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66 lines
1.6 KiB
ArmAsm
66 lines
1.6 KiB
ArmAsm
;
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; Oliver Schmidt, 2012-09-04
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;
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; unsigned char getfirstdevice (void);
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; unsigned char __fastcall__ getnextdevice (unsigned char device);
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;
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.export _getfirstdevice
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.export _getnextdevice
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.import isdisk
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.import opencmdchannel
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.import closecmdchannel
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.importzp ST
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.importzp tmp2
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;------------------------------------------------------------------------------
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; _getfirstdevice
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_getfirstdevice:
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lda #$FF
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; Fall through
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;------------------------------------------------------------------------------
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; _getnextdevice
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_getnextdevice:
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tax
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next: inx
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cpx #$FF
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beq done
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; [open|close]cmdchannel already call isdisk internally but they
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; interpret a non-disk as a no-op while we need to interpret it
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; as an error here
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jsr isdisk
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bcs next
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; [open|close]cmdchannel don't call into the Kernal at all if they
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; only [in|de]crement the reference count of the shared cmdchannel
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; so we need to explicitly initialize ST here
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lda #$00
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sta ST
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stx tmp2
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jsr opencmdchannel
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ldx tmp2
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jsr closecmdchannel
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ldx tmp2
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; As we had to reference ST above anyway we can as well do so
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; here too (instead of calling READST)
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lda ST
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; Either the Kernal calls above were successfull or there was
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; already a cmdchannel to the device open - which is a pretty
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; good indication of its existence ;-)
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bmi next
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done: txa
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ldx #$00
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rts
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