Banked Video RAM?

[McArti0]

The latter is my biggest concern. Even if someone would be willing to add the logic, it would not work on anything else but an unexpanded 6128. As soon as you have a different machine or a RAM expansion you end up with the original logic where the GateArray cannot access anything but the primary 64KB.

I don't understand why the whole Amiga world is playing mods and extensions and kickstarts and systems for non-existent Amiga without Motorola processors and why CPC can't have a mod for 128 kB of its own vRam. People, have fun! Eto do you know what are the resistors R155 and R156 in CPC+? We need to put jumpers there and add 128kB vRam mod as well. :-D

This is BIG mistake CPC design flaw.

[norecess464]

why CPC can't have a mod for 128 kB of its own vRam

Well, in the end maybe what you want is something else than an Amstrad machine?

I'm not sure that more VRAM would really put something new on the table. Especially since it's still pretty rare nowadays to see the 64Kb of VRAM fully used.

Keep in mind that 10 years ago, @SyX and @TotO created an expansion that expanded the machine with real new hardware features, the PlayCity (https://www.cpcwiki.eu/index.php?title=PlayCity&mobileaction=toggle_view_desktop). But, this did not bring much traction.

[McArti0]

I don't think PlayCity is a small cheap enabler of existing possibilities. Something like add one resistor between sound and motor wire and/or write data and add fifth PWM channel.

[HAL6128]

Interesting discussion. But from a electrician noob view the proposed adapter just sounds like another way of a memory expansion?
(I'm sure that I'm completely wrong )

[McArti0]

For noob. Now on screen we can show 16kB bank 1 and 3 (very very rarely 0 and 2). After MOD we can very easy show on screen all 16kb banks 0,1,2,3,4,5,6,7.
Usable 6 screens banks 1,3,4,5,6,7.

[andycadley]

I don't know whether that would work on a Plus, but it'd be deeply cumbersome. Unlike the original models, where it only affects the screen, on a Plus changing the banking would affect both visible screens and also where DMA lists were fetched from. It would be hard to use that sort of arrangement in a meaningful way without causing glitches (and honestly running from cart you have the better part of 64K CRTC accessible RAM available for whatever you want to do regardless).

[eto]

Eto do you know what are the resistors R155 and R156 in CPC+?

Yes. And you would have to do quite some soldering to get access to D6,D7,IORQ,WR, A15,A14 and CPU/Wait.

Don't get me wrong, I like the idea and it would definitely be worth to see what benefit it has in a normal, unexpanded CPC 6128. It will just be hard to make it work for anything else but a standard 6128.

[HAL6128]

For noob. Now on screen we can show 16kB bank 1 and 3 (very very rarely 0 and 2). After MOD we can very easy show on screen all 16kb banks 0,1,2,3,4,5,6,7.
Usable 6 screens banks 1,3,4,5,6,7.

Ok, understand. It means that the CPC is able to flip fast between the whole spectrum of banks inside a 6128, right?
It's an advantage working with Overscreen / Fullscreen and double buffering?

[McArti0]

Yes. Yes. How easy it will be to draw even in basic on all 6 screens and make animations with ease.

For me, must have.

[McArti0]

Eto do you know what are the resistors R155 and R156 in CPC+?

Yes. And you would have to do quite some soldering to get access to D6,D7,IORQ,WR, A15,A14 and CPU/Wait.

Don't get me wrong, I like the idea and it would definitely be worth to see what benefit it has in a normal, unexpanded CPC 6128. It will just be hard to make it work for anything else but a standard 6128.

D6,D7,IORQ,WR, A15,A14 from expanded port? Second. This project consists of two parts. Part of multiplexers and part of the trigger. Part of the triger may be different than my proposal.

ps. Well, if someone bought a bad non development computer, what can I do? A joke of course. 

[PulkoMandy]

I don't understand why the whole Amiga world is playing mods and extensions and kickstarts and systems for non-existent Amiga without Motorola processors and why CPC can't have a mod for 128 kB of its own vRam

The Amiga had several machines already in its commercial lifetime with major differences in CPU and other hardware. And also a somewhat higher level OS that allows apps to run on such hardware variations.

The CPC on the other hand is all about having a fixed machine and everyone pretty much running the same hardware. Also, it is not a so greatly designed machine, and if you start making such changes and "fixing" design decisions, quickly enough you end up with a different and slightly incompatible z80 machine. Even Amstrad found this out with the Amstrad Plus range!

That does not prevent from having fun, of course, but, you don't really need to attach the CPC name to what you do. Several years ago there were some projects (CPC-NG and CPCMax!) that did something like this, but did not result in much usable things. Maybe it would be easier today with more modern tools?

[HAL6128]

Would such adapter end up in an incompatible machine?

[McArti0]

you don't really need to attach the CPC name to what you do

This is only Upgrade-feature, its real CPC 1985.

[McArti0]

Would such adapter end up in an incompatible machine?

I think it could be done as an upgrade from 464 to real 6128.
The CPC+ needs more longer wires and soldering because he has not socket. 

[Anthony Flack]

There's always a chicken and egg situation with hardware mods and software. I don't want to do a hardware mod just to run one demo. And I don't want to write software that will only run on one person's CPC.

The Amiga already had loads of existing 3d games that run better with an accelerator, that's the difference. It works with existing software and makes it better.

I want to do something that uses the Plus machine's analogue joystick port sometime, but even that might be limiting myself to an audience of myself.

[McArti0]

I agree. The dissemination process is to create a visually stunning game with great gameplay that requires a 10euro/usd hardware upgrade to run. Then people think I want too.

[zhulien]

Well... I put a 60hz switch in my CPC to run a single demo of bouncing balls that was coded for 60hz for some reason.  Granted the CPC was designed to have 50hz and 60hz.  Not sure if any countries had 60hz CPCs configured that way though upon shipping.

CRTC seeing banked RAM does give a little benefit here and there - I guess if it is backward compatible and easy to do, why not do it?

Then we can have:

- reset button
- multiface 2 button
- 50hz / 60hz switch
- ABBA switch
- 40/80 track switch
- OSROM switch
- hackit switch
- CRTC Banking switch

[eto]

I guess if it is backward compatible and easy to do, why not do it?

I guess it won't be compatible as soon as a RAM expansion is attached. I could imagine that it works with Revaldinhos old-school expansion as the second internal bank could still shadow the contents of the first external bank, but if its an expansion that overrides a signal, the second internal bank will no longer carry the RAM content. And the CRTC/GateArray will never be able to access the expansion RAM. 

[McArti0]

it won't be compatible as soon as a RAM expansion is attached.

Only adapter needed. 

[eto]

Only adapter needed. 

what kind of adapter?

how would you prevent a ram expansion from overriding MREQ (or was it WR?) with an adapter?

[McArti0]

Next register for &7FFF,&Cx and gated all?

[McArti0]

CPC 6320 and CPC 6512. 
Why don't you say that history knows such cases.

ps. zhulien 512K VRAM possible. I'm dying laughing

[eto]

Next register for &7FFF,&Cx and gated all?

I'm not sure if I can follow your thoughts. I might be missing something, but afaik external RAM expansions, at least those that are compatible with the 464, override signals to prevent writes to internal RAM. If such an expansion is connected to the CPC the second RAM bank of the 6128 will no longer receive writes from the CPU. Then it's useless to the GateArray too. 

If I am right, a user would have to remove the expansion before running an application that uses advantage of the extended PAL. Still feasible, just needs to be considered. 

CPC 6320 and CPC 6512. 
Why don't you say that history knows such cases.

Sure, they could be enhanced to support this idea. But they also require to replace a lot of RAM ICs, which only few will consider doing. 

[zhulien]

I guess if it is backward compatible and easy to do, why not do it?

I guess it won't be compatible as soon as a RAM expansion is attached. I could imagine that it works with Revaldinhos old-school expansion as the second internal bank could still shadow the contents of the first external bank, but if its an expansion that overrides a signal, the second internal bank will no longer carry the RAM content. And the CRTC/GateArray will never be able to access the expansion RAM.

The way I would impement it then is a new set of I/O ports with a new RAM expansion for it - if it is worthwhile to do so.

This new RAM expansion of course co-exists with existing, at the moment we have physical RAM chips on the CPC that video RAM is in, separately to the bank switching of conventional memory expansions, why not switch other external RAM with the current physical chips.  This should allow both methods to work together or independently.

[McArti0]

I write about this next adapter a bit jokingly. It sure would be complicated. I imagine it similar to the 256KB Silicon Disk. 128int+256ext.
I haven't considered refreshing the DRAM.