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Added assembly level function to set cbm working screen along C prototype

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mc78 2024-08-26 00:41:38 +02:00
parent a633e1060d
commit bc4c36579a
2 changed files with 38 additions and 0 deletions
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10
include/cbm.h
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@ -313,5 +313,15 @@ void __fastcall__ cbm_closedir (unsigned char lfn);
/*****************************************************************************/
/* Supplemental cbm functions */
/*****************************************************************************/
int __fastcall__ cbm_set_working_screen(unsigned char screen_hi);
/* Sets the address of the working screen (no switching of viewport) to screen_hi*0x100.
Checks, if the screen_hi is a multiple of 4. If not, fails with EXIT_FAILURE. */
/* End of cbm.h */
#endif

28
libsrc/cbm/workingscreenaddr.s Normal file
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@ -0,0 +1,28 @@
;
; Stefan 'MonteCarlos' Andree, 26.08.2024
;
; int __fastcall__ _set_working_screen(unsigned char screen_hi);
;
.include "cbm.inc"
.include "c64.inc"
.export _cbm_set_working_screen
_cbm_set_working_screen:
tax
and #3
bne @error
stx SCREEN_HI
sec
jsr PLOT ; Get cursor position ...
clc
jsr PLOT ; ... and set it again to update address of char below cursor with new hi-byte
lda #0
tax
rts
@error:
lda #$ff
tax
rts