SpritesMind.Net

Well I ended up here because I wanted to make a "retro style" PC using a 68000, realised it was cheaper to buy second hand Mega Drives than just the CPU, and couldn't bring myself to cannibalise one for the project.

So now I've decided to make a custom RAM/IO expansion cart for the MD (prototype sort of working) and will write an OS for that combination, but was wondering if anyone had attempted this before and if so is there any sort of informal standards I should be following?

Obviously all schematics and code would be open source even though I'm pretty sure only me will care lol.

Mechanical Menace wrote:Well I ended up here because I wanted to make a "retro style" PC using a 68000, realised it was cheaper to buy second hand Mega Drives than just the CPU, and couldn't bring myself to cannibalise one for the project.

So now I've decided to make a custom RAM/IO expansion cart for the MD (prototype sort of working) and will write an OS for that combination, but was wondering if anyone had attempted this before and if so is there any sort of informal standards I should be following?

Obviously all schematics and code would be open source even though I'm pretty sure only me will care lol.

Hello there,

yes, 68K in any form can be a bit pricey these days. Plus you'd need to be very sure that your Clock-Circuit is stable and that would require a Scope at the very least.

I shall send you a message as I am actually working on something fairly similar.

Cheers,

Minty.

Mechanical Menace wrote: realised it was cheaper to buy second hand Mega Drives than just the CPU, and couldn't bring myself to cannibalise one for the project.

I just typed in Motorola 68000 on ebay. The first listing I saw was for $3.39 + $3.00 shipping. I don't think you can get a sega genesis for cheaper than that.

sega16 wrote:

Mechanical Menace wrote: realised it was cheaper to buy second hand Mega Drives than just the CPU, and couldn't bring myself to cannibalise one for the project.

I just typed in Motorola 68000 on ebay. The first listing I saw was for $3.39 + $3.00 shipping. I don't think you can get a sega genesis for cheaper than that.

You can: for free People basically throw old Megadrives away - curse them in way...

Years ago I used to visit trash heaps when I was a student and I once found a 68000 inside a Video Player, I desoldered it any kept it as it was 'valuable' at the time.

MintyTheCat wrote:You can: for free People basically throw old Megadrives away - curse them in way...

Definitely not here ! Megadrive is almost 20e minimum now.

Stef wrote:

MintyTheCat wrote:You can: for free People basically throw old Megadrives away - curse them in way...

Definitely not here ! Megadrive is almost 20e minimum now.

Then you should live in the UK or Germany

Tbh this may be due to the UK being heavily urbanised compared to France.

I buy my Megadrives in Berlin and I never pay more than €17 but it is a City and it has lots going on so one can even find old Amiga Computers lying around for low prices.

MintyTheCat wrote:

Stef wrote:

MintyTheCat wrote:You can: for free People basically throw old Megadrives away - curse them in way...

Definitely not here ! Megadrive is almost 20e minimum now.

Then you should live in the UK or Germany

Tbh this may be due to the UK being heavily urbanised compared to France.

I buy my Megadrives in Berlin and I never pay more than €17 but it is a City and it has lots going on so one can even find old Amiga Computers lying around for low prices.

Actually i would say that it is generally more expensive in big city (i'm living close to Paris) than in small one. The thing is that it was very cheap some years ago (between 5e to 15e max) but now it becomes really difficult to find them so they just become more expensive.
The MD sold really well in UK so i guess you can still easily find them.

Stef wrote:

MintyTheCat wrote:

Stef wrote: Definitely not here ! Megadrive is almost 20e minimum now.

Then you should live in the UK or Germany

Tbh this may be due to the UK being heavily urbanised compared to France.

I buy my Megadrives in Berlin and I never pay more than €17 but it is a City and it has lots going on so one can even find old Amiga Computers lying around for low prices.

Actually i would say that it is generally more expensive in big city (i'm living close to Paris) than in small one. The thing is that it was very cheap some years ago (between 5e to 15e max) but now it becomes really difficult to find them so they just become more expensive.
The MD sold really well in UK so i guess you can still easily find them.

Yes, MD was very successful in the UK. Germany it was more Nintendo. Thanks to eBay most simply check that for prices but one can argue to never pay more than the standard rate now. It used to sometimes be a lot worse with sellers asking silly prices. My advice: shop around. Berlin has loads of old shops and half the time the staff do not mind too much so you can get good deals. If the MD is boxed then it is worth more especially if it is a particular version. Ask around too as many people just want to get rid of them - that happened with Prophet and some of my other friends.

Back to subject, I remember talking with devster (http://devster.monkeeh.com/) who quite discouraged me to do so. I can't find back the post, but he noticed to me that even inserting a single charcater in a 500 words document would take quite a long time.
But, we're explorers, aren't we ?
So, as far as I'm concerned, you could definitely build an OS on the top of Megadrive. It already have what glorious computer from the 8bit had (64kB of RAM), a powerful CPU, and something to display (text mode would be a piece of cake).
But man, that is a herculean work !

What you would need is basic OS knowledge : tasks, memory allocation, and IPC. I couldn't advise you more strongly the dinosaur "book" : Operating System Concepts, by Silberschatz, Galvin and Gagne.
AND Micropocessor Systems Design, by Alan Clements. Very good for tasks processing, and a good inward of everything hardware related to 68k

Maybe you could try porting Contiki? It doesn't seem to have a 68000 port yet, but considering it's already able to run on various kinds of 8 bit processors with a few KB of RAM, porting it to a 16 bit platform shouldn't be that difficult.
http://www.contiki-os.org/
http://hitmen.c02.at/html/tools_contiki.html

I suppose it comes down to what type of OS you wished to have.

For me, an OS is usually a Real-Time OS - RTOS. You can see many, many examples of very small Operating-Systems over the Years.

I comes down to what your intentions are:

1. for fun/the hell of it.
2. Real-Time for Gamecode.
3. to recreate that 1980s' feel all over again and have a lovely prompt appear when you turn on the MD Anyone else still love their Commodore-64?

I am working on a Real-Time Os at present but it is meant to be used solely to run Gamecode.

I did my original MD experiments using the MD's Ports set to Serial. I was able to control the MD using a Command-Monitor (which offers basic debug facilities). I then found Prophet's UMDK and began to use UMDK. Once you use UMDK you will find a great increase in your productivity in addition to getting data that you simply could not get without it.

I think that maybe you Blokes are thinking more about having option #3 so why not make a nice little Interpretor for commands and then make a BASIC Interpretor or something like that? Then add on a Keyboard maybe and you should be happy reliving your Childhoods

haroldoop wrote:Maybe you could try porting Contiki? It doesn't seem to have a 68000 port yet, but considering it's already able to run on various kinds of 8 bit processors with a few KB of RAM, porting it to a 16 bit platform shouldn't be that difficult.
http://www.contiki-os.org/
http://hitmen.c02.at/html/tools_contiki.html

More than doable - also MINIX might be cool too or even FreeRTOS...

ob1 wrote:Back to subject, I remember talking with devster (http://devster.monkeeh.com/) who quite discouraged me to do so. I can't find back the post, but he noticed to me that even inserting a single charcater in a 500 words document would take quite a long time.
But, we're explorers, aren't we ?
So, as far as I'm concerned, you could definitely build an OS on the top of Megadrive. It already have what glorious computer from the 8bit had (64kB of RAM), a powerful CPU, and something to display (text mode would be a piece of cake).
But man, that is a herculean work !

What you would need is basic OS knowledge : tasks, memory allocation, and IPC. I couldn't advise you more strongly the dinosaur "book" : Operating System Concepts, by Silberschatz, Galvin and Gagne.
AND Micropocessor Systems Design, by Alan Clements. Very good for tasks processing, and a good inward of everything hardware related to 68k

I used to love that book

Have you read the MINIX Book? That is actually more useful as it goes into more detail (second edition at least not the third) about implementation as opposed to simply being about OS Concepts.

For 68K:

Assembly Language and Systems Programming for the M68000 Family by William H. Ford and William Topp (1 Jan 1992) - pretty decent for general 68K reference but nothing OS oriented.

Assembly Language 68000 (PWS Series in Engineering) by Alan Clements (24 Sep 1993) - this is not about the Hardware as given above and focuses just on Software and includes an Example of an OS.

Assembly Language Subroutines for the 68000 von Lance A. Leventhal und F. Cordes von McGraw-Hill Publishing Co. (Januar 1990) - very good to have to see how an experienced Assembly Developer wrote his Routines for most standard stuff.

There are a few others that I can recommend for the 68K too but that should be enough.

MintyTheCat wrote: You can: for free People basically throw old Megadrives away - curse them in way...

Years ago I used to visit trash heaps when I was a student and I once found a 68000 inside a Video Player, I desoldered it any kept it as it was 'valuable' at the time.

Wow you are very lucky. Where I live there are no free consoles.

Interesting idea. I've thought of doing this myself but haven't gotten around to it proper, though you could see the Forth I wrote as a simple operating system.

I could write a proper editor in it, and it almost has cooperative multitasking.