CD32 Extended ROM switch modification possible?

[Whitesnake]

Are there any simple straight forward modifications available that can disable the Extended ROM in the CD32 via a toggle switch?

I know the CD32 has a 1MB ROM chip which contains both the 3.1 Kickstart and CD32 Extended ROM.

I'm guessing that the Extended ROM is stored the in the upper 512k of the 1MB ROM, The question is can it be disabled and turned back on.

I'd like to do this modification without installing another chip in the empty slot next to the current ROM if at all possible and avoid cutting traces or anything that isn't irreversable.

[Toni Wilen]

Bending one ROM address line pin and connecting it to +5v should do it but finding the correct pin isn't that simple because AFAIK CD32 ROM contents are "interleaved", it is not simple merge of two ROMs (extended + KS ROM, in this order). Normally it would have been highest address pin.

[checking what UAE does..]

Ok, low 512k of ROM has low words and high 512k of ROM has high words, highest address pin selects upper or lower word, which should mean second to last address pin should be the one that selects logical upper (KS) or lower (Ext) 512k.

ROM Address 0: byte 0
Address 1: byte 1
Address 2: byte 4
Address 3: byte 5
Address 4: byte 8
...
Address 524288: byte 2
Address 524299: byte 3
Address 524300: byte 6
..

I am not 100% sure = no pin numbers included

[Whitesnake]

Thanks for the quick informative reply Toni.

So that would be A18* on the 1MB ROM chip if I'm understanding you correctly?

http://www.amigawiki.org/dnl/schematics/CD32_R3.pdf

[Telemachus]

Has anyone tried this with success? the schematics I see online are not clear so I'm not sure what pin it is?

My guess is Pin 20?

[Akira]

What would the advantage of doing this be?

[Arnie]

My guess is that it's something on the same lines as the CDTV where you can disable the CDrom and use it as an A500, i.e. booting to the Workbench screen instead of the CD screen.

[Telemachus]

Originally Posted by Arnie

My guess is that it's something on the same lines as the CDTV where you can disable the CDrom and use it as an A500, i.e. booting to the Workbench screen instead of the CD screen.

Correct, CD32 extended kickstart takes up more ram and creates incompatibilities.

The CD32 does not have a jumper like the CDTV.

[Whitesnake]

Just for reference, Supplying +5v to PIN 20 A18*, or grounding PIN 21 A19* don't work and neither does grounding PIN 20.

So I'm not even sure if this is possible or if the contents of the 1MB ROM are stored in a way that doesn't allow you to make a selection.

[alexh]

The CDTV used a regular, off the shelf, 16-bit Kickstart 1.3 rev34.5 plus an extended ROM.

Does the CD32 use a regular 32-bit Kickstart 3.1?

What I am getting at is, if you remove the CD32 extended ROM will the system still operate? Or will it just crash when functions inside the CD32 Kickstart 3.1 try to access it?

[Magic]

I am pretty sure that the CD32 uses a OTP version of this for the Kickstart IC;

http://www.datasheets360.com/part/de...3200?comp=6224

Perhaps the content can be extracted, modified, and tested with WinUAE to further explore the OP's questions?

[FOL]

Originally Posted by Magic

Perhaps the content can be extracted, modified, and tested with WinUAE to further explore the OP's questions?

It can and I have tried numerous times, never got it to work in WinUAE.

[Whitesnake]

Originally Posted by alexh

The CDTV used a regular, off the shelf, 16-bit Kickstart 1.3 rev34.5 plus an extended ROM.

Does the CD32 use a regular 32-bit Kickstart 3.1?

What I am getting at is, if you remove the CD32 extended ROM will the system still operate? Or will it just crash when functions inside the CD32 Kickstart 3.1 try to access it?

The only information I can go by is Kickstart v3.1 rev 40.60 (1993)(Commodore)(CD32).rom boots on it's own on WinUAE and asks for a floppy disk without the Extended Rom.

The problem here is both kickstart and extended are on the same 1x 1MB rom chip, Seems many people think the CD32 has two rom chips in it.

[Toni Wilen]

Yeah, CD32 has single 16x512K rom chip. (Only AGA Amiga that has 16-bit ROM data path). Schematics shows "optional" 32-bit/2 chip configuration only.

I think it is A17, not A18. (because addressing is word based, not byte)

Only unmodified non-deinterleaved ROM image works in WinUAE because only way to identify it (so that WinUAE knows that this needs deinterleaving and byteswapping) is to match checksum which only works if image is not modified.

If it is modified, it is assumed to be "normal" 1M image and it is mapped directly, first half to 0xe0 and second half to 0xf8, without byteswapping and deinterleaving.

[FOL]

Originally Posted by Toni Wilen

Yeah, CD32 has single 16x512K rom chip.

Really, as the data in the rom including extended is over 512kb.

[chaos]

FOL: 16x512K is a 1MB ROM.

[FOL]

Originally Posted by chaos

FOL: 16x512K is a 1MB ROM.

Sorry, yes you are correct. I saw the 512 bit and thought we were talking about 512kb rom, my fault for glossing over posts.

@Toni.

So we byteswap it would it work or does it need to be deinterleaved too.

[Telemachus]

Originally Posted by Toni Wilen

Yeah, CD32 has single 16x512K rom chip. (Only AGA Amiga that has 16-bit ROM data path). Schematics shows "optional" 32-bit/2 chip configuration only.

I think it is A17, not A18. (because addressing is word based, not byte)

Only unmodified non-deinterleaved ROM image works in WinUAE because only way to identify it (so that WinUAE knows that this needs deinterleaving and byteswapping) is to match checksum which only works if image is not modified.

If it is modified, it is assumed to be "normal" 1M image and it is mapped directly, first half to 0xe0 and second half to 0xf8, without byteswapping and deinterleaving.

Thanks for the info toni.

I lifted pin 19 a17 and attached +5v to it and it just stopped it booting and caused strange on screen graphics I tried grounding it and that did not work either?

Has anyone else had any success with this ?

[Shadowfire]

2x 1MB roms = 2MB ROM space.

$E0000000-$E7FFFFFF rom
$F8000000- $FFFFFFFF rom

CS* (rom) = A(23 downto 20)= "11100" or A(23 downto 20) = "11111"
Two roms are interleaved for 32-bit data bus.
ROMS accept A(21 downto 2) for addressing.
Image for kickstart @$F8000000 will be accessed when A(21:20) = "00".
Pulling pins 42 and 1 down to ground on both IC's will mirror kickstart @ $E0000000 and cause extended rom to vanish, but won't kickstart scan that area for ROMTAGS and make duplicate entries for ROM resources during initialization?

[Telemachus]

Originally Posted by Shadowfire

2x 1MB roms = 2MB ROM space.

$E0000000-$E7FFFFFF rom
$F8000000- $FFFFFFFF rom

CS* (rom) = A(23 downto 20)= "11100" or A(23 downto 20) = "11111"
Two roms are interleaved for 32-bit data bus.
ROMS accept A(21 downto 2) for addressing.
Image for kickstart @$F8000000 will be accessed when A(21:20) = "00".
Pulling pins 42 and 1 down to ground on both IC's will mirror kickstart @ $E0000000 and cause extended rom to vanish, but won't kickstart scan that area for ROMTAGS and make duplicate entries for ROM resources during initialization?

Both IC's?

[Shadowfire]

I don't have one in front of me, but the schematic is showing two 512K x 16-bit roms (D0-D15 and D16-D31). Is there only one ROM on your machine? If so it must be in U6A, can you tell me which of R596-R599 is installed?