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cc65/libsrc/common/getcpu.s
2018-04-01 13:14:44 -07:00

91 lines
2.8 KiB
ArmAsm

;
; Ullrich von Bassewitz, 02.04.1999
;
; unsigned char getcpu (void);
;
.export _getcpu
; ---------------------------------------------------------------------------
; Subroutine to detect an 816. Returns
;
; - carry clear and 0 in A for a NMOS 6502 CPU
; - carry set and 1 in A for a 65C02
; - carry set and 2 in A for a 65816
; - carry set and 3 in A for a 4510
; - carry set and 4 in A for a 65SC02
; - carry set and 5 in A for a 65CE02
; - carry set and 6 in A for a HuC6280
; - carry clear and 7 in A for a 2a03/2a07
;
; This function uses a $1A opcode which is a INA on the 816 and ignored
; (interpreted as a NOP) on a NMOS 6502. There are several CMOS versions
; of the 6502, but all of them interpret unknown opcodes as NOP so this is
; just what we want.
.p816 ; Enable 65816 instructions
_getcpu:
lda #0
inc a ; .byte $1A ; nop on nmos, inc on every cmos
cmp #1
bcc @L8
; This is at least a 65C02, check for a 65CE02/4510
.byte $42,$EA ; neg on 65CE02/4510, nop #$EA on 65C02, wdm $EA on 65816
cmp #1
beq @L6
; This is at least a 65CE02, check for 4510
lda #5 ; CPU_65CE02 constant
.byte $5C ; map on 4510, aug on 65CE02 (acts like 4 byte nop)
lda #3 ; CPU_4510 constant
nop
bne @L9
; 6502 type of cpu, check for a 2a03/2a07
@L8:
sed ; set decimal mode, no decimal mode on the 2a03/2a07
lda #9
clc
adc #1 ; $01+$09 = $10 on 6502, $01+$09 = $0A on 2a03/2a07
cld
cmp #$0a
beq @L5
lda #0 ; CPU_6502 constant
beq @L9
@L5:
lda #7 ; CPU_2A0x constant
bne @L9
; 65C02 cpu type, check for HuC6280
@L4: ldx #6 ; CPU_HUC6280 constant
.byte $22,$EA ; sax nop on HuC6280 (A=$06, X=$01), nop #$EA on 65C02 (A=$01, X=$06)
bne @L9
; Check for 65816/65802
@L6: xba ; .byte $EB, put $01 in B accu (nop on 65C02/65SC02)
dec a ; .byte $3A, A=$00
xba ; .byte $EB, A=$01 if 65816/65802 and A=$00 if 65C02/65SC02
inc a ; .byte $1A, A=$02 if 65816/65802 and A=$01 if 65C02/65SC02
cmp #2
beq @L9
; check for 65SC02
ldy $F7
ldx #0
stx $F7
.byte $F7,$F7 ; nop nop on 65SC02, smb7 $F7 on 65C02
ldx $F7
sty $F7
cpx #$00
bne @L4
lda #4 ; CPU_65SC02 constant
@L9: ldx #0 ; Load high byte of word
rts