Brad Boyer <flar <at> allandria.com> writes: > On Mon, Apr 16, 2012 at 07:50:33PM +1200, Michael Schmitz wrote:
> > >So ISA memory space accesses (isa_readX()) are implemented the same as ISA I/O > > >space accesses? That can't work. Or are they not supported? > > > > There's no distinct 'IO' or 'memory' space on the ROM port adapter, > > it's all memory mapped on ROM port addresses. How does access to ISA > > card mem regions work on ix86? Different address range, or different > > instructions? > > The real x86 instruction set has separate instructions to access any > ports in the IO space (in and out). The instruction also has an access This maps to different lines being driven on the ISA side, see: https://upload.wikimedia.org/wikipedia/commons/3/3d/XT_Bus_pins.png There are I/O read/write and MEM read/write lines (B11‥B14). So you need these that are actually wired up in the adapter. Bascially, “PC” I/O ports have a separate 16-bit¹ address space from the main (originally) 20-bit address space of the main memory (RAM, ROM) which are addressed with different instructions and may behave different when accessed as 8-bit vs. 16-bit slots. ① IIRC, only 12 bit were originally wired or used before the era of the various Local Buses, although according to the 8086 docs that seems to not have been a CPU issue but mainboard design. bye, //mirabilos -- To unsubscribe from this list: send the line "unsubscribe linux-m68k" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
