The speed impact on CPU of ZERO Fast RAM A1200/CD32

[ImmortalA1000]

I have heard many times from some people that without Fast RAM the CPU is blocked about 50% of the time it could potentially access Chip RAM.

Is this true, more specifically is it true regardless of whether you only write/modify data from Chip RAM locations or just use any of the custom chips to read data from Chip RAM too?

[Thomas Richter]

Essentially, yes, but the details depend on the number of bitplanes activated, and on the video mode and video bandwidth. "blocked" here means that the CPU does not get access to RAM because custom chip DMA requires access instead and takes priority. The 68020 CPU in the A1200 does have an (albeit tiny) instruction cache that may help to avoid RAM accesses for fetching instructions, but the general problem is still there.

[ImmortalA1000]

Originally Posted by Thomas Richter

Essentially, yes, but the details depend on the number of bitplanes activated, and on the video mode and video bandwidth. "blocked" here means that the CPU does not get access to RAM because custom chip DMA requires access instead and takes priority. The 68020 CPU in the A1200 does have an (albeit tiny) instruction cache that may help to avoid RAM accesses for fetching instructions, but the general problem is still there.

Thanks for confirming the myth with some facts. Sounds like the same sort of explanation I was given.

Seems odd Commodore would sell you a 14mhz 020 that can never run at anything like 14mhz oops. I guess AGA was never designed to be used without Fast RAM and it was rushed through. In hindsight they probably should have stuck 128k 32bit Fast RAM on the A1200/CD32 motherboard as a minimum spec but then there is not one single AGA game engine I've seen that pushed that chipset like Lionheart/Lotus II/Beast 1 pushes my Amiga 1000 on my desk so probably would have made little difference to sales.

Made things like the Blizzard 1220/4 a true bargain, if Commodore had lasted longer they would have been wise to do a bundle with that low cost 28mhz 020 + RAM card like they did in the A500 512k + A501 bundles (Class of the 90s pack?).

[alexh]

It would have made the PCB considerably more expensive if they had made it 1+1

[alexh]

Originally Posted by ImmortalA1000

not one single AGA game engine I've seen that pushed that chipset like Lionheart/Lotus II/Beast 1 pushes my Amiga 1000 on my desk so probably would have made little difference to sales.

Brian the Lion AGA? Jurassic Park AGA? Super Stardust? Xtreme Racing? Slamtilt Pinball? Putty Squad? Roadkill?

[eXeler0]

Originally Posted by ImmortalA1000

Thanks for confirming the myth with some facts. Sounds like the same sort of explanation I was given.

Seems odd Commodore would sell you a 14mhz 020 that can never run at anything like 14mhz oops. I guess AGA was never designed to be used without Fast RAM and it was rushed through. In hindsight they probably should have stuck 128k 32bit Fast RAM on the A1200/CD32 motherboard as a minimum spec but then there is not one single AGA game engine I've seen that pushed that chipset like Lionheart/Lotus II/Beast 1 pushes my Amiga 1000 on my desk so probably would have made little difference to sales.

Made things like the Blizzard 1220/4 a true bargain, if Commodore had lasted longer they would have been wise to do a bundle with that low cost 28mhz 020 + RAM card like they did in the A500 512k + A501 bundles (Class of the 90s pack?).

Commodore being Commodore, the A1200 was built to be cheap but upgradable, it bothers me more that the CD32 was crippled in the same way because a console becomes a fixed hardware target/platform for devs.
I started a thread some year ago about the idea if C should have built the CD32 with 1,5MB chip + 0,5 fast.

[zero]

Originally Posted by ImmortalA1000

Thanks for confirming the myth with some facts. Sounds like the same sort of explanation I was given.

Seems odd Commodore would sell you a 14mhz 020 that can never run at anything like 14mhz oops. I guess AGA was never designed to be used without Fast RAM and it was rushed through. In hindsight they probably should have stuck 128k 32bit Fast RAM on the A1200/CD32 motherboard as a minimum spec but then there is not one single AGA game engine I've seen that pushed that chipset like Lionheart/Lotus II/Beast 1 pushes my Amiga 1000 on my desk so probably would have made little difference to sales.

Made things like the Blizzard 1220/4 a true bargain, if Commodore had lasted longer they would have been wise to do a bundle with that low cost 28mhz 020 + RAM card like they did in the A500 512k + A501 bundles (Class of the 90s pack?).

To expand on Thomas's answer and explain what I think happened at Commodore, I'll start by talking about the CPU and memory access.

On an Amiga the CPU and custom chips share access to chip RAM. The custom chips need to access it to create the video signal and audio. On top of that they will access it for things like the blitter and copper, which most games make heavy use of.

The CPU has to wait for slots where it can access chip RAM. The 020 has a small 256 byte cache for instructions. Since all instructions are at least 2 bytes long, many longer, it can only store fairly short sections of code. However, with careful programming it can make a huge difference to performance. Consider the case where the game needs to process a big chunk of data, like day some 3D vectors or some collision hitboxes. If the code that does all the processing can fit in the cache, the only chip memory access needed is to load and store data. By arranging the code so that it does processing between available chip memory access slots (so-called pipelining) the CPU can run at full speed, while the custom chips also operate at maximum performance.

The problem is that is not all that easy to arrange, and most game developers struggled to even get the blitter working.

As for Commodore, they knew they needed to update the Amiga hardware but AAA wasn't ready, so they did AGA instead. AGA is basically a 32 bit extension to parts of the chipset. I've been thinking for a long time that the A1200 would have been better if it had split the RAM into 1MB chip and 1MB fast, but they decided to make it all chip RAM. The main reason is I think to make the PCB layout simpler and cheaper to produce. Splitting the RAM would have meant more RAM chips, and two busses. It would also have complicated the expansion port design.

[Bruce Abbott]

Originally Posted by ImmortalA1000

Thanks for confirming the myth with some facts. Sounds like the same sort of explanation I was given.

What myth?

Seems odd Commodore would sell you a 14mhz 020 that can never run at anything like 14mhz oops.

But it can. Just plug a RAM board into the trapdoor slot and you get the full 14MHz. Or don't if you don't need to. Even without FastRAM the A1200 is more than twice as fast as an A500, and with 2MB ChipRAM and AGA graphics it's capable of much better games.

I guess AGA was never designed to be used without Fast RAM and it was rushed through.

Not exactly rushed. They were trying to develop a more advanced chipset but had to settle for what they could actually make in a reasonable time frame. If they had started with the lower spec they might have gotten it out sooner.

In hindsight they probably should have stuck 128k 32bit Fast RAM on the A1200/CD32 motherboard as a minimum spec

No, that would be a silly idea. Fast RAM would need a separate controller and space on the motherboard, raising the cost significantly. To make it worthwhile you would want at least 1M Fast, preferably in SIMM slots to allow for further expansion. Then you would still sell the base model without a SIMM, and customers would be lumbered with the higher cost of something they might not need.

Made things like the Blizzard 1220/4 a true bargain, if Commodore had lasted longer they would have been wise to do a bundle with that low cost 28mhz 020 + RAM card like they did in the A500 512k + A501 bundles (Class of the 90s pack?).

Perhaps. But it quickly became clear that what the Amiga really needed to stay in the game was a much faster CPU (and a lot more RAM to go with it). Fast c2p hardware would have helped too. But this was way too expensive for bundling in an A500 replacement package. Better to let customers buy the latest 3rd party cards as they became available.

Today you can plug in a card with 80MHz+ CPU, 128MB+ and perhaps even RTG, to make the A1200 into a powerhouse with performance undreamt of in 1992. This shows the true brilliance of the ChipRAM only design. No messy slow 'Fast' RAM to worry about, and better compatibility with older software in the base configuration.

[AmigaHope]

Originally Posted by zero

Splitting the RAM would have meant more RAM chips, and two busses. It would also have complicated the expansion port design.

Except it already had two busses. Every single Amiga has a dedicated CPU bus, even on the A600 without any connectors to it, it still has one that goes to the ROM.

Real estate on the PCB if they'd designed the form factor for it from the beginning, and even if for some dumb reason they were forced to use a particular form factor before designing the PCB, there's still unused real estate on the A1200 motherboard. Since they'd be buying components wholesale, adding an extra 1M would have added maybe $40 to the price, $50 tops. RAM was a LOT cheaper in 1991 than it was in 1985.

Up to 2x performance improvement for a 7% price increase is a no-brainer, and would have had a far more valuable effect in making sure all software was written to that standard.

[ImmortalA1000]

Originally Posted by alexh

Brian the Lion AGA? Jurassic Park AGA? Super Stardust? Xtreme Racing? Slamtilt Pinball? Putty Squad? Roadkill?

Xtreme racing looks horrible, at least Street Racer looks nice on A1200, Putty Squad looks underwhelming and very A500, nothing much improved on Stardust for A1200 same objects more colourful, Pinball Dreams/Fantasies had that market sewn up and did it better anyway so who cares about pretenders like Slamtilt etc etc and you could do top down racers like Roadkill on an Atari STE let alone a Falcon (the competition). Brian the Lion is also designed by an idiot, too many blind drops so it's unplayable. Banshee looks more crap than 32 colour Battle Squadron blah blah.

Flink on CD32 is probably the only console (i.e. SNES) quality game on the CD32, I don't like platformers anyway but it sure looked the part. 1/hundreds is a poor hit rate for a console though and it never came out on A1200.

We didn't even get a good looking footy game, like ISS on SNES (FIFA on Amiga plays like crap and Sensi/Kick-off graphics look like 8bit).

Your standards are too low, once you see things like Lionheart/Beast 1 (level one/intro level) Turrican 3, Kid Chaos, Lotus II, Soccer Kid running on 1985 technology these are very so-so 1993 games.

Unreal, NOT the dumb Quake knock-off, is still the most impressive textured/scaling graphics 3D engine....why didn't people stick that engine in an AGA rally game (would have looked better than that 486/SNES RAC Rally game that came out but the A1200 version was cancelled due to lack of coding talent lol).

A REAL Amiga 1000 game, one worthy of the memory of Jay and Dave R.I.P., should look like the Megadrive version and sound more like the SNES version.

[ImmortalA1000]

Originally Posted by eXeler0

Commodore being Commodore, the A1200 was built to be cheap but upgradable, it bothers me more that the CD32 was crippled in the same way because a console becomes a fixed hardware target/platform for devs.
I started a thread some year ago about the idea if C should have built the CD32 with 1,5MB chip + 0,5 fast.

I used to say the same thing in the mid 1990s too when I heard the rumours about CPU/no Fast RAM issue. The A1200 should have been that in the first place. I am not sure if Commodore engineers really knew what would happen if you took the A4000 Chipset and put it in a machine with no Fast RAM and no asynchronous CPU clock like the A4000 had via CPU slot cards.

The Megadrive has just 64k RAM for code, and the 256 colour 16 channel sound SNES just 128k. At the very least they should have put a SIMM/DIMM slot for 128k memory we could add in. The N64 had a memory slot and a removeable panel to upgrade the consoles memory.

You wouldn't catch Sega making the Megadrive where if you used the sprites you had to cripple the CPU down to 3.5mhz

2mb Chip RAM promotes crap coding, it's like those writing BASIC programs on C64 with GOTOs up the yin-yang. There are better ways to code and Shadow of the Beast start/intro level visually and sonically knackers EVERY AGA game engine with just 512k RAM so I don't see why 2mb for ECS in A600 was needed.

If Commodore ever wanted to make a CD format that didn't fail what they really needed to do was buy Cinemaware lock stock and barrel for peanuts in 1992 etc when they went bust. This happened after their idiotic mistake of only doing It Came From the Desert CD-ROM for PC Engine CD format lol not even PC CD-ROM like Defender of the Crown they had already done for decent CD machines* think how many CDTVs would have been sold off the back of a decent CD game let alone CD32 which was all disk based hand me down games with poundshop quality audio replacing the MOD tunes of Zool 2 or Super Stardust

*PC Engine is awesome sprite based arcade game hardware, shit for many colour streamed anims via single speed CD-ROM drive with EGA style rubbish reduced colours.

[Seiya]

difference with fast RAM you notice more from 68030 and more. If you try 68030 with Chip RAM only the performance are very bad in comparison with some Fast RAM.

[Lord Aga]

Well, as a rule of thumb, the faster the CPU is, the more crippled it is by the lack of FAST RAM.

Even the humble A500 benefits from the addition of FAST RAM (true FAST RAM, not the pathetic excuse for "FAST" RAM that goes into the trap door slot) that can reach as much as 30% speedup. Of course 130% of slow is still kinda slow, but you can definitely feel the speed increase in Workbench. Windows opening, closing, etc.

[Daedalus]

Originally Posted by ImmortalA1000

Xtreme racing looks horrible, at least Street Racer looks nice on A1200, Putty Squad looks underwhelming and very A500, nothing much improved on Stardust for A1200 same objects more colourful, Pinball Dreams/Fantasies had that market sewn up and did it better anyway so who cares about pretenders like Slamtilt etc etc and you could do top down racers like Roadkill on an Atari STE let alone a Falcon (the competition). Brian the Lion is also designed by an idiot, too many blind drops so it's unplayable. Banshee looks more crap than 32 colour Battle Squadron blah blah.

Just because you didn't like the games, doesn't mean they weren't using the extra capabilities of AGA hardware. There are at least as many OCS/ECS games that one could say are terrible games - does that also mean they're not using the features of OCS/ECS?

Yes, the CPU is constrained, but it can still access chip RAM faster than the A500 can, even without fast RAM. Unfortunately, games written for OCS and ECS would often fail to take advantage of the extra performance available.

[ImmortalA1000]

Originally Posted by Daedalus

Just because you didn't like the games, doesn't mean they weren't using the extra capabilities of AGA hardware. There are at least as many OCS/ECS games that one could say are terrible games - does that also mean they're not using the features of OCS/ECS?

Yes, the CPU is constrained, but it can still access chip RAM faster than the A500 can, even without fast RAM. Unfortunately, games written for OCS and ECS would often fail to take advantage of the extra performance available.

A properly developed Amiga 1000 game sits between Megadrive/PC-Engine and the SNES as viewed by Joe Public (Shadow of the Beast 1,Lotus 2, Turrican 3, Lionheart etc etc). It's not about what I like it's about console quality AAA standard artists/programmers/musicians producing an Amiga game. Maybe Shaun Southern or the other 3 or 4 talented coders could have done something really special with an AGA only game but it never happened and that's all there is to it. Sad reality is 99.99% of people working on published Amiga commercial games should have been stacking shelves in supermarkets.

Not that it has anything to do with the original topic, this is more an issue of lack of effort/talent for AGA games and lack of support when awesome Amiga 1000 compatible games were being made (e.g. Lionheart). We will never know the true potential of AGA until somebody as talented as the guys who wrote Beast 1, Lotus II, Lionheart etc turn up, and in the era of homebrew they never did. Even AGA A1200 2mb demos are a yawnfest.

[Daedalus]

You're still confusing your biased opinions with objective reality, and adding to that a tenuous understanding of the situation. For a start your comparison with console memory is nonsense since every cartridge you insert includes a massive chunk of ROM that contains all the graphics, sound and code your game needs, thus removing the need to load them all into RAM.

[Megalomaniac]

You can't really say "Brian the Lion AGA makes poor use of the A1200 because the gameplay's crap" while praising Shadow of the Beast as an example of the A500's hardware being pushed to its limits. Both were technically stunning but not as impressive to play. And I know Roadkill is 'only' a top-down racer, but what other top-down racer looks that good on an A500, or STE, or SNES or Megadrive?

I always thought the A1200 deserved some onboard fast RAM. You'd pay an extra £50 (1/8 of the cost) to improve the performance by 1/3 by having 1.5Mb chip and 512K fast, as long as it didn't impact the upgrade potential for serious users. It surprises me that developers apparently told Commodore they preferred 2Mb Chip only to 1Mb Chip+1Mb fast. The A1200 for £400 in 1992 was nowhere near as exciting an option as the £$£700 A500 in 1992.

[TEG]

Originally Posted by Megalomaniac

The A1200 for £400 in 1992 was nowhere near as exciting an option as the £$£700 A500 in 1992.

Never thought about it before, but the advertising argument "with Fast RAM" would have been a good commercial leverage.

[Bruce Abbott]

Originally Posted by Megalomaniac

You'd pay an extra £50 (1/8 of the cost) to improve the performance by 1/3 by having 1.5Mb chip and 512K fast,

Evidence?

as long as it didn't impact the upgrade potential for serious users.

But it would, so that's a fail. The amount of Fast RAM you could upgrade the A1200 to was practically unlimited, but Chip RAM was forever limited to what was on the motherboard. My A1200 has 32MB Fast RAM which is almost never limiting, but Chip RAM is a valuable resource that can easily get low. Losing 0.5MB would be devastating.

The logistics of splitting the RAM at 1.5MB is dicy. Each block needs 32 data bits, split into 4 bytes. With 8 bit DRAMs That means a minimum of 8 RAM chips (4 Chip, 4 Fast). But 1.5MB is not a power of 2, so you need at least 8 chips (of 2 different sizes) just to do the Chip RAM, and another 4 chips to do the Fast RAM. It would probably be cheaper to do 2MB Chip and 1MB Fast, or even 2MB Chip and 2MB Fast (since then you only need one type of RAM chip, and can get the larger quantity cheaper).

Then you need a separate DRAM controller to manage the FastRAM, and space on the motherboard for it plus the 8 extra DRAM chips and the wires connecting to them (not the least of your problems with a 32 bit data bus). Bottom line, you're going to need a bigger motherboard - which won't fit in the A1200 case. So what do you do?

Option 1: Bigger case: - More expensive, higher freight costs, less convenient size, might look ugly?

Option 2: Encroach on the trapdoor space:- Limits expansion options, 'cheapening' the design to be more like the hated A600 (which had no room for a faster CPU etc.)

Option 3: Put sockets on the motherboard to expand the RAM, with no trapdoor expansion - on the basis that it should be enough for anyone (like the ST). Instant fail! Nobody likes being told what's enough for them.

It surprises me that developers apparently told Commodore they preferred 2Mb Chip only to 1Mb Chip+1Mb fast. The A1200 for £400 in 1992 was nowhere near as exciting an option as the £$£700 A500 in 1992.

Fast RAM is faster, but less useful. It complicates the design of graphics and sound stuff because you have to copy data from Fast to Chip for the custom chips to see it. The 68EC020 in the A1200 already goes more than twice as fast as the 68000 in the A500, and you have bigger sprites, more colorful dual playfields etc. that are begging for more Chip RAM. If a game needs a lot of stuff in Chip then much of that 1MB Fast RAM might end up going spare while the Chip RAM runs out.

From a marketing perspective, a machine with critical features removed is a hard sell. The A500+ and A600 both were capable of 2MB Chip RAM, so the A1200 having only 1.5MB would be (correctly) perceived as a downgrade. Almost every time a machine was released that had significantly worse specs than its predecessor, the public didn't receive it well - particularly if it couldn't be upgraded to match it. And just being cheaper would not make up for it.

But all previous low-end Amigas came stock with Chip RAM only, so this base configuration was expected. Buyers wouldn't mind because they knew it could be expanded with as much as their hearts desired via the trapdoor slot. They also knew that in future such expansions would become better and cheaper. And how right they were!

By the end of its commercial life the A1200 was being upgraded with an 040 or 060 CPU and up to 128MB Fast RAM, and even dual 68k and PPC CPUs with hardware 3D graphics. Once you got a setup like that, some tiny amount of Fast RAM on the motherboard would be insignificant - possibly just an annoyance since a faster CPU would have to slow down to access it.

[Seiya]

68020 or faster processor without Fast RAM have a bad perfomance in 3D engine with or without textures.
in 2D game Fast RAM have less importance and de facto many AGA platform games run very smooth on stock A1200