External Maria Chip?

[Ecernosoft]

Hello!

I was wondering if it would be possible to add an extra maria chip into the cart to provide video, (Possibly be overclocked and slightly modded to have more sprites per line/full screen 320B/C and the stuff or more colors in 320 modes) to get around DMA. The halt line could be connected to MSTAT instead of MSTAT being for when "VBLANK" occours.

 

Just asking.

[+x=usr(1536)]

35 minutes ago, Ecernosoft said:

I was wondering if it would be possible to add an extra maria chip into the cart to provide video, (Possibly be overclocked and slightly modded to have more sprites per line/full screen 320B/C and the stuff or more colors in 320 modes) to get around DMA. The halt line could be connected to MSTAT instead of MSTAT being for when "VBLANK" occours.

As there's no video input line on the 7800's cartridge port, how do you envisage the on-cart MARIA outputting any video it might generate?

[+Muddyfunster]

23 minutes ago, x=usr(1536) said:

As there's no video input line on the 7800's cartridge port, how do you envisage the on-cart MARIA outputting any video it might generate?

I can't speak to an on cart Maria or any shenanigans like that but I think the upcoming GD7800 has RGB out via the cart. I saw the cart shells on a Twitter update a while back and it mentioned an AV port and the pictures show games running with video out via the cart (looks like a megadrive RGB cable in one pic)

 

I'm not a hardware guy so maybe I'm completely misunderstanding something.

 

[edit] Here's the link.

 

[edit2] updated link

[+x=usr(1536)]

2 hours ago, Muddyfunster said:

I can't speak to an on cart Maria or any shenanigans like that but I think the upcoming GD7800 has RGB out via the cart. I saw the cart shells on a Twitter update a while back and it mentioned an AV port and the pictures show games running with video out via the cart (looks like a megadrive RGB cable in one pic)

Interesting.  I knew this was in the works, but had figured that the featureset would be more akin to the Jaguar / Lynx GameDrive cartridges.

2 hours ago, Muddyfunster said:

I'm not a hardware guy so maybe I'm completely misunderstanding something.

And I have no special insight here, but one of their tweets is interesting:

 

 

I'm wondering how much heavy lifting the RISC-V is doing.  It would certainly have enough horsepower to emulate MARIA, so could potentially run that in parallel to the MARIA in hardware on the 7800.  That would give a way to handle video generation and output independently, making an on-cart RGB output a realistic proposition.

 

This is possibly how they're also handling the dual-POKEY and YM2151 sound, come to think of it.  Or I'm completely wrong

[Ecernosoft]

14 minutes ago, x=usr(1536) said:

Interesting.  I knew this was in the works, but had figured that the featureset would be more akin to the Jaguar / Lynx GameDrive cartridges.

And I have no special insight here, but one of their tweets is interesting:

 

 

I'm wondering how much heavy lifting the RISC-V is doing.  It would certainly have enough horsepower to emulate MARIA, so could potentially run that in parallel to the MARIA in hardware on the 7800.  That would give a way to handle video generation and output independently, making an on-cart RGB output a realistic proposition.

 

This is possibly how they're also handling the dual-POKEY and YM2151 sound, come to think of it.  Or I'm completely wrong

That's true, but seeing as the ARM is more powerful than the 7800 itself, I think it is a bit cheating. An on-board maria (Running at twice the clock speed and hence, twice the cycle count per scanline would require modifications) sounds more worth it if we want to stay ethical, or an FPGA.

[+x=usr(1536)]

20 minutes ago, Ecernosoft said:

That's true, but seeing as the ARM is more powerful than the 7800 itself, I think it is a bit cheating.

Yeah, I can kinda go both ways on this.  Your point does have merit, though.

 

Where I'm stuck is that if an on-cart MARIA emulation doesn't disable, bypass, or interfere with the operation of the one in the 7800 itself, then the only thing it really touches is RGB output - and since the machine never had that to begin with (along with the cartridge and its CPU), it's not doing any harm.  It's not giving a completely original experience of the hardware, but there's a good argument to be made that installing a UAV doesn't either.

 

It's a tricky one.  While I'm far from being against hardware modifications and emulation in general, this could well be a hybrid approach.  Admittedly, all of the above is speculation, so until we get more details from RetroHQ as to how the GD7800 operates it's all a moot point.

20 minutes ago, Ecernosoft said:

An on-board maria (Running at twice the clock speed and hence, twice the cycle count per scanline would require modifications) sounds more worth it if we want to stay ethical, or an FPGA.

Are you referring to a second on-board MARIA or bumping the speed of the existing one?  I'm not totally clear on that, but either one brings up some interesting questions.

[Ecernosoft]

2 minutes ago, x=usr(1536) said:

Yeah, I can kinda go both ways on this.  Your point does have merit, though.

 

Where I'm stuck is that if an on-cart MARIA emulation doesn't disable, bypass, or interfere with the operation of the one in the 7800 itself, then the only thing it really touches is RGB output - and since the machine never had that to begin with (along with the cartridge and its CPU), it's not doing any harm.  It's not giving a completely original experience of the hardware, but there's a good argument to be made that installing a UAV doesn't either.

 

It's a tricky one.  While I'm far from being against hardware modifications and emulation in general, this could well be a hybrid approach.  Admittedly, all of the above is speculation, so until we get more details from RetroHQ as to how the GD7800 operates it's all a moot point.

Are you referring to a second on-board MARIA or bumping the speed of the existing one?  I'm not totally clear on that, but either one brings up some interesting questions.

Disable DMA on on-board MARIA???? Set on-board MARIA CTRL to %01100000 ????

[+x=usr(1536)]

8 minutes ago, Ecernosoft said:

Disable DMA on on-board MARIA???? Set on-board MARIA CTRL to %01100000 ????

Yep.  Your guess is as good as mine (or anyone else's for that matter).

 

Given that the cartridge is loading the ROM via the RISC-V, the RISC-V would have access to the entire memory region in use by MARIA.  Intercepting calls to or from MARIA-specific memory locations and passing them to the on-cart MARIA implementation as well as the console hardware wouldn't be out of the question by any means.  That, in turn, would open up a path for RGB output.

 

In any event, I ended up asking SainT over in this thread about how it's being accomplished, so, in the interests of not spreading speculation and / or misinformation, I'm looking forward to hearing what he has to say.

[Ecernosoft]

6 minutes ago, x=usr(1536) said:

Yep.  Your guess is as good as mine (or anyone else's for that matter).

 

Given that the cartridge is loading the ROM via the RISC-V, the RISC-V would have access to the entire memory region in use by MARIA.  Intercepting calls to or from MARIA-specific memory locations and passing them to the on-cart MARIA implementation as well as the console hardware wouldn't be out of the question by any means.  That, in turn, would open up a path for RGB output.

 

In any event, I ended up asking SainT over in this thread about how it's being accomplished, so, in the interests of not spreading speculation and / or misinformation, I'm looking forward to hearing what he has to say.

You could use 16 or 32K of RAM and have address 12 unconnected (And then move 13 to 12, 14 to 13, and 15 to 14 for 15 data lines (bit 0 = line 0)  so that the HOLEY DMA could be activated while not having issues with the RAM. 16K is cheaper, but with 32K you get extra space for tilemaps, DL and DLL stuff, as well as more graphics storage if needed.

Edited September 29, 2022 by Ecernosoft

[SainT]

There is no software emulation, that would be insane. 😆 The RISCV softcore on the cart is very much for house-keeping, reading memory cards, reacting to input, that kind of thing. It's only clocked at a low speed, so the processing capabilities are limited compared to something like a dedicated ARM core.

 

It's the same approach Krikzz is using in his latest RGBBlaster for the NES. I have to admit, the inspiration did come from him.

 

I have re-created Maria (at a hardware level) on the cartridge and it runs in parallel with the Maria on the 7800. So the RGB output is entirely separate from the 7800 and the "real" Maria. This second Maria implementation is entirely firmware-updatable, so if any problems are discovered (I'm sure there will be some) then I can patch them.

 

Oh, and just for reference, the POKEY, TIA and YM are also proper hardware level implementations, no software involved. It is using the same audio cores as MiSTer uses for the 7800, I have arrangements in place or to be finalised (when the cart is released) with the authors to use these existing cores.

Edited September 29, 2022 by SainT

[Ecernosoft]

2 hours ago, SainT said:

There is no software emulation, that would be insane. 😆 The RISCV softcore on the cart is very much for house-keeping, reading memory cards, reacting to input, that kind of thing. It's only clocked at a low speed, so the processing capabilities are limited compared to something like a dedicated ARM core.

 

It's the same approach Krikzz is using in his latest RGBBlaster for the NES. I have to admit, the inspiration did come from him.

 

I have re-created Maria (at a hardware level) on the cartridge and it runs in parallel with the Maria on the 7800. So the RGB output is entirely separate from the 7800 and the "real" Maria. This second Maria implementation is entirely firmware-updatable, so if any problems are discovered (I'm sure there will be some) then I can patch them.

 

Oh, and just for reference, the POKEY, TIA and YM are also proper hardware level implementations, no software involved. It is using the same audio cores as MiSTer uses for the 7800, I have arrangements in place or to be finalised (when the cart is released) with the authors to use these existing cores.

*Atari 2600 emulating Magnavox oddesy*