This article is copied from the Game Show section, page 53 of the July 1997 edition of Acorn User. Reproduced with kind permission. The text on this page is copyright 1997 IDG Media Ltd.

Purpose: to play Elite

Graham Nelson reviews the BBC Micro emulator from Warm Silence

In the May issue of Acorn User I reviewed Warm Silence Software's Z80Em, an emulator for the Sinclair Spectrum. This month it's the turn of 6502Em which revives an earlier generation of Acorns: the BBC Micro Model B, BBC Master, Compact and Acorn Electron - anything except the original Atom.

You might think that Acorn would at least tacitly encourage this, but no: they have an inflexibly petty attitude to distributing their old ROM-based operating systems. The BBC Micro ROM images can only be distributed as part of Acorn's own emulator 65Host. (The best that can be said for 65Host is that it's free.) Warm Silence thus have to supply both 6502Em and 65Host, along with a rather silly program to copy the ROM images from one to the other. Worse, the BBC Master versions can't be distributed at all, so unless you have a real BBC Master you can't emulate on either.

This minor nuisance is really the only negative point to make about 6502Em, Which is remarkably good, fast and robust. The 'Info' window describes its purpose as 'to play Elite', and they're not kidding. Elite was a tour de force of BBC Micro Programming, squeezing an amazing amount out of the hardware, so it makes a good test case.

Emulating the hardware

Elite's display is in two screen modes at once - that is, the top two-thirds use one mode and the bottom third another. This requires exquisitely good timing, with the game altering the screenmode exactly as the monitor's electron beam passes through the two-thirds level of the picture. Anyone who's ever tried this, using the interrupt timer on the 6845 chip, may remember that being approximately right is easy - but the tide mark between the two modes looks choppy, sliding up or down by a few pixel rows as the computation load varies. Not so under 6502Em - the Elite split screen is sharp to the pixel.

Elite sounds good, too, with an authentic mix of peals, white noise and rising tones. The emulator appears to have no trouble imitating 'envelopes', that is, instructions to the BBC sound effects hardware. An extravaganza like Ghouls raises the hair on the back of my neck not because it sounds like a haunted house, but because it sounds so much like a BBC Micro, raised from the silicon grave.

Mode 7 teletext graphics were no problem and sideways scrolling - in which the game landscape scrolls smoothly left to right or vice versa - is also in good working order. I found Rocket Raid a little jumpy, but it probably was on the BBC Micro, too; Planetoid was fine. All in all, the only hardware features not emulated are those which can't sensibly be used: the Tube, the serial interface ULA, the shift lock LED and so on.

Since my StrongARM processor clocks over at about 200 times the speed of the BBC Micro's 6502, I didn't expect any speed problems. Nor were there any. 6502Em is normally configured to emulate at 100 per cent of the BBC Micro speed, which means that on a StrongARM RISC PC it is mostly idle, Cranking it up to 10000 per cent, which really means 'as fast as possible', is to say the least an experience. Snapper ran at just over 12 times normal speed, with the ghosts converging on the player so rapidly that an entire three-life game was over in less than five seconds. Zalaga is a manic blur, and none of my frogs in Hopper ever made it across the road.

Transferring software

How can you get the BBC Mciro programs to run on the emulator? One way is to download them from various Internet archives, which keep everything released by the top dozen or so BBC software houses. If you have old tapes, Warm Silence can supply a simple interface - fro the parallel port to audio in/out plugs - and Tapes, a program able to read BBC, Spectrum, Amstrad, TRS-80, Commodore or Memotech cassettes. Another optional extra is the 6502 Support Pack, with a disassmbler, a de-archiver and a setof hacks into most of the famous games.

Anyone wanting a BBC Micro emulator couldn't do better than 6502Em. Highly recommended.

Product details

Product: 6502Em (BBC Micro emulator)
Supplier: Warm Silience Software
Tel: (0585) 487642
Fax: (01608) 737172
E-mail: [email protected]
WWW: http://www.wss.co.uk/
Price: £15 + VAT or £25 + VAT if bought with Z80Em (Spectrum) emulator
Pros: Fast, Good hardware support, Correct screen effects and sound.
Cons: Doesn't come with ROMs for BBC Master, Compact or Electron

Product: 6502Em Support Pack
Price: £8 + VAT or £15 + VAT if bought with Z80E Support Pack

Product: Tape Support Pack
Price: £5 + VAT including circuit diagram for interface. Interface ready-made at £15 + VAT