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Acorn Arcade forums: News and features: DGEN - The Mega Drive Emulator
 

DGEN - The Mega Drive Emulator

Posted by Jon Hall on 00:00, 30/10/2000 | , ,
 

Jon Hall takes a look at the DGEN emulator...

This new MegaDrive emulator is excellent, and so easy to set up.But let the author speak:


David McEwen (davidm@argonaut.com):


Well it has finally happened, we have a playable Genesis/Megadriveemulator. This will only run on machines with Risc OS 3.5 upwards andif you have a version prior to 3.7 you will need to have the CallASWImodule - which should be easy enough to find.

This version runs at around 30 - 40 fps, but can vary depending on rom. OK so what have I done to make this playable? I have removed alot of the z80 usage, put in a whole host of Acorn specific optimizations and generally made the code very untidy. There is no sound in the beta (and for speed reasons this will take a whilein being incorporated - 15 fps is not to be sniffed at). No saveram, snapshot (just use a background prog - Frederic Elisei's !ScrDumperdoes the job), no demo support - although this is unimportant.


Feedback/comments/suggestions welcome.


You can download it from : http://www.lizjay.demon.co.uk/david/

What is it ?



DGen is a multi-platform Genesis/Megadrive emulator by Dave@dtmnt.com . This is a pretty solid and compatible beast and will run most roms you can throwat it. The Acorn version is derived from the Linux SDL sources, hugethanks to Joe Groff for suchnice code -> pity I had to go and hack it all to bits for speed!

Why is this release classified as 'a dodgy hack'?



Well I don't like releasing emulators that run at sub 20 fps on aStrongARM (honest),so I have done some tweaks and optimizations to a large portion of thecode -> basically tying stuff heavily to the Acorn platform. However even after this the emulator was barely managing to keep a solid 20 fps. So I have hacked around and removed some of the z80 usage, and thus there is no sound in this version.This makes the code run around 15+ fps quicker, very much worthwhile. I will work on getting the sound in and having speed at some point. Also the lack of some of the z80 functionality may lead to certain roms not working, however I think there is a bug somewhere in the C cpu core, as some games work on the Windows version and not on the non-hacky Acorn one.

What do I need ?



An Risc OS computer (why have you got this otherwise ?)If on Risc OS 3.6 or less CallASWI module. A 320x256x256 mode defined (256 colour definable Mode 13) A rom image (bin or smd, are there any other formats ?) A brain - not essential for some of the games, but actually getting themto run ;-)

OK... So how do I use it ?



Easy peasy (I hope anyway). I haven't written a frontend yet - I hatewriting them, and I thought that speed instead of ease of configurability was the way togo. SinceI chose the filetypes when developing Generator there are 2 types(although it doesn't really matter for DGen), &0d0 and &0d1, just filetype theMegadrive/Genesisroms as either (sorry no icon yet -> lucky you got a DGen icon ;-) ). Thenensure youhave around 3-4MB of free RAM in your next slot and double-click on thefile. Et voila one working Megadrive emulator sans sound.

Are there any other options ?


Why yes there are... the full list are:

-v - version
 
-P - PAL mode
 
-f - frameskip
 
(0/1 is off, -1 is auto, any other value is number to skipeach frame - 1. Ie 2 means display every second frame.
 
-p - activates the Game Genie. It takes a comma-delimited list of Game Genie (ABCD-EFGH) and Hex (123456:ABCD) patches to alter the ROM.For example '-p ATBT-AA32,AY3T-AACL,SCRA-BAX0' loads the Sonic 1 cheats to start with 5 extra lives and make each ring worth 8.

No demo/snapshot/sram saving or loading as yet. Not the priority... are next after the speed issue...

Why did you release this and not Generator?



Generator is still under development, but frankly at the current state of play DGen is far more developed. Once I can get some new source to hand I will work on a port of that, which should run faster than this emulator does. However the code I have doesn't have any z80 emulation in it (and runs only a handful of roms that I have), Increased the compatibility somewhat, but DGen in many respects is lightyears ahead.

This emulator runs too slowly is there any way I can make it go faster?



If you have a processor lower than a StrongARM, upgrade! If you have an SA but not Risc OS 4, use autovcache, or upgrade!
If you have both of the above and have clocked your SA... I'm afraid there's not much I can suggest... wait for a new version, hold on for Imago... or buya Megadrive - they are quite cheap now ;-)

This emulator runs too fast is there any way I can slow it down?



If only...If this does happen please send me not the specs of the machine, but theactual machine ;-)

I have found a rom that doesn't work, or I have found a rom with a bug



Drop me an email davidm@argonaut.com or david@acornemus.freeserve.co.uk both are equally well kept track of atm - with full details of your machine and the rom in question. A description of the bug and if possible whether it happens on another version of the emulator.


DGEN is highly recomended, from Jon's personal experience.


 

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Acorn Arcade forums: News and features: DGEN - The Mega Drive Emulator