
Author - Michael Borcherds
Email - borchrds.teaching@...

Features:

o Runs the original unaltered OS 1.2 ROM
o Superb sound emulation
o Full filing system (*SPOOL, *EXEC, OSGBPB etc),
o Page at &E00
o Proper emulation of the keyboard interrupt & keyboard
o Completely redefinable keymap
o Full emulation of both VIAs
o Full emulation of strange screen shapes
o Snapshots
o RISC OS * Commands from within emulator
o Supports paged ROMs
o Desktop frontend (F12 to return)
o Elite works
o Emulation of the DFS directory structure within ADFS
o Option to use RISC OS's OS_ReadC to emulate OSRDCH

Still to do:

o Master 128 emulation
o Caps Lock light
o AMX mouse emulation
o Mid-screen mode/palette changes (maybe)

The Emulation
============

The processor emulated is the 65C12 as in the
Master 128, with the following exceptions:

o Opcodes &07, &4B, &87, &DC emulate the
  respective 6502 undocumented opcodes
o The timing of opcodes when in BCD mode is
  as for the original 6502, not the 65C12
o A few of the opcode timings are not quite
  correct yet
o Opcodes &03 and &23 are used for internal 
  purposes by the emulator
  
NB "Unused" Opcodes are defined to be NOPs
   The extra Rockwell opcodes are not supported

The 6845 CRTC

Registers 1,6,12,13,14,15 are fully emulated
Register 3 is partially emulated
In practical terms, the cursor is the only
part not fully emulated

The Video ULA

Fully emulated, except for "mode 8" and the cursor
Gap modes are displayed without gaps

The 6850 ACIA & Serial ULA

Not Emulated

The Paged ROM Select Register (ROMSEL)

Fully Emulated
Supports ROM or RAM in any of the 16 banks

The 6522 VIAs

The VIAs are fully emulated except for the shift register

The System VIA

Interrupts supported from 6845, keyboard and the two timers
Interrupts from 7002 ADC and light pen not supported
Keyboard, sound and the screen wrap address supported
Keyboard LEDs not supported

The User Via

Interrupts supported from the 2 timers
User & Printer ports not supported

The 7002 ADC

Not emulated

Econet & Disc Hardware

Not Emulated

Tube Hardware

Not Emulated