[Coco] Mame CoCo 3 emulation questions...

[Andrew Ayers]

Hello all.

After the last message to the list, in regards to using Mame emulation 
for the CoCo 3...well, I had to play with things. So, now I have some 
questions, which I'm sure with a little (or a lot) of digging, I can 
find answers to...but maybe I can get a quicker response here.

First, note that my operating system is a version of Ubuntu 22.04LTS 
(with the latest updates), and my Mame version is 0.220; I am not sure 
if either will matter to any answers, but I thought it best to mention it...

--- Start of Questions ---

1. In the directory where I have my rom zip files, I had an "rgbdos.rom" 
file; I am not sure why I put it there originally, but if I had to 
guess, it's because (IIRC) that is the version of "dos" that I am using 
under VCC to "access" a virtual hard drive I had set up, with "256" 
"floppy drives", for a project I was working on...and I played with it, 
but either couldn't make it work, or made it work in some other manner.

I wanted to see if I could get it to work again, so for my attempt, I 
took my "coco3.zip" file, and dropped the "rgbdos.rom" into it; when I 
ran Mame, it barfed, saying that the image didn't match what it expected.

So I dumped the "disk11.rom", and replaced it with the "rgbdos.rom" 
renamed to "disk11.rom"; this time, when I ran Mame (ie, "mame -w 
coco3") it complained about the file, but loaded it up anyhow, saying it 
might have problems; rgbdos started up, but failed to find a hard drive.

So now I have a couple of questions about this in itself:

a. It seems like Mame does have a "hard coding" of things; renaming the 
file (ie, "coco3rgb.zip", plus the internal files - ie, "coco3.rom" -> 
"coco3rgb.rom", etc) didn't seem to help matters at all; I also noticed 
in the menu (I figured out how to get to it again) seemed to indicate 
some kind of "coco" driver (the emulated machine) - I think it was 
"coco.c"?

b. If I wanted to use an image not recognized normally, does this mean I 
would need to alter and compile a custom Mame, in order to reference the 
new rom zip file (instead of renaming and "faking" it to be 
"coco3.zip")? I mean, that works - but it still shows a "warning error" 
at the start; I could, for example, create a shell script to do the swap 
(or build a new zip file, rename the old one, etc and rename things back 
on exist, yadayada), and run that instead; but that warning looks "janky"...

---

2. Something else I noticed: I couldn't find anywhere in the Mame menu 
system how much memory this emulated CoCo 3 had. Looking at the 
"coco3.ini" file I have, there is a setting called "romsize" (I think 
that's right) - but it isn't set to anything; does it default to 128K 
then? If I set that particular setting to something, would it recognize 
that as the amount of memory? Does it need to be referenced as a "total 
number of bytes" (ie, for 512K it would be set to 524288), or does it 
allow for a "shortcut notation" of some sort (or both)? Also - is there 
a limit to what I can set this to (ie - 2MB? 4MB? 8MB? That is, whatever 
the largest size the CoCo 3 could support by various means; yes, I know 
this means that for best usage, I would need "OS-9", unless I used the 
usual means to access the extra memory - and maybe some "unusual" means 
to access anything over 512K, which I don't know how it was done, but if 
I had to guess, by using the same register(s?) for bank selection, but 
also using the couple of extra "unused/reserved bits" on (well, whatever 
the memory location is in the 64K map - I think it something like $FF## 
where I don't recall offhand what the other 8-bits were).

---

3. Also - am I missing something in the menu system (or elsewhere) that 
would show the amount of total memory (?MEM of course is not it); or 
would it be some kind of CoCo 3 utility I'd have to run (and I would 
assume that most or all of those utilities max out at 512K - except 
perhaps newer utilities, and/or including things under OS-9)?

--- End of Questions ---

Well...that's it for now; thank you for any answers/suggestions.

I'll play around with it some more, and try out any of the community's 
suggestions...but right now it's really just a diversion, as like I 
mentioned before, I don't really use Mame for CoCo emulation, and the 
other emulators I have set up are used rarely, and my actual hardware 
even less (aka, hardly at all for any of it)...something I want to get 
back to, but right now, just another of my "back burner" projects...
Andrew L. Ayers
Glendale, Arizona
phoenixgarage.org
github.com/andrew-ayers