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38 lines
1.0 KiB
ArmAsm
38 lines
1.0 KiB
ArmAsm
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; Ullrich von Bassewitz, 02.04.1999
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;
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; unsigned char getcpu (void);
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;
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.export _getcpu
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; ---------------------------------------------------------------------------
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; Subroutine to detect an 816. Returns
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;
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; - carry clear and 0 in A for a NMOS 6502 CPU
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; - carry set and 1 in A for some CMOS 6502 CPU
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; - carry set and 2 in A for a 65816
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;
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; This function uses a $1A opcode which is a INA on the 816 and ignored
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; (interpreted as a NOP) on a NMOS 6502. There are several CMOS versions
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; of the 6502, but all of them interpret unknown opcodes as NOP so this is
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; just what we want.
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.p816 ; Enable 65816 instructions
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_getcpu:
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lda #0
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inc a ; .byte $1A
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cmp #1
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bcc @L9
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; This is at least a 65C02, check for a 65816
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xba ; .byte $eb, put $01 in B accu
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dec a ; .byte $3a, A=$00 if 65C02
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xba ; .byte $eb, get $01 back if 65816
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inc a ; .byte $1a, make $01/$02
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@L9: ldx #0 ; Load high byte of word
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rts
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