20 Jul
2006
20 Jul
'06
9:38 a.m.
Jules Richardson wrote:
Hmm, if I'm thinking right, all I need to do is
invert A7 from the ISA
BUS before it goes through the selection circuitry, and that'll plonk
the FDC at a base address of 0x370 rather than 0x3f0. Does that sound
sensible? There's even an unused NAND gate on the board that I can use
to do the inversion if so.
I think that should work...
... and I'm not sure if I need to change the IRQ and DMA lines too. Maybe the
primary and secondary FDCs in a PC can co-exist on the same IRQ and DMA
channel [1] (and indeed this seems to be implied by the linux floppy driver -
although it can be told that a second FDC exists at a different port address,
the IRQ and DMA params seem tied to the driver instance, rather than to a
particular FDC controller)
[1] which presumably has potential to screw up if you try to access both FDCs
in the system "at once".
There's enough spare space on the board that I can fit in some homebrew
jumpers to change IRQ and DMA channel if needs be...
cheers
Jules