cfSetVolume

; =============== S U B	R O U T	I N E =======================================
; Sets track volume.
;
; Has one parameter byte, the volume.
;
; For FM tracks, this is a 7-bit value from 0 (lowest volume) to 127 (highest
; volume). The value is XOR'ed with 7Fh before being sent, then stripped of the
; sign bit. The volume change takes effect immediatelly.
;
; For PSG tracks, this is a 4-bit value ranging from 8 (lowest volume) to 78h
; (highest volume). The value is shifted 3 bits to the right, XOR'ed with 0Fh
; and AND'ed with 0Fh before being uploaded, so the sign bit and the lower 3
; bits are discarded.
;
;loc_C85
cfSetVolume:
		bit	7, (ix+zTrackVoiceControl)		; Is this a PSG channel?
		jr	z, +							; Branch if not
		; The following code gets bits 3, 4, 5 and 6 from the parameter byte,
		; puts them in positions 0 to 3 and inverts them, discarding all other
		; bits in the parameter byte.
		; Shift the parameter byte 3 bits to the right
		srl	a
		srl	a
		srl	a
		xor	0Fh								; Invert lower nibble's bits
		and	0Fh								; Clear out high nibble
		jp	zStoreTrackVolume
; ---------------------------------------------------------------------------
+
		xor	7Fh								; Invert parameter byte (except irrelevant sign bit)
		and	7Fh								; Strip sign bit
		ld	(ix+zTrackVolume), a			; Set as new track volume
		jr	zSendTL							; Begin using new volume immediately