+;
+; Marco van den Heuvel, 2018-04-27
+;
+
+; unsigned char __fastcall__ set_c65_speed (unsigned char speed);
+;
+;/* Set the speed of the C65 CPU, using SPEED_SLOW will switch to
+; * 1 Mhz mode, SPEED_3X or SPEED_FAST will switch to 3.5 Mhz (fast) mode.
+; *
+; * Note that any value higher or equal to SPEED_3X will switch to fast mode.
+; *
+; * This function will return the actual speed the CPU is at after trying
+; * to set the requested speed, to my knowledge the switching should not fail.
+; *
+; * This function does not check for the presence of a C65/C64DX in C64 mode,
+; * make sure you use 'detect_c65();' before using.
+; */
+
+; unsigned char get_c65_speed (void);
+;
+;/* Get the speed of the C65 CPU.
+; *
+; * Possible return values:
+; * SPEED_SLOW : 1 Mhz mode
+; * SPEED_3X : 3.5 Mhz mode
+; *
+; * This function does not check for the presence of a C65/C64DX in C64 mode,
+; * make sure you use 'detect_c65();' before using.
+; */
+
+ .export _set_c65_speed
+ .export _get_c65_speed
+
+ .include "accelerator.inc"
+
+_set_c65_speed:
+ tay
+ jsr activate_new_vic_mode
+ cpy #SPEED_3X
+ bcs high_speed
+low_speed:
+ and #$BF
+store_speed:
+ sta C65_VICIII_CTRL_B
+ lda C65_VICIII_CTRL_B
+ jmp return_c65_speed
+
+high_speed:
+ ora #$40
+ bne store_speed
+
+_get_c65_speed:
+ jsr activate_new_vic_mode
+return_c65_speed:
+ sta C65_VICIII_KEY
+ and #$40
+ beq speed_is_slow
+ lda #SPEED_3X
+ .byte $2C
+speed_is_slow:
+ ldx #$00
+ rts
+
+activate_new_vic_mode:
+ lda #C65_VICIII_UNLOCK_1
+ sta C65_VICIII_KEY
+ lda #C65_VICIII_UNLOCK_2
+ sta C65_VICIII_KEY
+ lda C65_VICIII_CTRL_B
+ rts