Michael J. Mahon wrote:
Ed Eastman wrote:Again, to build a larger ram card means dulpication or bypassing the Memory manager/CYA.Again, to clarify, I thought that the memory manager was compatible with 8MB of RAM (though DMA is not), and that going into the "ROM" space required changes to the memory manager. Did I get it wrong? ... who cares much about Apple's idea of ROM space--unless they cheated in the hardware on the ROM select decoding...
Software wise, the GSOS memory manager is able to deal with up to 8M ram. The CYA hardware only deals with 14 bits (4M) of address/select lines at the memory slot. You are able to bypass this somewhat because 8 data lines and 8 lower address lines are also at the slot. If you recall, the 8 high address bits are sent out the data line and are latched and recoded in the CYA chip to steer lower addresses to the motherboard RAm and higher 'banks to the lower part of the RAM card. Ram card memory lowerst 64K 'bank' is always the next bank above the main board RAM. So the higher address lines provided to the card are not necessarily the same as what the CPU address lines are 'showing'.
Now someone more clever than myself could easily make a 16M Ram card that runs on the slow memory slot that has 16M Ram by ignoring the select lines and watching the addresses coming directly off the data lines. But that would make it an incompatible hybrid that current DMA cards would not work with. And so you might as well make it faster and drop an accelerated CPU on it that will run at the speed of the RAM. Again, only synching to MB clock for screen memory and Slot access, and when slow mode is set at speed softswitch. Any of the good emulators could provide 'watchdog' code to slow it down also during DOS I/O. (ie Slow emulator while drive is on and for several ms after drive goes off.)
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!
Are you listening Retrosystems?!? Hans? Jerri?? Apple??I'll shut up and go work on the thing with no name. It hasn't been touched since Kfest. (Who has time??)
Thankx, Ed