troed wrote: ↑Mon Oct 16, 2017 5:14 pm
The problem lies in the MMU only latching words when it does - and in sync with the GLUE hsync/vsync/blank/DE. However, for a 16MHz boosted machine - a Shifter that understands such a boost could in theory do 320*200*256 (8 bitplanes)
Not really thought about the other signals yet.. I guess the load rate by the MMU is constant, so if we added a extra word or a extra plane, this would mean I think the resolution would actually be lower ? Adding a extra word into the mix would mean some MMU time is taken up with shifting more data as opposed to actual pixels to the screen..I do not really know how it would work out...
But like you say anyway, we have double the throughput from their menu to the shifter, so given the same resolutions, like you say, we could easily have 8-bit planes in low resolution..
Though really if we doubled the bit planes in medium resolution will will be back to distinct colours in medium resolution with a current mods which you have done..
I think the data rate MMU is constant per pixel line, as we see for example with 320 pixels across, we have can have four bit planes, or 640 pixels across for 2 bit planes, the data rate, or the words shifted per line is exactly the same in each case..
Of course now we have MMU running at double speed, we can shift twice as much words and use them as we see fit.. So we could actually shift, again as you say, 320 pixels across with 8 bit planes, or 640 pixels across with four bit planes..
But we also must take into account we was aiming for higher resolutions.. But I guess the MMU overclocked can either go into more bit planes or more resolution, I guess it does not really matter as long as we are tallying up the data throughput correctly.
But really what does actually get set with the MMU that it loads for words at a time ? I would just assume the MMU is not that intelligent, and it is basically just bit banging data from ram into the shifter and just continues doing that over and over.. In which case if the shifter supported a extra bit planes for 32 colours for example, the MMU would just continue to output the data in order as it was before, the of course the shifter would have to process the extra bit plane, which is going to take time, and time would ultimately mean less time outputting pixels.
Overall, as we are still running slightly faster than the stock machine with the double size resolution, I think we could easily squeeze in a 58 plane for all the extended resolutions.. Of course it would need software to support this extra video mode..
I guess as we have lots of extra bits to play with in the register, all sorts of additional combinations of bit planes resolutions could be added. Though we would likely need a bit of hackery and extra address line to the shifter to program the extra colour palettes..
The another slight problem is that it would probably need different dot clock speed also.
My brain hurts now
I know of no such hardware issue.
