This article was originally written by Simon N Goodwin for Amiga Format magazine, and is used by permission of the joint copyright holders. It should not be copied any further without written permission. The free emulators mentioned were included on the accompanying CD with the magazine, and are generally available - often in updated form - from this site. The text is as originally submitted to the magazine - which means there are some differences, mostly extra text which was cut to fit into the pages available - with the addition of hyperlinks to new or updated information which has since become available. This approach has been taken to preserve the structure of the original series, while making new information readily available. Simon welcomes comments from readers, care of Tomas Amsrud, who has generously prepared the material for publication on the Internet.

8 bit Apples and Ataris

Simon N Goodwin explores Apple 2
emulators for your Amiga and new
commercial offerings from Blittersoft

No sooner have we tested PCX, the latest from Emplant impresario Jim Drew, than two more emulators arrive from his new company, Microcode Solutions. A][ and ACE emulate eight bit Apple and Atari computers. They're a cut above most PD and shareware emulators, and reasonably priced at Ł19.95 together.

With three free Apple emulators already available, a commercial rival faces competition. David and Stephen Firth's Atari800, reviewed at Christmas, is also PD but very slow, demonstrating that Atari emulation is a tough nut to crack. But if anyone can do it, Microcode Solutions can.

Requirements

The new emulators require at least a 68020 processor, taking advantage of its speed and ability to read misaligned words. They can run in one megabyte of RAM, but prefer two megs, preferably 32 bit fast RAM, for good performance. They use the American keymap rather than the Amiga one, so the quote, hash and at symbols are not where Europeans would expect them. Other keys appear in their usual Amiga positions.

ACE and A][ need Amiga Kickstart 2.04 or better, and do not include the original system ROMs. The Atari emulator has ROM emulation, but to run Apple 2 software you'll need the system and BASIC ROMs from a real Apple, or as a file from CD or the Internet. Sound, colour and mono displays are emulated.

Eight bit Ataris and Apples were produced for a decade from the late seventies and periodically tweaked to boost performance and sales. Microcode Solutions set out to emulate the Atari XL and XE, Apple 2C portable and the 2GS super-Apple,as well as the original machines.

ACE

The Atari Console Emulator - ACE for short - is written by Joe and Mike Fenton. Don't confuse it with the big, slow 'Atari Computer Emulator' written in C for Unix boxes.

On the Amiga, ACE challenges the freeware Atari800, another Unix conversion. ACE makes full use of Amiga sprite and sound hardware, and it shows. Processor emulation is written in machine code rather than C, giving a colossal speed advantage.

In BASIC ACE can loop 10,000 times in 14 seconds at standard settings, compared with 48 seconds for the same test with Atari800 - about thirty per cent of the speed of the real thing, on the fastest Amiga currently available! Keyboard response is instant with ACE, while it lags on Atari800 - although the new release 0.6 is some improvement.

Selecting 'unlimited' speed on a Cyberstorm 68060, ACE runs the same test in under four seconds - three and a half times faster than a real Atari, equivalent to a 6502 at over 6 MHz, and ten times the speed of its freeware rival. ACE delivers full Atari performance on any 68040 Amiga, and performs respectably on a 68030.

Some of the speed of ACE in BASIC comes from passing arithmetic calculations through to the Amiga. Pressing right Amiga and M toggles this, but the difference is not just speed: PRINT 1/9 gives 0.11111111 (correctly) by default, but 0.121951219 thereafter! This suggests a BCD emulation bug, but all is well if you leave the default setting.

Sound and Graphics

ACE is multi-tasking, although like A][ it uses a custom screen so you can't grab images as you could with a standard Amiga window. You can run two at once, and prioritise emulators when displayed and hidden for best multi-tasking performance. The defaults are well chosen.

Like Atari800, ACE supports ECS, but makes best use of the extra colours and improved sprites of AGA. Some Atari programs re-use sprites but ACE does not emulate this correctly, so a horde of horsemen in Necromancer appears as a vertical column, rather than a scattered group. Atari800 gets this right, but at great cost in speed as it renders each sprite into the background.

Qix looks and sounds fine but collisions between the Qix and the player were ignored, ruining the game. Centipede, Adventureland, not-so-super Mario's 1981 Nintendo debut Donkey Kong and the immortal Star Raiders all run perfectly.

Sound emulation is extremely impressive - the best of any eight bit emulator on the Amiga, and practically indistinguishable from the real thing, except that it's in stereo! To manage this, ACE uses all four Amiga sound channels.

Key features

The Amiga function keys emulate START, RESET and so forth on the Atari, with Right Amiga and other keys used to control emulator features. A start -up menu appears on a custom screen when the emulator is launched, and a help screen shows the layout and assignment of Amiga keys.

Configuration is essential. Some Atari disk programs need the 8K of memory occupied by the cartridge slot, while others need BASIC. A few are fussy about the ROM version - ACE supports the original Atari 800 and 400 ROMs, although it has ROM emulation good enough for most games, but not BASIC.

ACE menus feature the XL and XE models as well as the original Atari 400 and 800; the main difference is the amount of memory free for programs. It supports European PAL and American NTSC display formats, which have slightly different timing on an Ataris, as on Amigas.

You can preset these options with Icon tooltypes, or adjust them on a workbench control panel, much like those used with Shapeshifter and PCX. Other controls configure serial, printer, cassette and disk file re -direction to use Amiga hardware or Atari peripherals, via an adapter.

ACE

DISTRIBUTOR: Blittersoft 01908 261466
PRICE: Ł19.95

Speed Impressively fast
Documentation No monitor details
Compatibility Needs some work
Value A lot of work for the price
OVERALL VERDICT: A very promising debut.

83%

Filing

ACE supports up to ten simulated disk drives and re-directs Atari tape CSAVE and CLOAD commands to an Amiga file requester. ACE recognised all the disk, file and cartridge formats I threw at it, but some later releases are incompatible with the Atari 400 ROM it uses or emulates.

If you're confident of your hardware skills you can link the emulator to a real Atari system with a cable from the Amiga parallel port to a couple of the all-purpose Atari controller ports. The documentation includes a circuit diagram and programs in 6502 and 68000 code to manage each end of the net, but you must type the 6502 code into your Atari to get started.

The Atari has four controller ports, but the Amiga has only two. Switched joysticks and CD32 controllers are supported, but unfortunately not analogue joysticks or paddles, although the Amiga mouse can emulate the first two Atari proportional controllers.

Documentation is an decent Amigaguide with a keyboard graphic. I'd prefer printed documentation, with more discussion of compatibility and optional combinations, but got it working with a little trial and error - more related to my dim memories of the original machine than emulator problems. Amiga B calls up an impressive-looking but sadly undocumented built-in 6502 code debugger.

Apple hardware

The Apple 2 was a very early home computer, introduced at the end of 1977. The previous Apple model was a bare board which sold only a handful of units, but the Apple 2 was a much more professional - and expensive - offering, with a neat case, keyboard, internal power supply and expansion slots. The only obvious omission was a TV output, skipped to avoid the need for Federal Communications Authority approval, but readily available from other firms, at least in the USA.

For its day, the Apple had quite remarkable features, including sixteen colours (at a VERY chunky 40 by 48 resolution), high resolution colour graphics (its 280 pixels per line were unprecedented in a 1970s micro, though small beer today) and support for up to 48K RAM.

Apple 'hires' gives six colours from under 8K; a zero byte gives seven black pixels. Adjacent set bits come out white, but odd and even bits in groups of seven appear orange and blue, or purple and green, depending on the setting of the eighth bit! It's MPEG writ tiny; designer Steve Wozniak brilliantly exploited TV display limitations.

Disk drives soon arrived, although the Apple never used a conventional disk controller, relying on Woz's software and an eccentric but effective interface made from cheap 'glue' chips. It is possible to read Apple disks on an Amiga, using the obscure GCR decoding scheme, but it's easier to grab files from the net or CD. The PD utility Disk2File reads Apple DOS 3.3 disks from an Amiga 1020 drive.

Apple disk image files are about 140K in size, accessed at authentically slow pace. Apple2000 comes with AFID, a utility to manipulate files inside a disk image, and reassuringly shows the 'track' number being accessed as it goes along.

Apple Emulators - A][

A][ is Mike Fenton's Apple 2 emulator, bundled with ACE. It can emulate a 48K Apple 2 with a language card and two disk drives, but needs Apple's 12K ROM image. Cassette files go directly to Amiga drives; there's no handler for genuine Apple media. One bit sound is supported.

Apple game paddles are emulated with the mouse or numeric pad. Neat icons appear momentarily when you change these, or the speed of emulation, with function keys. The Amigaguide is skimpy - the monitor is not documented at all - but compatibility is good, and almost everything I tried worked first time.

Free Apples

The greatest challenge to A][ comes from Kevin Krillian's Apple2000, a very competent emulator which has been in free circulation since 1994. At one point Utilities Unlimited demonstrated it as the promised 'Apple 2 module' for Emplant, but that deal fell through.

Apple2000 is on the C64 Sensations Volume 2 CD, with the required ROM image. It's also on Aminet but in that case you must get the ROM separately. Like A][, Apple2000 demands at least a 68020, Workbench 2 and 900K free RAM. I had to disable the 68060 data cache momentarily during start-up to prevent sporadic gurus. Speed can be unlimited or configured from half to double normal, in 50% steps.

The author recommends a 25 MHz 68020 for full speed, and a two-button joystick for compatibility with real Apple sticks. Real Apple joysticks use proportional controllers, rather than Amiga-style switches. If you've already got a proportional controller Apple2000 can take full advantage of it, and this can make all the difference to emulation of some programs.

My stopwatch revealed that Apple2000 was almost four times faster than A][ on simple BASIC, although A][ almost caught up on a hires graphics test. At best Apple2000 ran eight times faster than a real Apple on my Cyberstorm, with good softwarecompatibility.

The old A2

Richard Skrenta's A2 was one of the earliest Apple emulators for the Amiga. It's supplied in source form, with a sample disk image which also works with other Apple emulators.

A2 is entirely written in C, which makes it slow. It incorporates a monitor with useful memory, file and 6502 debugging options, and supports official 6502 and 65C02 instructions, Apple DOS 3.3 and the later ProDOS.

A2 can emulate a 16K language card as well as the main 48K RAM of an original Apple 2, with integer or 'Applesoft' ROMs, but these are not included. There's software to transfer ROMs and disk images. A2 is slow and a bit hard to use, even though key ROM routines are re-written for speed.

AppleOnAmiga is another early effort, this time with source in Modula 2. Like A2, it's incomplete and documentation is scarce - unless you're fluent in Modula - but A2 is free and has some features which might repay the interest of programmers.

Verdicts

A][ works fine but Apple 2000 is better in some respects, and free - see A][ as a 'free gift' with ACE and you won't be disappointed. The menus describe ACE as version 0.1 and it's still early days. It ran half the programs I tried, giving a scrambled screen or messages on the rest. When it works, it's awesome - technically one of the most impressive eight bit emulators on the Amiga, capable of running excellent software even by 1990s standards.

Further development should improve compatibility; I'd like to be able to use analogue joysticks and paddles. For emulator enthusiasts and former Atari eight-bit owners, ACE is already worth getting, and has the makings of a classic emulator in every sense.

A][

DISTRIBUTOR: Blittersoft 01908 261466
PRICE: Free with ACE

Speed Quick 040 required
Documentation Rather skimpy
Compatibility Generally good
Value How can you compete with Ł0?
OVERALL VERDICT: Apple2000 blows it away.

71%

Net Contacts:

Apple 2
http://cie-2.uoregon.edu/~nparker
ftp://ftp.uni-kl.de /pub/apple2

Atari
ftp://atari.archive.umich.edu/atari/8bit/
http://www.signus.demon.co.uk/david/atari/atari.html
ftp://ftp.hackerz.com/hackerz/atari/jellystone/