I have gotten the best results by writing the entire routine in assembly and
then linking it with C code. The calling convention isn't well documented,
but not hard to understand by looking at the list files.
Here is a sample routine that takes a single 16 bit argument and returns a
32 bit result:
;; uint32_t core_read (uint16_t addr);
_core_read:
push ix
ld ix,#0
add ix,sp
ld a, 4(ix)
out (reg_addr0), a
ld a, 5(ix)
out (reg_addr1), a
ld a, #1
out (reg_control), a
;; get return value
in a, (reg_rd_data0)
ld l, a
in a, (reg_rd_data1)
ld h, a
in a, (reg_rd_data2)
ld e, a
in a, (reg_rd_data3)
ld d, a
pop ix
ret
On Tue, Dec 1, 2009 at 3:50 AM, Indy Sams <i...@driftsolutions.com> wrote:
> Hello,
>
> I needed a Port I/O routine for the Z80 that would accept the address as a
> parameter, so I wrote 2 functions with inline ASM to do it. I would have
> used sfr, but the addresses need to be passed as a parameter (ie. I can't
> just #define or hardcode them).
>
> I'm pretty new to ASM, and with all the warning in the manual about
> protecting the registers I just wanted to check with some experienced people
> to see if these functions looked OK. They do work fine under emulation,
> haven't tried them on real hardware.
>
> //these 2 are outside of the functions so the symbols will be seen by the
> ASM code
> static uint8 io_val;
> static uint8 io_addr;
>
> uint8 io_read(uint8 addr) {
> io_addr = addr;
> _asm
> push af
> push bc
> ld bc, (_io_addr)
> in a, (c)
> ld (_io_val), a
> pop bc
> pop af
> _endasm;
> return io_val;
> }
>
> void io_write(uint8 addr, uint8 val) {
> io_addr = addr;
> io_val = val;
> _asm
> push af
> push bc
> ld a,(_io_val)
> ld bc,(_io_addr)
> out (c),a
> pop bc
> pop af
> _endasm;
> }
>
> Best regards,
> Indy Sams
> mailto:i...@driftsolutions.com
>
>
>
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