Format of MODPARM Structure:
Offset	Size	Description	)
 00h	WORD	signature 504Dh ("MP" = Modparm)
 02h	BYTE	output device (see #02962 at INT 2F/AX=8221h)
 03h	WORD	segment of start of main module (pattern) data
 05h 31	WORDs	segment of start of sample numbers 1-31
 43h	BYTE	pattern at which to start playing (00h to 7Fh)
 44h	BYTE	function
		00h play from pattern [offset 43h] until end of the song
		01h play indicated pattern [offset 43h] only
 45h	BYTE	Machine speed
		00h 10-12Mhz
		01h 12-25Mhz (default)
		02h 25Mhz+
		03h mix speed 10kHz (fast 8Mhz machines)
		04h mix speed 12kHz (10Mhz machines)
		05h mix speed 13kHz
		06h mix speed 8kHz (test for 8Mhz machines)
 46h	BYTE	allow >64k sample playing
		80h MOD has samples >64k in it
		else all samples in MOD are <64k
Notes:	Main module data and all samples must start on segment boundaries.
	In version 2.00 (ONLY) this function carries on playing (works in
	  the background)
SeeAlso: #02961