|Did someone say that Advantage cannot be loaded in NoVRAM? Was it me?|
Message #1 Posted by Diego Diaz on 14 Sept 2008, 6:12 p.m.
Sometimes, as you're trying to explain any particular concept you're supposed to know, to someone who's interested in the subject; your brain tries to find some reasoning path in order to make the concept more easily understandable.
Under certain circunstances this leads you to either extend or change your focus on this especific issue and, suddently, you realized that there are a whole new range of possibilities you haven't even conceived before.
Sorry for the long introduction. It comes to the point that, as I was trying to explain (some posts below) the deeply fundamented reasons why Advantage .ROM files *cannot* be used altogether with HEPAX emulation into a NoVRAM module, I saw a small light comming from a narrow gap in my explanation.
Certainly, HEPAX need 4 pages, Advantage needs 3: total 7. NoVRAM has only 6 ROM pages, conclusion: Advantage cannot be burned into NoVRAM's ROM. Period.
Second argument, Advantage is bankswitched, HEPAX RAM does not support bankswitching. Advantage cannot be loaded into NoVRAM's RAM either. Period.
Small gap: *Only* the upper page of Advantage is bankswitched...
And, what if?... we load that lower page into RAM which is not bankswitched... (who cares?) but it IS (and more relevant) *Non-volatile*, placing it into page C at first instance and then COPYROM to page A.
After this, another burning process is required to place both bankswitched images of Advantage's upper page into page B bank 1 and bank two respectively.
Originally page B is reserved for RAM, so I wrote a modified version of the NoVRAM code for that purpose. This sacrifies RAM pages A and B in order to gain the required space for the Advantage images.
Page A is still RAM from a phisical point of view but it's seen like another ROM (not bankswitched) ROM page.
In abstract we get a Standard HEPAX (with 8K RAM) + Advantage into a NoVRAM, using pages 8 to C, and one single physical port.
The process is not the most straightforward, but.. IT WORKS! ;-)
And, sincerelly, I've enjoyed a lot...
Best wishes from the Canaries.