More Chipram

[Karlos]

"Guess what?! I have a fever. And the only perscription is, more chipram!"




;-)

[Karlos]

This is one subject where you really ought to listen to the nay sayers.

Short of building a complete replacement set of custom chip hardware that supports 8MB of chip ram and writing the appropriate OS patches to get it recognised and doing what you can to fix what that breaks in the Z2 space (if it is even possible), it isn't going to happen.

UAE works simply because it doesnt have any real constraints. Real hardware does. Something like a MiniMig style system is the best possibility for this type of thing.

[Karlos]

Dillusional in 4 words:

Eight Megs Chip Ram

[Karlos]

@bloodmoney

You took the image right out of my mind ;-)

"And Leirbag, explore the address space. Explore the address space!"

Leirbag waveing megachip...
"I would be doing myself and this platform a disservice if I didn't expand the hell outta this"

[Karlos]

@leirbag

Since WinUAE emulates 8MB capable hardware. What makes you think it wouldn't patch _any_ kickstart version you provide it with in order to get it recognised?

[Karlos]

@leirbag

I really don't mean to sound harsh here but you just need to accept it. There are people here who have forgotten more about the amiga hardware than you, or I, will ever know. And you are the only person insisting this idea will work.

The thing is, even if I can add 8MB an amiga's Z2 area by hacking away merrily, there are only 21 working address lines gluing it together. 2^21 = 2097152, which oddly enough is 2MB worth of address space. Even if I used lots of really fine wire to add the other 2 I would need to get to 2^23 (8MB), where do I connect them to?

Answers on a postcard...

[Karlos]

@Stopthegop

Look, nobody said that an 8MB chipram capable hardware amiga is impossible per se. You could do it just fine if:

1) You make a replacement chipset capable of accessing the full 8MB
2) rewire entire motherboard to take said chipset, included but not limited to adding extra addressing lines etc
3) Make a patch for the OS so that the 8MB are recognised
4) Find a fix for whatever problems stealing the address space away from other hardware that wants to reside there causes.

If you do all of this, you will find you have essentially replaced the entire system. It wouldn't exactly be an expansion, it would be an entirely new system.

Hmm, guess what WinUAE does...

Something like MiniMig has the potential for this type of thing, but as far as existing classics systems go, forget it. However, if you can find a way to make the existing custom chips sprout more address lines and be able to use them then I will stand corrected on the original point.

[Karlos]

KThunder wrote:

you use a bus snoop chip to decode the upper bits and if anything over 2meg is being accessed it lets the custom chips know

So you get a system with >2MB chipram that can't be used by the custom chips. It also means that things that are supposed to get done, arent, which probably means a crash. How is this useful?

[Karlos]

@KThunder

"So you get a system with >2MB chipram that can't be used by the custom chips" - meaning they can't use the area > 2MB, not  that they can't use any chip ram at all.

The problem is, what happens when the OS allocates chip memory above 2MB space for the bitplane data of a screen you just opened? Your snooper prevents the hardware from doing anything when it tries to fetch the data. So you just get a totally black screen (if you are lucky, I am sure things would crash long before getting even this far) ?

As for using the memory for program code etc, why? This is what fast ram is for.

[Karlos]

Can you give an example of anything the OS specifically puts into chip ram (on any machine having adequate fast ram) that isn't put there so the custom chips can use it for some purpose?

[Karlos]

KThunder wrote:
wait... screens i see what you mean, im thinking in terms of programs but the os could put screens up there couldnt it

The OS would look only for MEMF_CHIP for the displayable bitplane data on your 8MB system. Now if you already gobbled up your lower 2MB with 3 instances of Scala, it isnt going to not allocate it above 2MB if space exists there.

[Karlos]

KThunder wrote:

your stack is in chip ram, so are major parts of the os, as are any old programs and all data concerning what programs are loaded and where they are, multitasking info etc.

Holy smokes, your amiga must be dead slow then. On mine, all this data goes right into fast ram where the 68040 can access it every cycle ;-)

[Karlos]

Nope, I have the following all in fast (and the address ranges to prove it)

Kickstart
Exec
Supervisor Stack Pointer
User Stack Pointer
Vector Base Register

[Karlos]

On UAE its fine because UAE emulates custom chips that were never actually made in real life that are capable of using all 8MB of chip ram. So everything is just fine.

Of course setting 8MB of chip reduces your Z2 space as you might notice. On a real amiga this could be problematic as a lot of expansions want to live there.

[Karlos]

KThunder wrote:
so you guys have nothing in chip ram huh, nothing at all not a single byte used?
what is this thread here for then if noone uses chip ram

Yes we do have stuff in there, just not code. Graphics data, sound data all go there, where the custom chips can make use of it.

Although my graphics data tends to reside in the VRAM of my graphics card. It's only in chip ram when retrogaming ;-)