Gold Card ROM Shadowing

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Peter
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Gold Card ROM Shadowing

Postby Peter » Sun Dec 01, 2013 10:59 pm

Is there any information, at which address (if any) the Gold Card can directly access the ROM area originally located at $C000 to $FFFF?

In normal operation, this address range seems to be shadowed in RAM, and therefore not usable to access real hardware (for some Gold Card PLD revisions).

I'm aware that the system ROM $0 to $BFFF must be shadowed as there are OS patches. However there are hardware devices like Romdisq, which use $C000 to $FFFF for register access, so I hoped this upper area wouldn't use shadowing. On my Gold Card, the QL-SD driver worked fine, which seemed to support my assumption at first. However, another Gold Card appeared which seems to shadow.

Thanks, Peter


skagon
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Re: Gold Card ROM Shadowing

Postby skagon » Mon Dec 02, 2013 12:33 am

I suppose we *could* do a Gold Card ROM disassembly and see what the hell it's doing on system boot; i.e. which addresses it's copying where and which patches it's applying to them.
It's still 68k machine code... is it worth the trouble, though?


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dilwyn
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Re: Gold Card ROM Shadowing

Postby dilwyn » Mon Dec 02, 2013 8:17 am

skagon wrote:I suppose we *could* do a Gold Card ROM disassembly and see what the hell it's doing on system boot; i.e. which addresses it's copying where and which patches it's applying to them.
It's still 68k machine code... is it worth the trouble, though?

Ordinarily I might have replied "No" to this, as it only seems to affect older Gold Cards, or rather Gold Cards with older INGOT 3 PLDs.

However, Peter has put in so much time and effort and probably money too (not to mention Adrian Ives before him) to try to bring QL-SD to market as an affordable mass-storage solution that it would be an absolute shame if the project failed right now.

From what I know of this, it only seems to affect Gold Cards with the older PLD chip, so it could probably be argued that this issue is not too important since it will only affect a tiny majority of Gold Cards. However, equally, if it turns out to be very easy to solve, then great. I guess there's no harm in looking into it to see if a simple solution is possible.

On a more general note, disassembling the Gold Card startup code could well prove useful in future as there is little or no documentation that I know of about this aspect of (Super) Gold Cards.


Dilwyn
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Peter
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Re: Gold Card ROM Shadowing

Postby Peter » Mon Dec 02, 2013 3:55 pm

I should add that the affected Gold Card seems to have an unusual mix of components.
The firmware and the PCB (Red, Issue 3) are newer than my Gold Card (Red, Issue 2), but the PLD (INGOT 3) is older than mine (INGOT 6).

It almost looks like someone put together the card by components which did not originally belong to the same manufacture process.

Apart from disassembling the Gold Card boot firmware, a look into the Romdisq source could also help. Stuart Honeyball was still involved in that project, so I'm pretty sure Gold Card specialties have been catered for.

Tony Firshman, if you read this, would you allow me a look into the sources?


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Peter
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Re: Gold Card ROM Shadowing

Postby Peter » Sat Dec 07, 2013 11:15 pm

The user with the INGOT 3 Gold Card reports that the problem accessing $C000 to $FFFF no longer exists. Please disregard my suspicion of ROM shadowing in this address range.



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