i meant because a z64 only has 256 mbit of memory, and dd images have 512. but if it could be done with a new bios, i think i should think again about selling my z64. ^_^
A new BIOS will not get 64DD images working... not even close. To access the game through I/O ports (necessary), there needs to be an interface between the DRAM and N64 to act as a disk head pointer, with the Z64 there of course isn't one. This could be software emulated if the 64DD BIOS and games are severely hacked. For hardware emulation, you would need to more or less emulate the 64DD but replace the mechanical drive with a pointer (up/down counter) which addresses the DRAM. Even if you decode in your own interface (which would mean completely overhauling the Z64), it would surely be more complicated than the Z64's hardware in the first place and since the Z64's logic source is not available, you would have to work around it anyway. Completely ridiculous! Since N64 accesses ROM extremely slowly and predictably, it would be possible to emulate game paks and the 64DD with a fairly big FPGA and compact flash (or other fast 16-bit interface) and this would be more economical and smart project than attempting and failing to modify a Z64 (or any other backup device)
I wasn't actually talking about you subbie =) it was a general point about many who approached me but eventually lost interest as it would seem. In your case, I m aware that you ve had professional obligations taking more time than you expected =)
If I remember right, a while back Valeryia Pudova (gal who made first N64 home-brew backup unit) said that interfacing to a CF card versus DRAM was possible, because the N64 PI bus very slow... slower than either the SNES or NES actually, because the CPU executes from RDRAM, not ROM. In fact I'm building something like this myself... If this turns out not to work (who knows if a 48mhz 8051 polling the bus is enough) then I'm just stuck with a nice protoboard
Slower than a SNES? ? That cant be! Its a 100Mhz RISC CPU, the bus should be somewhat around 66Mhz? http://www.futuretech.blinkenlights.nl/prod_overview_book.html#bus_interface ->System interface. See ?
Yes, much slower than a SNES. The SNES has one bus and it accesses the bus on every cycle. The 90Mhz N64 couldn't do that or the ROM would need to respond in 11ns! That's difficult to achieve today much less 12 years ago. Just like PC BIOS, the ROM gets loaded into RAM and run from there. N64 ROM isn't even conventional ROM, it's address/data multiplexed and hi/lo address/data word multiplexed to reduce the pin count.
Uhm..but ROM data get xferred via DMA to RDRAM, so it cant be that slow anyway..maybe for random accesses, but since its designedto do BURST reads it really should be fast! And surely not slowlier than a SNES one...sorry but sounds really strange to me...
