What is the 7800 really capable of?

[Crazyace]

If you set up 12 16 high zones as follows ( using 40 byte wide with 2 sprites to give 160 pixels )

 

$6000

$7000

$6000+40

$7000+40

$6000+80

$7000+80

$6000+120

$7000+120

$6000+160

$7000+160

$6000+200

$7000+200

 

Then calculating address from X,Y is pretty simple..

 

t = Y & 224

address high = (Y &31)| $60

address low = t + (t/4) + (X/4)

 

horizontal spans are consecutive, and vertical go up by 256 in zones - which can be used in line draw routines

 

This works with the standard atari ram cartridge - you also have 2 groups of 16 bytes wide for ram sprites or vars.

[Gorf]

If you set up 12 16 high zones as follows ( using 40 byte wide with 2 sprites to give 160 pixels )

 

$6000

$7000

$6000+40

$7000+40

$6000+80

$7000+80

$6000+120

$7000+120

$6000+160

$7000+160

$6000+200

$7000+200

 

Then calculating address from X,Y is pretty simple..

 

t = Y & 224

address high = (Y &31)| $60

address low = t + (t/4) + (X/4)

 

horizontal spans are consecutive, and vertical go up by 256 in zones - which can be used in line draw routines

 

This works with the standard atari ram cartridge - you also have 2 groups of 16 bytes wide for ram sprites or vars.

 

Ah I got ya. But the only trouble with the Atari Ram cart is you cant have a pokey with it.

[Crazyace]

To match the mapping of the RAM best - you could have a 8k + POKEY card

 

4000-5fff POKEY

6000-7fff 8K ram

8000-bfff Banked rom

c000-ffff Fixed bank rom

 

... That should be trivial to add to Mess/Prosystem emulators... I haven't looked at carts.. Does the CuttleCart support Pokey?

It should be easy, but there are lots of other people here with more H/W design experience

[vdub_bobby]

Oh please. The 2600 REQUIRES you to count cycles and chase the raster beam for every single game no matter how simple.

 

True, but with modern emulation it's really not that hard. Often, rather than trying to count cycles I'll simply throw together a little kernel test and find out what things happen to early or too late, and then see if I can fix them. If there's too much stuff going on, it may be difficult or impossible to tweak the timing of a particular instruction without knocking some other timing out of tolerance. But if there isn't much going on, it's usually pretty easy.

I'm not totally discounting what you're saying, but (a) you have to climb up a very steep learning curve and do lots of cycle counting and coding to get to the point where you can just throw something together and be able to interpret what's happening well enough to see what's going wrong and (b) whatever seems easy to you is definitely NOT easy for almost anyone else (maybe TJ).

 

 

And regarding NES vs. 7800 - the 7800 has a few advantages, but the advantages it does have are, first of all, not as great as they at first seem and, second, pretty narrowly focused.

Edited December 6, 2008 by vdub_bobby

[Gorf]

To match the mapping of the RAM best - you could have a 8k + POKEY card

 

4000-5fff POKEY

6000-7fff 8K ram

8000-bfff Banked rom

c000-ffff Fixed bank rom

 

... That should be trivial to add to Mess/Prosystem emulators... I haven't looked at carts.. Does the CuttleCart support Pokey?

It should be easy, but there are lots of other people here with more H/W design experience

 

I would actually open up the entire 16k from $4000-$7FFF for ram

and let the last 16 bytes map to the pokey registers as well.

 

Then you have a serious bank of ram and can even possibly

pull off double buffering.

 

You know actually....I wonder...since you can bank a ton of banks

of ROM...why not wire one of those banks as a pokey bank instead?

Then you can bank it in when you need to write the registers.

 

This way you dont need any fancy decode to map the POKEY to only

the 16 bytes of ram in needs to cover its register file.

[kenfused]

One other possibility for POKEY + RAM is if you don't need read access to POKEY is just maybe map it where the ROM is and it only gets accessed for Write operations. In theory, you can put POKEY whereever you want and with whatever foot print you want (as long as it doesn't interfere with the system,and preferably not the HSC), it just depends how many address lines you want to decode.

 

--Ken

[krewat]

My $.02 (or even less, my memory is fuzzy about this whole thing):

 

The "pixel pushing power" of the 7800 was very limiting. When I did Impossible Mission, I got the leftovers of another developer who quit the company. He had it to a point where it was "OK". Too many robots on the screen, and it started getting flaky. Sprites would start losing their time "in the limelight" and start to flicker badly. But then, that developer's approach was to line-by-line convert the source code from C64 to 7800. Which worked on other games that weren't too heavy on CPU.

 

The one problem with the Maria was that it stole time from the CPU for memory access. The more sprites, the less CPU available.

 

The Commodore 64 had no such problems, or at least, they were very minimal.

 

Converting a somewhat CPU intensive game like Impossible Mission to the Atari was a test in programming efficiency. What I wound up doing was re-writing from scratch major sections of the code. It worked, on the hairy edge, but it worked.

 

Which leads to the question: Of all the games that are "too much" for the 7800, how much could be gained from rewriting code that was obviously from other architectures, to take full advantage of the 7800's abilities (or shortcomings)???

 

What I mean is, there was plenty of crappy code out there. If someone (Atari) paid the developer enough, they could have most likely EASILY gotten much better games to run on the 7800. But didn't.

 

--

 

I remember the sliding-screen feature helped me a bunch on one of the conversions I did - might have been One On One, come to think of it (looks like I'm going to have to update my signature)

 

--

 

Again, there were situations where the 7800 shone compared to the C64, but there weren't many, sadly. And to take advantage of them, you either had to write the game with the 7800 in mind in the first place, or rewrite previously-written crap (sorry to those who authored that stuff).

Edited December 7, 2008 by krewat

[DracIsBack]

What I mean is, there was plenty of crappy code out there. If someone (Atari) paid the developer enough, they could have most likely EASILY gotten much better games to run on the 7800. But didn't.

 

That is really my gripe with all of these comparisons. Taking aside architectural differences between 7800, NES, Commodore 64, SMS etc, the 7800 really suffered from the fact that there are a lot of 7800 games that looked rushed to market without even the most remote attempt to optimize a game for that system. Both the Commodore 64 and the NES were popular machines where primo developers worked their asses off the get more and more out of them. With the 7800, that was very obviously not the case.

 

Sadly, for every one "SIRIUS" or "ALIEN BRIGADE", there are a bunch of KARATEKA'S out there.

 

Even with the architecture as it was, I'm not convinced the library we got for the 7800 is very reflective of the best of what the system could pull off. That's the result of a combination of marketplace acceptance, Tramiel investment in development and cartridge production, development tools and resources.

Edited December 7, 2008 by DracIsBack

[Zap!]

Enough, someone just make a 7800 SMB 1 and/or Alex Kidd In Miracle World and settle this. Just one level is fine. Who's up to it?

[Gorf]

My $.02 (or even less, my memory is fuzzy about this whole thing):

 

 

How would you go about trying to pull off what I am hoping to do?

Using cart ram as a video buffer like the VIC-20 does for high res,

would you use sprites or would you go with the char map as I have

suggested?

 

Impossible Mission:

 

Since you are here...dont know if you were ever asked this but what

was it in the code that casued you not to be able to finish the game?

Did you ever figure out why? And, am I remembering the right game?

[Gorf]

One other possibility for POKEY + RAM is if you don't need read access to POKEY is just maybe map it where the ROM is and it only gets accessed for Write operations. In theory, you can put POKEY whereever you want and with whatever foot print you want (as long as it doesn't interfere with the system,and preferably not the HSC), it just depends how many address lines you want to decode.

 

--Ken

 

 

 

You would definitely need some serious logic decode but I bet a PAL

or GAL could do it just fine. I think a CPLD/FPGA set up with RAM or

ROM and a hardware emulated pokey might be the most practical.

This way you can put everything on one chip and no extra decode

chips on the cart. I'll have to talk to Tursi about this one.

[Lost Dragon]

Very sorry to dig out ye oldie thread, but after reading various magazines coverage of the 7800 over the years, i'm more confused than ever.

 

Very early issue of Retro Gamer magazine had an interview with the designer of the Graphics Chip of the 7800 if my memory serves (i'd have to dig issue out to be sure) and he said 7800 was more powerful than the NES, but not as capable as the Master System.

 

I then read 'recent' 7800 coverage in Retro Gamer (Minority Report coverage etc) which seemed a little too Pro-7800 and suggested it could hold it's own again'st the Master System, yet i've never seen any 7800 game running the higher resolution mode the MS often seemed to pull off.

 

I looked at C+VG's 2-page feature on the console from years back, reviewer commented that the 15 games he'd seen running did'nt compare that favourably (graphically) with the likes of SMB III, Wonderboy 3 etc and that MARIA did it's best to be as flexiable as possible regarding the trade-off between colour and resolution.

[Lost Dragon]

(Cont) and what sprites lacked in colour, they tried to make up for in colour.

I'd also heard the 7800 was some sprite-shifting monster...

Then i read this comment:

Leonard: Maybe it would have, maybe not. The 7800 was basically a 2600 with some things put into hardware that were done in software on the 2600. It was still quite a limited machine. At this point it is difficult to say for sure.

From this interview:http://classicgaming.gamespy.com/View.php?view=Articles.Detail&id=268

And i'm even more confused than ever.

The recent RG articles seem written by a big 7800 fan, so really lacked a certain degree of 'balance' for my personal tastes, but Atari themselves don't seem to rate the hardware, that much, judging by that interview, but said interview claims Panther came out after Jaguar?

Basically just how did the 7800 match up to the Master System? would bigger carts made a difference? or would it of needed to go the NES route and have enhancement chips for graphics ?.

[Lynxpro]

(Cont) and what sprites lacked in colour, they tried to make up for in colour.

 

I'd also heard the 7800 was some sprite-shifting monster...

 

Then i read this comment:

 

Leonard: Maybe it would have, maybe not. The 7800 was basically a 2600 with some things put into hardware that were done in software on the 2600. It was still quite a limited machine. At this point it is difficult to say for sure.

 

From this interview:http://classicgaming.gamespy.com/View.php?view=Articles.Detail&id=268

 

And i'm even more confused than ever.

 

The recent RG articles seem written by a big 7800 fan, so really lacked a certain degree of 'balance' for my personal tastes, but Atari themselves don't seem to rate the hardware, that much, judging by that interview, but said interview claims Panther came out after Jaguar?

 

Basically just how did the 7800 match up to the Master System? would bigger carts made a difference? or would it of needed to go the NES route and have enhancement chips for graphics ?.

 

Leonard Tramiel has always been dismissive of the 7800. He's the one who's always referred to it as a souped-up 2600. But remember, he's from Atari Corp, not Atari Inc or GCC.

[Trebor]

...i've never seen any 7800 game running the higher resolution mode the MS often seemed to pull off...

Sega Master System resolution = 256x192(224)

 

The majority of 7800 games = 160x240

 

The 7800 also handles resolution = 320x240 - 'usually' with a very limited color palette.

However, with some 'tricks', it handles 320x240 like this:

 

http://www.youtube.com/watch?v=JNU1iJzfPFA

 

Now you've seen a 7800 game running a (even) higher resolution mode that the SMS pulled off.

 

Make no mistake about it though, the SMS (1986) base graphics hardware overall blows NES (1983) and 7800 (1984) base graphics hardware away.

 

If similar cartridge enhancement chip(s), such as the MMC5 (Utilized and needed, for example, under Castlevania III) which added the following to the NES base graphics hardware...

 

-Vertical split screen scrolling

-Made 16,384 different tiles available per screen rather than only 256

-Allowed each individual 8x8-pixel background tile to have its own color assignment (Instead of restricted to one color set per 2x2 tile group)

-A scanline-based IRQ counter

...was provided for the MARIA graphics chip of the 7800, the story would play out vastly differently.

Even something as "simple" as allowing more available colors to the 320x240 mode - providing the same (or/and more) colors/options of 160x240 modes to the 320 modes alone would be huge. If you start throwing in all the other things NES cartridge hardware provided such as more memory, assistance with scrolling, in addition to the raw sprite processing power of the MARIA chip (Which is superior to the SMS and NES)...It would be a graphics animal for sure.

[Lost Dragon]

Huge thanks for the info to both of you.I'm going to have to dig through my back issues of RG and look at previous articles (i do recal Marty G's being one of the most balanced looks at the hardware i'd seen) as i believe they are covering it again next month.

 

Nice to see what 7800 was capable of, resolution wise if 'tricks' were used.

 

What was Leonard Tramiel 's 'Beef' with the 7800? (I know very little about Leonard).

 

So to say the 7800 could 'hold it's own' again'st the MS might be a little too Pro-Atari to really stand up to closer observation?.Perhaps something like it was cabable of being pushed (much?) further, yet due to it's limited 'life' we never got to saw what it was (commercially) capable of?.

 

I'm a big Atari fan (owned 600XL, 800XL, Lynx MK1, MK 2, Jaguar and 520STFM) but as a reader, i like my articles to point out a systems shortcomings as well, as they make for just as good a read.There's never a need to 'gloss over' what went wrong, i feel.

[Trebor]

So to say the 7800 could 'hold it's own' again'st the MS might be a little too Pro-Atari to really stand up to closer observation?

 

If we're just discussing "base" hardware in the majority of situations with no additional cartridge hardware (This is crucial point, for instance, ~90% of the entire NES library requires additional cartridge hardware), the SMS could graphically pull off NES and 7800 games well (sans Robotron) without any additional graphics related cartridge hardware.

 

It has similar tile processing abilities of the NES but with more color capabilities for those tiles. Almost think of the SMS as being similar to a base NES with some features of the MMC5 chip as its base graphics hardware. The SMS could likely pull off Castlevania III without any additional graphics hardware assistance, unlike the NES, and be just as good.

 

The advantage the 7800 has over the SMS (and NES too of course) is it's ability to process a much greater number of raw sprites. It could be argued, that a game (like Bubble Bobble) graphically could be pulled off best on the 7800 when the screen becomes filled with numerous sprites. Not that NES or SMS would (does) do a bad job - just that the 7800 can handle more (with no flickering) with its native graphic hardware.

 

Perhaps something like it was cabable of being pushed (much?) further, yet due to it's limited 'life' we never got to saw what it was (commercially) capable of?

Exactly. Here's an amazing homebrew done within only 144KB. A POKEY chip is included for sound. It contains impressive graphics including parallax scrolling in numerous level rounds without requiring any additional graphics hardware support:

 

http://www.youtube.com/watch?v=x0zXvBwA1fE

 

Seeing a game like this under the 7800, one may conclude that it can 'hold its own' against the SMS.

[Lost Dragon]

Blimey! Seeing that Bentley Bear video running does indeed give me the impression the 7800 was capable of a lot more than what i've seen in terms of commercial releases.Very grateful for you putting that up.

 

Would the issue with the 7800, in terms of commercial support, be that old familar (to myself at least as an ex-A8 and Jaguar owner) in as far as Atari just did'nt have the resources (in terms of programming teams) to compete with teams working on what could be classed 'flagship' Nintendo and Sega titles? and so the system was never pushed as far as it might have been.

Also, i guess Sega and more so Nintendo, had pretty much cream of the commercial development teams signed up making games for NES and MS.

 

 

Also given the budget issues (saving money by not putting the Pokey chip on-board the console, instead opting to put it in specific games), that we were unlikely ever to see big sized games in terms of ram avaiable to developers, let alone extra chips to assist with the graphics handling?.

[Trebor]

Would the issue with the 7800, in terms of commercial support, be that old familar (to myself at least as an ex-A8 and Jaguar owner) in as far as Atari just did'nt have the resources (in terms of programming teams) to compete with teams working on what could be classed 'flagship' Nintendo and Sega titles? and so the system was never pushed as far as it might have been.

Also, i guess Sega and more so Nintendo, had pretty much cream of the commercial development teams signed up making games for NES and MS.

Yes, the above among other reasons - some of which the details are more complex; regardless, the above is indeed a huge factor.

 

 

Also given the budget issues (saving money by not putting the Pokey chip on-board the console, instead opting to put it in specific games), that we were unlikely ever to see big sized games in terms of ram avaiable to developers, let alone extra chips to assist with the graphics handling?.

See this:

 

 

256, 512 & 1024k carts were to be made available to the 7800. The highest we received was 144.

 

Thankful to CPUWIZ, homebrewers will have the opportunity of take advantage of larger carts. People like RevEng have provided additional tools to assist in programming and tapping that potential.

 

True, we cannot make up for the past - Imagine what could have been, utilizing the above Bentley Bear as an example with only 144k, if there was seven times more cartridge memory, or even just double, or three and half times more cartridge memory (All of which the NES did receive, btw).

 

It can be mind-boggling. Couple the above with POKEY or/and other sound chip(s) in addition to full time work, for full time paid employees in well supported teams/groups, having great resources at their disposal, developing 7800 games - To say that the 7800 would have been more than formidable competition with a plethora of amazing games is putting it mildly.

 

Looking forward to more exciting stuff for the future though. There are some amazing people a part of the community, and an awesome amount of potential for the 7800 to be tapped even further.

[DracIsBack]

 

Very early issue of Retro Gamer magazine had an interview with the designer of the Graphics Chip of the 7800 if my memory serves (i'd have to dig issue out to be sure) and he said 7800 was more powerful than the NES, but not as capable as the Master System.

 

You sure you're not remembering Sam Tramiel comparing the Jaguar to the Saturn and the Playstation? I definitely remember that being the gist of it.

 

 

 

I then read 'recent' 7800 coverage in Retro Gamer (Minority Report coverage etc) which seemed a little too Pro-7800 and suggested it could hold it's own again'st the Master System, yet i've never seen any 7800 game running the higher resolution mode the MS often seemed to pull off.

 

Pac Man Plus's 320 games all run at higher resolution. But generally, 7800 games run at the lower 160 resolution modes due to flexibility, CPU time etc.

 

The SMS's real strength is actually its colour palette. It has the number of colours in its palette that the 7800 has, makes them brightly like the NES does and puts more on screen (16 per tile, 16 per sprite) than either.

[DracIsBack]

 

Leonard: Maybe it would have, maybe not. The 7800 was basically a 2600 with some things put into hardware that were done in software on the 2600.

 

the fact that this is even said suggests that Leonard wasn't actually that technically familiar with the 7800. The whole different Graphics Architecture is a pretty gigantic difference between the two.

[Trebor]

It has the number of colours in its palette that the 7800 has, makes them brightly like the NES does and puts more on screen (16 per tile, 16 per sprite) than either.

 

Actually, the SMS has a 64 color palette compared to the 7800's 256 color palette; indeed though, the SMS puts more colors on screen at one time than either the NES or 7800.

[Lost Dragon]

@Drac:Nope, it was def.the 7800 being talked about, i'll have a rummage and get back to you.

@Trebor:I'm a sucker for What If.....type scenarios.

I wondered about the 7800 getting the crumbs of the development team table as being an A8 owner so often i saw conversions that whilst probably would'nt have matched the C64 version (A8 less PMG than C64 had sprites?), could have been a lot better given more time/talent.Things like Arkanoid, Green Beret, Rampage etc.All just seemed to need few things adressed or fixedand would have been much better.

[Lost Dragon]

Found it:Retro Gamer Volume 2, Issue 2 (said it was an early issue, lol).

 

Steve Golson Interview: 'Graphically the 7800 is probably a bit better than the NES, but not quite upto the standard of the Master System..............The 7800 could implement an arcade game better than the NES, but Nintendo was'nt trying that;it did'nt do Donkey Kong over and over.Instead it did Mario platform games'

 

He also talked of the 7800 games development process 'It was generally small teams-one or 2 people per game.Some general work shared by all-we had sound/music specialists'.

[phoenixdownita]

Yes, the above among other reasons - some of which the details are more complex; regardless, the above is indeed a huge factor.

 

 

See this:

 

7800_Super_Cart.PNG

 

256, 512 & 1024k carts were to be made available to the 7800. The highest we received was 144.

 

....

Those are kbits not kBytes, the 1024Kb is a 128KB. A 144KB cart is a 128KB that instead of 16KB of RAM at 4000-7fff has an extra 16KB of ROM.

 

Now truth be told the Commando PCB was made it so it could support either 8 16K pages (128KB) or 32 16K pages (512KB) .... so it was possible to have 512KB of ROM and a Pokey.

32 pages are addressable with only 5 bits so it would be almost trivial to extend the banking to support 8 times that amount (4MB total) but nobody bothered.

 

Finally it's not too hard to extend it further and split the space in ROM/RAM, even the 512KB could have had the first 256B are ROM and the rest as RAM if need be, although the base Commando design did not account for that.

 

 

I'd like to bring one point to the table that is missing:

regarding extra gfx hardware, the NES desginers had the genious idea to have the required gfx memory signals on the cart slot so they could extend it as they saw fit, the 7800/SMS unfortunately not so much. The NES in a way has a design that was inherited also by the NeoGeo in which all the various chips got to expose their buses on the cart slots allowing for far greater flexibility (extra banking for the gfx only etc...etc....).