A1000 custom kickstart

trisomie21

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Just trying to see if this idea is technically possible (or even already one ?)

Create a custom 256K kickstart for the A1000 that include an image of a compressed kickstart 2.0 rom
That kickstart decompress the image in fastram and assign it as fastrom.

So once loaded, each reboot would refresh the fastrom from the 256K load ROM.
 
I just tried compressing a KS 2.04 ROM to a RAR file which has quite efficient compression and even it couldn't make it fit in 256kB so it doesn't seem feasible that you could fit it in 256kB when you also need to include the decompression algorithm. The ACA500 does something like this though as it has compressed images of 1.3 and 3.1 on board.

Another thing is the speed of the decompression. How long would you realistically accept to wait on every reboot for the decompression to complete? 5s?
 
I think a custom compressor might have to be used. Assuming most is 68000 code from a C compiler, there might be a better/better and simpler compressor then RAR ?
(Maybe even a 'hand tweaked' compressor... ?)

But if RAR cant make it close to 256K, this might be the biggest barrier to this idea.

5 seconds would be acceptable.
At 100KB decompression speed, this would represent about around 35 instructions executed per byte written? that seem doable with a custom algorithm
 
I think a custom compressor might have to be used. Assuming most is 68000 code from a C compiler, there might be a better/better and simpler compressor then RAR ?
(Maybe even a 'hand tweaked' compressor... ?)

But if RAR cant make it close to 256K, this might be the biggest barrier to this idea.

RAR can get 2.04 down to 264kB and 2.05 down to 273kB. 2.04 to ZIP is 284 kB. Perhaps you could win something by making some assumptions about it being code, but I think that RAR is quite good at defining a good dictionary already.
 
ROM chips are not exactly expensive these days... a 27C160 sells for about 1.50$ on eBay and it can carry 2MBytes. I've used these chips to make triple kickstarts for the A2000 a decade ago.

You can even get a 27C322 which carries 4MBytes for 2$US.

They have more than one chip select line so you can have them tied to specific address lines and choose exactly what address range they will occupy.

The secret in the case of the Amiga 1000 is at what address range you'd want that ROM to show up to avoid conflict. You could easily put all the kickstarts you want in uncompressed form in there and just have your custom kickstart copy the one you choose from the hidden EPROM to FastRAM/fastROM.
 
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I'm not a HW guy at all, but I assume from your post that the 27C322 is a drop in replacement for a chip on the A1000 ?
Like the chip that hold the bootstrap code?

Then I have to ask, is should be also possible to make a custom bootstrap code that load a kickstart for disk or from the ROM itself?

That seem to simple/"clean" of a solution compared to some other A1000 kickstart selector that require jumpers, trace cut, and custom board.
 
@Trisomie21
The 27C160 is almost a drop-in replacement to the A500/A2000 kickstart ROMs. The 27C160 simply has 2 extra pins and I used those 2 pins to chose which kickstart you want in the A2000.

You're not getting away without a custom board and only a good programmer can make you the required bootstrap code.

From your initial post, I assumed you already had an adapter board which allows the use of a normal (1.2 or 1.3 kickstart) in your Amiga 1000.
 
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Is there a drop in replacement, with larger capacity, for the ROM the A1000 use for the bootstrap code ? (assuming they are on sockets?)
I think they total 64K, so did they make any that where 256K ?

chips C252179-01 and C252180-01 seem to be on sockets. And are I think 8bit 32K , total 16bit 64k ?
(But I read that the bootstrap code only uses 8kB)

http://www.bigbookofamigahardware.com/bboah/media/download_photos/a1000mbrev6.jpg

I'm guessing that there must be an obvious reason why non one ever offered rom upgrade for the A1000, even so there where on sockets ?
 
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