DMA Problem with ROMBoards

[Bryce]

Hi all,
     while experimenting with some hardware here, I encountered a strange/interesting issue with the CPC6128+. If I connect a MegaFlash to the Plus and then try to run something that uses DMA Sound, the CPC freezes. I've connected other ROMBoards and they do exactly the same, so it's not a dodgy MegaFlash. I also didn't have ROMs 0 or 7 enabled on the MegaFlash. I can see no hardware reason for this, unless it's a bug in the ASIC. Does anyone else have a Plus and a ROMBoard to test this? Is it just my Plus, or is it a design bug?

Bryce.

[andycadley]

Curious. I haven't got a ROMboard to test it with, but it seems odd that only DMA sound would cause it. Are you trying any particular software out? Does plus stuff which doesn't use DMA sound all work fine?

[Bryce]

I'm running the Diagnostic Cartridge. Everything including Sprites, 4096 Colours etc work fine. If a ROMBoard is plugged in the DMA Sound test freezes just before it should start playing music. This even happens if the ROMBoard has no ROMs installed. If I remove the ROMBoard the test runs as it should. The plus has no further mods or expansions connected at the time.

Bryce.

[andycadley]

Does it crash if you try Burnin' Rubber? That uses the DMA for the tyre screech effect, so if it crashes then it probably rules out something like the diagnostics cart just doing something odd, like paging a ROM that wasn't expected or something.
I would have thought someone would have tried a ROMboard on a plus at some point in the past and I don't recall having ever heard of the issue before. I suppose it's not beyond the bounds of possibility that the DMA is putting values on the bus that might upset external hardware though.

[TFM]

Hi all,
     while experimenting with some hardware here, I encountered a strange/interesting issue with the CPC6128+. If I connect a MegaFlash to the Plus and then try to run something that uses DMA Sound, the CPC freezes. I've connected other ROMBoards and they do exactly the same, so it's not a dodgy MegaFlash. I also didn't have ROMs 0 or 7 enabled on the MegaFlash. I can see no hardware reason for this, unless it's a bug in the ASIC. Does anyone else have a Plus and a ROMBoard to test this? Is it just my Plus, or is it a design bug?

Bryce.

Well, I did run the Cadjo Clan DMA sound demo more often (it extensively uses DMA sound) and I always had connected a ROM-ROM-Box or an Eprom Card, or SF2. I never had problems. Maybe it's your Plus, but more comments on this topic would be beneficial.

[beaker]

Does it crash if you try Burnin' Rubber? That uses the DMA for the tyre screech effect, so if it crashes then it probably rules out something like the diagnostics cart just doing something odd, like paging a ROM that wasn't expected or something.

I just had a quick 10 minute blast on Burnin' Rubber on my 6128+ with the Megaflash plugged in and it was fine...

[Bryce]

So did I, so it's not the DMA sound, but something the Diagnostic Cartridge is doing. Unfortunately, FOS doea exactly the same freeze on mine. Can you install and start FOS on your MegaFlash and see if it crashes or your Plus?

Bryce.

[TFM]

Can you install and start FOS on your MegaFlash and see if it crashes or your Plus?

Bryce.

All 6128 Plus and MegaFlash owners are called for help! 


FutureOS Plus does:

- Unlock the ASIC
- Write 256 byte to first hardware sprite
- Change X, Y coordinates of the first hardware sprite according to input devices
- Checks the analogue port constantly (for mouse arrow movement)
- (Therefore the Memory mapped page gets activated / deactivated)

That's all what it does IIRC. Shouldn't be a problem


Differences to Cadjo Clan demo: Mainly the check of the analogue joystick port

[Executioner]

It sounds to me like it may be a conflict with the secondary ROM mapping register, although I can't see why FOS would be using that. Does Frogger work with the ROM board?

[Bryce]

Haven't checked frogger yet.

@TFM: The strange bit is, it's not just the Plus Version of FOS that crashes the Plus, the standard version does the same.

Bryce.

[Ygdrazil]

@Bryce

you sure move around! 

Haven't checked frogger yet.

@TFM: The strange bit is, it's not just the Plus Version of FOS that crashes the Plus, the standard version does the same.

Bryce.

[beaker]

Just tried Frogger with the Megaflash plugged in and seems fine for me. If I get time tonight I'll try to put FOS on the megaflash and give it a go if my simple brain can work out how to do it - I've only just put the HxC as b drive and haven't added anything to the megaflash yet - how lazy am I? 

[Bryce]

I'm beginning to think that it has something to do with keyboard scanning. The diagnostic Cartridge also starts scanning the keyboard at exactly the same time as it starts the DMA music.

Bryce.

[arnoldemu]

I'm beginning to think that it has something to do with keyboard scanning. The diagnostic Cartridge also starts scanning the keyboard at exactly the same time as it starts the DMA music.

Bryce.

it may be a bug in the cartridge.

the test cartridge activates rom 1 in the range &c000-&ffff. I think it means to access &81 to ensure it gets the cartridge page.
this part of the cartridge is meant to contain sound data I think which is copied to ram and played.

the rom in the expansion board takes priority, it then tries to play it.. perhaps it then ends up with an interrupt which is never acknowledged and it locks up.

[Bryce]

Arnoldemu, I tip my my hat in recognition in your general direction. That's the first decent explaination I've heard, why it might not work. Now I need to find out whether this is or a similar bug is why FOS doesn't run, or whether it's something completely different.

Bryce.

[TFM]

Haven't checked frogger yet.

@TFM: The strange bit is, it's not just the Plus Version of FOS that crashes the Plus, the standard version does the same.

Bryce.

It uses RAM configuration &7FC3 (a bit unusual), so it's RAM mapping... This comes close to that what the Executioner said. Maybe... something connected to banking. You can play a bit with OUT commands...

If I get time tonight I'll try to put FOS on the megaflash and give it a go if my simple brain can work out how to do it - I've only just put the HxC as b drive ...

Ok, just move the mouse arrow over the letters, click, then click at the DIR icon. Click at a filename and then the RUN icon (but the filename should be a FutureOS program).

Short description here: http://www.colorado-boys-muenchen.de/users/futureos/files/FutureOS_Manual.doc

Some more information here: http://www.colorado-boys-muenchen.de/users/futureos/files/FutureOS%20Handbook.docx

the rom in the expansion board takes priority, it then tries to play it.. perhaps it then ends up with an interrupt which is never acknowledged and it locks up.

Well, wouldn't in this case all ROMs cause troubles?

[Bryce]

Do both Versions of FOS (Plus and standard) do this?

Bryce.

[TFM]

Do both Versions of FOS (Plus and standard) do this?

Bryce.

Yes, both use RAM config &C3, and also CP/M Plus does it. Just start CP/M Plus and check if it runs, also give SOS a try, it also uses &C3.

[Bryce]

SOS was my next on the list to try I want to try all the previous things on a classic CPC first (other than diagnostics), to rule out any problems with the MegaFlash and the FOS installation, then I will try out SOS (after testing your Init routine of course! )

Bryce.

[TFM]

Thanks' Bryce! Even in the darkest hours you still think about other people first! You'll be always a hero of the CPC scene 

[Bryce]

It's not dark yet, it's only 4:10 here

Bryce.

[arnoldemu]

Well, wouldn't in this case all ROMs cause troubles?

All expansion roms in slot 1 could cause trouble when running the plus diagnostic cart and running the dma sound test, because the rom on the expansion board takes priority over cartridge roms *when* you choose them like a normal rom:

e.g.
ld bc,&df01
out (c),c

compared to the correct way:
ld bc,&df81
out (c),c

which should not cause problems and specifically chooses bank 1 of the cartridge rom.. but then also depends on how the expansion board decodes the rom select bits. (does it only decode lower 4 bits... and then the effect is the same.. or...)

and it also depends on what data they in them at the location the diagnostic cart wants to read.

the lockup sounds like it could be an interrupt that is never acknowledged.. but I don't know without simulating it.

As for the c3 problem, this is likely to be different?

[Bryce]

Unlike cheaper ROMBoards from the 80's/90's the MegaFlash does decode all 8 bits from D0 to D7, does this mean it shouldn't have this issue?

Bryce.

[andycadley]

It means it should be fine if the cartridge software is doing what it's supposed to, but might go wrong if the cartridge software is trying to page it's ROMs using ROM numbers  < 15 (but there really isn't anything you could do about that)

[beaker]

So did I, so it's not the DMA sound, but something the Diagnostic Cartridge is doing. Unfortunately, FOS doea exactly the same freeze on mine. Can you install and start FOS on your MegaFlash and see if it crashes or your Plus?

Bryce.

Thanks TFM for the document links.

OK, I want to check I am not being stupid as mine also crashed as well as soon as I loaded the desktop. Let me know if there's a better way of doing this as I am guessing all the way here. I downloaded FutureOS_System_.8_Preview!!!.zip from FutureOS - The revolutionary UltraOS for the CPC6128 and CPCPlus and extracted 180 FutureOS-ROMs .8 English 2011-10-10.dsk which I opened in the HxC floppy emulator software and exported to a .hfe file. I then used disckit3 in cpm to copy the image from the HxC to a real floppy in drive a. First I tried to use the rom manger from basic (-rma) to copy the rom images myself but that didn't really work when I typed |fdesk so I ran the disc.bas and chose option 7 even though it was meant for the original 6128. This put the roms in the following positions:

[attach=2]

When I boot up the CPC I get this:

[attach=3]

When I run |fdesk I get the following screen but the CPC appears frozen. The pointer won't move using either the cursor keys nor the using the direction buttons on the pad.

[attach=4]

Was this what you were expecting Bryce? Sorry I can't be more help; I am not hugely knowledgable about the CPC having only really used the 464 as a games machine as a kid...