Added C64 Turbo Master accelerator code and documentation.

libsrc/c64/acc_turbomaster_speed.s

@@ -0,0 +1,63 @@
+;
+; Marco van den Heuvel, 2018-04-30
+;
+
+; unsigned char __fastcall__ set_turbomaster_speed (unsigned char speed);
+;
+;/* Set the speed of the Turbo Master cartridge, using SPEED_SLOW will switch to
+; * 1 Mhz mode, SPEED_4X or SPEED_FAST will switch to 4 Mhz mode.
+; *
+; * Note that any value higher or equal to SPEED_4X will switch to 4 Mhz mode,
+; * any value lower than SPEED_4X will switch to 1 Mhz mode.
+; *
+; * This function will return the actual speed the CPU is at after trying
+; * to set the requested speed, if the speed is different it might indicate
+; * that the hardware switch has locked the speed.
+; *
+; * This function does not check for the presence of a Turbo Master cartridge,
+; * make sure you use 'detect_turbomaster();' before using.
+; */
+
+; unsigned char get_turbomaster_speed (void);
+;
+;/* Get the speed of the Turbo Master cartridge.
+; *
+; * Possible return values:
+; * SPEED_SLOW  : 1 Mhz mode
+; * SPEED_4X    : 4 Mhz mode
+; *
+; * This function does not check for the presence of a Turbo Master cartridge,
+; * make sure you use 'detect_turbomaster();' before using.
+; */
+
+        .export         _set_turbomaster_speed
+        .export         _get_turbomaster_speed
+
+        .include        "accelerator.inc"
+
+_set_turbomaster_speed:
+        tay
+        lda     TURBOMASTER_SPEED_REG
+        cpy     #SPEED_4X
+        bcs     high_speed
+low_speed:
+        and     #$7F
+store_speed:
+        sta     TURBOMASTER_SPEED_REG
+        jmp     _get_turbomaster_speed
+
+high_speed:
+        ora     #$80
+        bne     store_speed
+
+
+_get_turbomaster_speed:
+        ldx     #$00
+        lda     TURBOMASTER_SPEED_REG
+        and     #$80
+        beq     is_slow_speed
+is_high_speed:
+        lda     #SPEED_4X
+is_slow_speed:
+        rts
+