[Coco] Above 512k upgrades

[Robert Gault]

John W. Linville wrote:

> On Tue, Aug 14, 2007 at 12:47:22PM -0400, jdaggett at gate.net wrote:
> 
>>On 14 Aug 2007 at 9:08, John W. Linville wrote:
>>
>>
>>>IIRC, isn't there something about the video memory offsets that needs
>>>to be handled as well?  Sorry, I don't have a GIME reference handy to
>>>ask a more specific question...
> 
> 
>>The GIME MMU uses only 6 bits to form the part of the Address from A13 to 
>>A18. Other methods extend the addressing range beyond that. IF you setup 
>>extra memory as blocks of 512K, then you will  have to to little to any 
>>existing software. One approach  is to have essentially super task switching 
>>to where one or more programs can run in their own 512K block.
> 
> 
> Yes, but I think you miss the point of my question.  As I recall,
> if you merely extend the MMU entries to the natural 8-bits then you
> will still have to keep your video in the 0th 512k block.  To be able
> to allocate video frames beyond the first 512k you need a means to
> extend the video addressing as well.
> 
> John

That issue has been handled by extending the the number of vertical 
offset bits into $FF9B. I've got an 8Meg board made by Paul T. Barton 
and I think he may have gotten up to 32Megs but at least 16Megs.