Re: Writing .cpu file for Z80

[Sergey Belyashov <sergey.belyashov@gmail.com>]

Hi
Thank you.
About sufficies. Short sufficies (.s, .l, .is, .il) should be converted to
the full one by assembler using ADL (acronim for address & data long) mode
state, which is set by programmer (command line options or directive
.assume ADL=1 or .assume ADL=0), so these short sufficies cannot be just
brutforced...

Another question. Z80 instruction set uses same mnemonic for completely
different (comparing to other cpus) instructions:
LD A,n ; 8-bit load immediate
LD HL,nn ; 16-bit load immediate
LD A,(nn) ; 8-bit direct memory load
LD (IX+5),A ;8-bit indirect indexed memory store
LD (nn),HL ;16-bit direct memory store...
Can it cause ASM parser issues?

Best regards,
Sergey Belyashov


сб, 22 февр. 2020 г., 18:11 Frank Ch. Eigler <fche@redhat.com>:

> Hi -
>
> > The Z80 CPU uses prefix opcodes to change opcode tables and operation
> > registers. For example, <0x21 0x34 0x12> is "LD HL,0x1234", but <0xdd
> 0x21
> > 0x34 0x12> is "LD IX,0x1234". Do I need write both instructions or is it
> > possible to write rule which selects proper instruction set or extract
> > correct register index?
>
> Consider writing prefix opcodes as a normal part of the instruction
> (so include them in the base-insn-bitsize).  So you'd need two
> separate instructions, one with and one without.  You may be able to
> use cgen macros to generate both flavours from one piece of
> declaration.
>
>
> > Z80 has special rule to form indirect memory operations using index
> > registers. There immediate offset is always third byte of instruction.
> For
> > example: <0xdd 0x34 0x12> is "INC (IX+0x12)", <0xfd 0x36 0xfe 0xab> is
> "LD
> > (IY-0x02),0xAB"... But there are "strange" instructions, where index is
> > placed before opcode itself: <0xdd 0xcb 0x10 0x1e> is "RR (IX+0x10)"
> (<0xcb
> > 0x1e> is "RR (HL)", <0xcb> is opcode prefix, which select another opcode
> > table) and undocumented one <0xdd 0xcb 0x10 0x1f> "RR (IX+0x10),A".
> Should
> > I write 2 instructions types?
>
> Probably, if the same operands are not in the same place.
>
>
> > eZ80 uses four opcode prefixes (.SIS, .SIL, .LIS, .LIL) which set
> operation
> > mode (.IL - long instruction (24 bit immediate), .IS - short instruction
> > (16 bit immediate), .S - 16 bit processing, .L - 24 bit processing):
> <0x40
> > 0x21 0x34 0x12> is "LD.SIS HL,0x1234" and <0x5b 0x21 0x56 0x34 0x12> is
> > "LD.LIL HL,0x123456".  These prefixes can be applied to all instructions
> > (but it has no sense for part of instructions). Moreover, assembler
> should
> > support short mode of instructions (.S, .L, .IS, .IL), which is completed
> > by assembler depending on compiling mode (ADL or Z80). Should I generate
> > all possible combinations (9 x instruction_set)? Is there more correct
> > solution?
>
> You may be able to represent tehse opcode prefix bytes as an operand,
> and have a special asm parser/printer that sets them from the .SIS etc
> mnemonic suffix.  Or you can go brute-force and generate the family of
> 9 (!) instructions with a cgen macro.  (There may be other ways too.)
>
> - FChE
>
>