Would have been possible to have an 800XL with slightly better graphics?

[+Philsan]

Technically speaking, when Atari released 800XL in 1983, would have been possible to make it slightly better, in particular on the graphics side, with just new GTIA/ANTIC chips or other little changes?

For example, 4 colors 320x192, 8 colors 160x192, more players/missiles?

[Rybags]

More PMGs - yes.

 

More colour at 320x - that mode uses the full bandwidth of available DMA, so some sort of colour RAM scheme would have been needed.

 

Worst case DMA is 96 for text/charmap + 3 Display List + 1 refresh + 5 PMG = 105.

 

Leaves 9 cycles, of which some could have been devoted to extra PMGs (or even digital sound).

 

They had the golden opportunity to upgrade the base capability, but I suppose compatability would have suffered even more.

 

Plus of course, they spent next to nothing developing or promoting the 8-bit computer line in the 1980s - the XL line was probably more a case of redesign to cut costs rather than properly competing with the C-64 by one-upmanship.

[+bob1200xl]

16 colors in 160x192 would be easier to implement, I think.

 

Sure, they could have just allowed ANTIC to span more memory and/or added a second ANTIC (with its own memory). Implemented an 80 column mode. It all just takes faster clocks and more RAM, both of which became much cheaper with time.

 

Bob

 

 

Technically speaking, when Atari released 800XL in 1983, would have been possible to make it slightly better, in particular on the graphics side, with just new GTIA/ANTIC chips or other little changes?

For example, 4 colors 320x192, 8 colors 160x192, more players/missiles?

[peteym5]

If Atari or someone wanted to make an enhaced ANTIC/GTIA, they probably would have consolidated the 2 chips to one like the proposed CTIA. These chips operated at 2x the CPU and BUS clock speed. If you wanted higher resolution, they probably would have designed it to run at 4x. I have thought about this and discussed the "What Ifs" here before. It is very easy to maintain full backward compatibility with the prior graphics modes. My ideal was to simply use one of the unused registers in the Antic Registers Memory area to go to standard or double resolution modes. For extra Player/Missile graphics, use the memory locations immediately beyond the first GTIA area ($D000 to $D01F) which according to "Mapping the Atari" are just repeats of the first 32 bytes. It would use like ($D000 to $D02F). I feel this is the best way of avoiding compatibility problems. The enhanced chips would need more address lines, maybe 6bits instead of 4 to address the registers.

[emkay]

Technical facts:

 

Around 396 Bytes of the PM graphics are wasted

Gr. 10 uses only 9 of 16 possible colours

Every coloured "Antic" mode uses only 8 of 16 colours by a missing control bit of GTIA

The hires "saturation only" is an intentional "feature" just remove it and have 128 colour in the hires mode with colourclock steps.

The A8 has several graphicsmodes that are not needed. Exchanging them with some hires modes for GTIA-mode speedup would have cost "nothing"

 

 

Conclusion: In the 70s the A8 was a high technical achieved piece of hardware....

But: Until the XL/XE series arrived, only some "low cost clean up" of the chipsets would have done miracles...

 

Doing only some "bugfixing" on the existing chipset would have result not only in "slightly" better graphics.

The potential was high...

[Fröhn]

Technically speaking, when Atari released 800XL in 1983, would have been possible to make it slightly better, in particular on the graphics side, with just new GTIA/ANTIC chips or other little changes?

For example, 4 colors 320x192, 8 colors 160x192, more players/missiles?

First, that isn't "slightly" better, that's "much" better.

 

And yes, you are asking for far too much. You are basically asking for having twice the memory speed + usage (320x192x4 = 30 k = 50% of 800XL RAM) which basically means: More expensive DRAM, total change of the entire bus system including all participants like ANTIC, GTIA and CPU. Most of the 400/800 compability would have been gone too.

 

It would be a completely new design, and definitely nothing which would come out for a homecomputer price in the year 1982/1983.

 

 

The A8 has several graphicsmodes that are not needed. Exchanging them with some hires modes for GTIA-mode speedup would have cost "nothing"

In 1979 many of the low resolution modes were needed because of very limited RAM (8k/16k...). In 1983, those modes are still needed because of compability.

Edited February 27, 2008 by Fröhn

[Rybags]

I wasn't quite right in saying hires uses all bandwidth - the 40-col text modes do but not the bitmap ones.

 

So, something like 320h, 4 colours would have been perfectly feasible.

 

160h in 16 colours, 80h in 256 colours.

 

Although you'd then need an 8 or 9 bit path from Antic->GTIA rather than a 3 bit path.

 

Then again, with 1983 tech, both chips could have been combined into one anyway, including enhancements.

[emkay]

The A8 has several graphicsmodes that are not needed. Exchanging them with some hires modes for GTIA-mode speedup would have cost "nothing"

In 1979 many of the low resolution modes were needed because of very limited RAM (8k/16k...). In 1983, those modes are still needed because of compability.

 

Since they did a rework of the OS, I don't see where the problem is, to set an external bit that tells GTIA to keep hires on, if GTIA modes are overlayed. It worked fine with gr.8 / 15 already.

The hardware "patch" probably was less than a revision update.

[emkay]

Although you'd then need an 8 or 9 bit path from Antic->GTIA rather than a 3 bit path.

 

Why? at the same path that is used for switching the charmode content, the byte for the colours could be set.

That means, something like a 256(128) colour mode for all resolutions for displaying images only, could have been there. without changing the layout and with a 32 bytes width, the computer doesn't stand too busy.

In hires we also could have a 2 byte mode that gives 4 colours to every pixel. But, caused by the colour clock limitations it would do better to have 16 colours for every 2 pixel.

 

All in theory

[Rybags]

Antic only passes 3 bits to GTIA per machine cycle - which is a limiting factor if thinking of raising number of colours available in existing modes.

[MaPa]

And yes, you are asking for far too much. You are basically asking for having twice the memory speed + usage (320x192x4 = 30 k = 50% of 800XL RAM) which basically means: More expensive DRAM, total change of the entire bus system including all participants like ANTIC, GTIA and CPU. Most of the 400/800 compability would have been gone too.

 

320x192x4colors would take "only" 16k not 30k as you wrote (misstake I suppose).

[peteym5]

Well I made a prior statement about doubling the internal color clock speed of a single Antic/GTIA compatible chip (7mhz). I am not totally sure about how this effects the main bus when a video chip takes control for displaying. Probably would not have been hard to have a ways of taking up less bandwidth/bus cycles. The NES video & Maria chip ran internally at 7+mhz and left time for the main cpu. With the modes people mention about it consuming 16k of ram (320x4 or 160x16), the FREDDIE chip would have solve the problem with having an option of using extended memory.

 

I did mention several ways of maintaining software compatibility with the prior Antic/GTIA but seem to have been ignored. Both memory areas had spare bytes available for extra registers. If a chip was available that starting using them, it would still run everything because the old software did not read/write to these areas anyway.

 

Correcting the bugs would have helped. Having all 16 luminescences available for the Antic modes would be a good start.

 

Have to keep in mind the reasons why Atari kept using the Antic/GTIA was that it was cheaper for them. They stockpiled thousands of these chips already and it has cheaper using existing stuff. Even after Jack Tramiel took over, they still had thousands left, and why he created the 130XE and XEGS. These chips are still around today. The original chip designers left due to management at Atari.

Edited February 28, 2008 by peteym5

[analmux]

...The NES video & Maria chip ran internally at 7+mhz and left time for the main cpu...

 

I'm sorry to differ with you, but the NES video chip operates on a separate bus. There's only an indirect transfer between the two busses, but there's no possibility to access video RAM from CPU at time the videochip uses it. So, transfers, by using a memory window, are only possible in the VBLANK period.

[+CharlieChaplin]

And err well,

guess why second Antic, GTIA, Pokey etc. are possible ? Old Atari once planned this as updates or upgrades with later machines, alas it never happened. But there are some protos like Kerri/Kerry (Antic + GTIA in one chip) available... guess there were also tries with two Antics and two GTIAs in one machine and also with one Antic and two GTIAs in one machine... there also was a proto available that had two pokeys in one chip and afaik even a proto that had four pokeys in one chip...

 

In 1982-1984 Atari engineers and developers had quite many ideas and protos - but none of them made it into regular production... -Andreas Koch.

[kenfused]

And err well,

guess why second Antic, GTIA, Pokey etc. are possible ? Old Atari once planned this as updates or upgrades with later machines, alas it never happened. But there are some protos like Kerri/Kerry (Antic + GTIA in one chip) available... guess there were also tries with two Antics and two GTIAs in one machine and also with one Antic and two GTIAs in one machine... there also was a proto available that had two pokeys in one chip and afaik even a proto that had four pokeys in one chip...

 

In 1982-1984 Atari engineers and developers had quite many ideas and protos - but none of them made it into regular production... -Andreas Koch.

I think quad pokey is more than a prototype. I am pretty sure they used them on a couple of their arcade machines. I think there is even an adapter available somewhere to plug 4 pokeys into to replace it since they are rather scarce when a replacement is needed.