"what-if" QL extended graphics

[M68008]

Am I right to assume that if you were to add more memory and a FPGA there would even more colors be possible ein Mode 4 and 8 and that this would rather be a 'graphics card' instead of a replacement board?

Yes, and as an aside (I don't mean to hijack this thread) I started writing something like that (QL graphics card) for fun some time ago. I have some FPGA code running on Mister and using the QL screen format, palettes, 15 sprites, hardware scrolling and more. Very far from finished, especially as I wanted to add even more features and still doing some historical research when I have time.

Cool stuff. Sounds very tempting. Would this meant to be plugged into the expansion port (normally occupied by Gold Cards etc.) or be an internal version?

Hi thorsinclair, now that I re-read your comment, what I was experimenting with doesn't look like what you describe because I don't have extra video memory. The palette allows to assign each of the 4 or 16 pixel values to one of 4096 possible colours, though.

Two ways one could interface such a thing to a real QL, each with pros and cons: either as an expansion card or as a ZX8301 replacement. In my case, I chose the second one, since more than anything else it is a thought experiment about how the QL might have looked in the 80s if Sinclair wanted to provide it with some multimedia and gaming capabilities from the start. I think the rest of the design for such a machine could still have looked exactly like the QL, except that it would have needed the full 16 bit 68000, faster RAM, and perhaps more responsive 8049 firmware. (Also better sound of course, but that's outside the scope of my experiment.)

[thorsinclair]

Hi Daniele,

thanks for this. I like the "what-if" approach to to build up on the existing and make it better by keeping compatibility. Very interesting, please keep us posted, thanks.

Best
Thorsten

[Nasta]

Here's a little hint that might be useful:
The QL memory map has an informal unassigned area of 16k right 'under' the bottom of the screen 0 RAM.
Originally the on-board IO for the QL has been documented as residing in a 64k block of addresses starting at $10000, however, if one looks at what addresses are actually used, it is actually in a 16k block at $18000 to $1BFFFF, In actuality it is sparsely used and could even be more confined but let's use this for simplicity's sake.
Minerva in particular made this 'canon' by looking for additional ROM or IO boards at $10000 and $14000.
This leaves the 16k block at $1C000..$1FFFF free, on a regular QL (no GC or SGC).
Since the regular SCR0 screen starts right at $20000 and extends up by 32k to $17FFF, concatenating these two areas assuming appropriate hardware, makes it possible to have 48k of screen RAM without having to move the system variables, which is required for instance to use SCR1 with Minerva, but rather moving the screen start address to $1C000.
Up to 48k can then be used to extend the resolution in existing modes 4 and 8, or add new modes.
One interesting one could be 256x192 in 256 colors...
Such hardware would most probably require it's own fast RAM which it would map itself instead of the on-board QL RAM so the required decoding and speed can be achieved, and would likely be an add-on board, although something like a 8301 replacement could be made, that would simply render the QL motherboard RAM inert, and use it's own.

[Derek_Stewart]

Hi,

Could SCR0 & SCR1 be combined, so that there 512x512 available.

Sort like the Second Screen enabled, but all the video accessible.

This would mean moving the System Variables, which is already done with Minerva

[M68008]

Thank you Derek and Nasta, those are interesting suggestions to increase graphics capabilities!

When it comes to games, 256x256x16 plus extra colors for sprites is probably relatively good (for the 80s) despite the odd aspect ratio. Arcades like Pacman had a resolution of 224x288.

[Cristian]

As an example: Double Dragon 2 (1989)
"only" 240x224 (plus more colors, obviouvsly)

[ones' complement]

When it comes to games, 256x256x16 plus extra colors for sprites is probably relatively good (for the 80s) despite the odd aspect ratio. Arcades like Pacman had a resolution of 224x288.

To 'cut to the quick' (no disrespect) the V9958 off the QL ROMport would fit the bill exactly!

[M68008]

To 'cut to the quick' (no disrespect) the V9958 off the QL ROMport would fit the bill exactly!

Come on, where's the fun in that?

But thanks! I will take a look at the manual in case there's any interesting ideas.

Probably 100 people wanting to enhance the QL graphics abilities would come up with 100 very different designs, all valid.
I'm trying to add to the existing QL video design without disrupting or replacing it, so same pixel format and no additional VRAM (except if needed in practice for speed reasons). Also to learn a bit more about FPGA and how video coprocessor hardware worked in the early 80s.

[Pr0f]

The only down side of the Yamaha VDP's is that they are accessed over an I/O port to update their own separate VRAMS with your display data. Whilst they do offer some forms of DMA operation - this won't be easy to setup on the QL side. A bitmapped display is probably a better way to increase the resolution or colour depth - as per the Aurora or Q68 - but the downside is having to find room for that memory in the memory map, and also that the QL's graphic and text routines are all coded for the default display - so you'd need to alter some of these for sure.

[ones' complement]

Yes, only port access, but quick and easy to realise.

BTW in case you missed it, interesting 68K system using V9958 currently being developed: Y Ddraig