Re: Writing .cpu file for Z80

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

Hi,
Today I try to implement 0xCB prefixed instructions. I add next
instructions:
(dnf f-0  "whole byte 0" ((MACH z80) all-isas) 7 8)
(dnf f-1  "whole byte 1" ((MACH z80) all-isas) 15 8)
(dnf f-1x "byte 1 field x, bits 7-6" ((MACH z80) all-isas) 15 2)
(dnf f-1y "byte 1 field y, bits 5-3" ((MACH z80) all-isas) 13 3)
(dnf f-1z "byte 1 field z, bits 2-0" ((MACH z80) all-isas) 10 3)
(dni rlc-mhl    "rotate left cyclic" (all-isas) "rlc (hl)" (+ (f-0 #xCB)
(f-1x 0) (f-1y 0) (f-1z 6)) () ())
(dni rlc-r      "rotate left cyclic" (all-isas) "rlc $rs1" (+ (f-0 #xCB)
(f-1x 0) (f-1y 0) rs1) () ())
(dni rrc-r      "rotate right cyclic" (all-isas) "rrc $rs1" (+ (f-0 #xCB)
(f-1x 0) (f-1y 1) rs1) () ())

And disassembler disassemble all CB prefixed instructions as RLC <r>. So it
looks like explicit field value is not work. Next I see, what is generated
for these instructions in the z80-opc.c file:
/* retn */
  {
    { 0, 0, 0, 0 },
    { { MNEM, 0 } },
    & ifmt_retn, { 0x132 }
  },
/* rlc $rs1 */
   {
     { 0, 0, 0, 0 },
    { { MNEM, ' ', OP (RS1), 0 } },
    & ifmt_rlc_r, { 0xcb }
   },
 /* rlc (hl) */
   {
     { 0, 0, 0, 0 },
     { { MNEM, ' ', '(', 'h', 'l', ')', 0 } },
     & ifmt_rlc_mhl, { 0xd1 }
    },

Why fields of different bytes are OR'ed?!?

Next, I try to specify following decode-splits for ISA:
  (decode-splits
    (f-y () ((s-reg8 (0 1 2 3 4 5 7)) (s-mhl (6))))
    (f-z () ((s-reg8 (0 1 2 3 4 5 7)) (s-mhl (6))))
  )
But CGEN fails with error:
machs:   all
isas:    all
options:
trace:
diags:
Including file ../../opcodes/../cpu/simplify.inc ...
ERROR: Wrong type argument in position 2: 3
No backtrace available.

decode-splits is present only one arm.cpu file, but it commented out. Is it
works?

Best regards,
Sergey Belyashov

вт, 24 мар. 2020 г. в 00:44, Sergey Belyashov <sergey.belyashov@gmail.com>:

> Hi,
> I trying to write .cpu file for Z80. Now I stopped in place, how to
> implement multibyte opcodes. Z80 instructions may have size from one byte
> to four bytes:
> <opcode> [<imm8>|<imm16>]
> <0xED> <opcode> [<imm8>|<imm16>]
> <0xCB> <opcode>
> <0xDD/0xFD> <0xCB> <disp8> <opcode>
> <0xDD/0xFD> <opcode> [<imm8>|<disp8>|<imm16>]
> <0xDD/0xFD> <opcode> <disp8> <imm8>
>
> First format is implemented, now I try second one. Starting from simple
> instruction RETN (ED 45):
> (dnf f-0 "whole byte 0" ((MACH z80) all-isas) 7 8)
> (dnf f-1  "whole byte 1" ((MACH z80) all-isas) 15 8)
> (dni retn       "return from NMI handler" (all-isas UNCOND-CTI) "retn" (+
> (f-0 #xED) (f-1 #x45)) () ())
>
> But disassembler do not disassemble 0xED 0x45 sequence. I try declare
> opcode as one 16-bit field, but CGEN fails:
> > Error: Instruction has opcode bits outside of its mask.
> > This usually means some kind of error in the instruction's ifield list.
> > base mask: 0xffff, base value: 0xed45
> > field list: (f-xx 15 16)
>
> What I'm doing wrong?
>
> whole .cpu file is available here:
> https://github.com/b-s-a/binutils-gdb/tree/z80-cgen/cpu
>
> Best regards,
> Sergey Belyashov
>