Michael J. Mahon wrote:
Ed Eastman wrote:Yes, I did just say put an accelerator on the Ram card. And put a darned CFA/IDE controller in a selectable slot on the board! DMA that sucker at RAM speed!It would be necessary to have a cable to the processor socket to make such a card work, but that seems acceptable. It would also be tricky to DMA to main board RAM from the memory slot, but if one is writing their own OS, who cares.
Dubbed the AcceleRAM card...First off it should be noted that the DMA is not fully implemented from the slots because the the CYA chip was designed to cripple the IIgs and the 65816's capability so it wold not compete with the Mac.
But I don't think DMA would be tricky at all as this design would break DMA at the slots, right? You'd be bypassing the CYA chip. If you wanted to make it compatible, you could by watching the DMA line from the slots. Trick would be to tap it easily. Now you are looking at 3 plug design, Ram Slot, CPU socket and another slot.
The DMA line is pulled low when you want to access the memory directly from a slot. The CYA chip would want to put out the high address lines on the RAM slot but AcceleRAM ignores them anyway and latches from the data lines per IIgs technical specifications. The built in HD I suggested would not need to worry about it because it'd be right there with a direct link to REAL RAM.
The AcceleRAM card would need to be clocked slowly from the main board with address and data lines provided back to the main board via the CPU connection and Ram slot (Depending on Read or write) only when accessing screen Ram area or soft switches, otherwise it would clock at RAM speed. The CYA would see the CPU on the AcceleRAM card putting and address on the line and act accordingly to mirror the data just like it does now. :) (When synchronized with the main board clock, the AcceleRAM card would be transparent to the CYA, it would be fat dumb and happy.
Again, someone more clever than myself could do this in one of those programmable logic chips, Pal or FPGA, don't ask me, I'm not that clever.
Thankx, Ed