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65 lines
1.8 KiB
ArmAsm
65 lines
1.8 KiB
ArmAsm
;
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; Marco van den Heuvel, 2018-04-14
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;
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; unsigned char __fastcall__ set_c64dtv_speed (unsigned char speed);
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;
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;/* Set the speed of the C64DTV, using SPEED_SLOW will switch to
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; * slow mode, SPEED_2X or SPEED_FAST will switch to fast mode.
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; *
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; * Note that any value higher or equal to SPEED_2X will switch to fast mode.
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; *
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; * This function will return the actual speed the CPU is at after trying
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; * to set the requested speed, to my knowledge the switching should not fail.
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; *
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; * This function does not check for the presence of the C64DTV,
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; * make sure you use 'detect_c64dtv();' before using.
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; */
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; unsigned char get_c64dtv_speed (void);
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;
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;/* Get the speed of the C64DTV.
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; *
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; * Possible return values:
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; * SPEED_1X : slow mode
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; * SPEED_2X : fast mode
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; *
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; * This function does not check for the presence of the C64DTV,
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; * make sure you use 'detect_c64dtv();' before using.
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; */
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.export _set_c64dtv_speed
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.export _get_c64dtv_speed
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.include "accelerator.inc"
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_set_c64dtv_speed:
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cmp #SPEED_2X
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bcs high_speed
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low_speed:
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ldx #C64DTV_Slow
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set_speed:
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.byte $32,$99 ; SAC #$99 set accumulator to reg 9 (cpu control)
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txa ; (re)set skip and burst bits
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.byte $32,$00 ; SAC #$00 set accumulator back to reg 0
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jmp _get_c64dtv_speed
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high_speed:
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ldx #C64DTV_Fast
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bne set_speed
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_get_c64dtv_speed:
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.byte $32,$99 ; SAC #$99 set accumulator to reg 9 (cpu control)
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tax
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.byte $32,$00 ; SAC #$00 set accumulator back to reg 0
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txa
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and #C64DTV_Fast
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bne in_fast_mode
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lda #$00
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.byte $2C
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in_fast_mode:
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lda #$01
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ldx #$00
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rts
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