Amiga 1000 pseudo fast ram

[remz]

Hi everyone,

Sorry if this was already asked before, but I just thought of that when ready about the fact that Amiga 1000 read kickstart directly from floppy into a special "write once RAM".

With that in mind, my question is:
Would it be technically possible to code game which would install itself as a "kickstart" in 256KB, and then that game would be running off that special locked ram which is (probably?) running as fast as fast ram?
This would leave the default 256KB of real chip ram completely free.

Of course this would make such technique only compatible with the amiga 1000; But still I wondered if it was ever done?

[Matt_H]

It has been done, but not often. I have a vague recollection of reading about Dragon's Lair being one of the few games that did this, but I'm not certain.

[bloodline]

I’ve not really spent much time looking at the Write once RAM daughter board on my A1000, but I do know that the RAM chips on there are DRAMs… if the board doesn’t have any hardware to refresh those chips (it might have), then it will need to use Agnus to refresh them and the ram access speed would be no faster than SlowRAM.

[phx]

It would be the same speed as the Kickstart "ROM", once loaded into the A1000's WOM. But is it really slower than the A500's ROM? Never heard that before...

[Toni Wilen]

It should have real fast ram speeds. It has no connections to Agnus chip ram side bus/signals and 74LS393 (2x4 bit binary counter) probably is used as a refresh counter.

[paraj]

Should be easy enough to measure, right? Maybe there's some extra fun emulation issues with the refreshes

Is it possible to get a >7MHz accelerator board with fast ram for the A1000? In that case wouldn't it have to limit access speed to the "ROM" to whatever the RAM chips support?

[remz]

Originally Posted by Matt_H

It has been done, but not often. I have a vague recollection of reading about Dragon's Lair being one of the few games that did this, but I'm not certain.

Interesting! I read that Dragon's Lair still required kickstart, but it would "kick it off" the Write-Once memory and installed part of its code in there.
That would seem like a clever hackish way to have lower RAM requirements on the 1000 compared to other Amigas.

[TjLaZer]

Dragon's Lair is the only game that I know of that utilized the 256k WCS. Yes after a reset you had to reload Kickstart.

[desiv]

Yep, as I remember Dragon's Lair required 1M RAM unless you had an Amiga 1000, then 512k would work because it used the WOM..
That was nice.. ;-)

[NorthWay]

IIRC Toni showed a trick (that he had found?) that opened up the WOM for writing again. I wish I had it saved to file...

[remz]

Originally Posted by desiv

Yep, as I remember Dragon's Lair required 1M RAM unless you had an Amiga 1000, then 512k would work because it used the WOM..
That was nice.. ;-)

OMG you are absolutely right!

I don't remember that detail back in the days. How peculiar!

[mark_k]

Originally Posted by NorthWay

IIRC Toni showed a trick (that he had found?) that opened up the WOM for writing again.

A-Max has a special bootblock that write-enables the Kickstart RAM so it can be used for Mac emulation.

Also see DumpA1000BootROM on Aminet.

[Crispy]

Originally Posted by NorthWay

IIRC Toni showed a trick (that he had found?) that opened up the WOM for writing again. I wish I had it saved to file...

Opening up the WOM for writing is just a matter of resetting the machine with a call to the Kickstart code rather than to the boot ROM code. After reset, the WOM will be write enabled. If needed, it can then be write protected by writing to any address in the range from $f80000 to $fbffff.

DoReset     lea     ResetCode(pc),a5
            movea.l _AbsExecBase,a6
            jsr     _LVOSupervisor(a6)
            CNOP    0,4

ResetCode   lea.l   $fc0002,a0
            nop
            reset
            jmp     (a0)