rive l is undefined.
drivem	equ	0ffh		; drive m is undefined.
driven	equ	0ffh		; drive n is undefined.
driveo	equ	0ffh		; drive o is undefined.
drivep	equ	0ffh		; drive p is undefined.

	; define disk control variables for system.

hlab	equ	8		; fdc head load: 8=before, 0=after, seek.
stprat	equ	1		; fdc seek rate: 0=3ms, 1=6ms, 2=10ms, 3=20ms.
pctrk	equ	43		; pre-compensation above this track.
ibmtpd	equ	40		; ibm tracks per 5-inch floppy.
rtcnt	equ	10		; fdc read/write, fail retry count.
srtcto-memory command.
fdmawt	equ	016a6h		; memory-to-floppy command.

	; additional system equates.

fresh	equ	1		; bdos fresh disk access bit mask.
eof	equ	1ah		; end of file value.
cr	equ	0dh		; ascii carriage return.
lf	equ	0ah		; ascii line feed.
tab	equ	09h		; ascii tab.
spc	equ	20h		; ascii space.

	; equates for Sector Blocking / Deblocking

	; CP/M to host disk constants

;
blksiz	equ	4096		;CP/M allocation size
hstsiz	equ	512		;host disk sector size
hstspt	equ	16		;host disk sectorsbase dma operations.
	jmp	retsegt		; return offset of memory descriptor table
	jmp	retiobt		; return i/o byte value.
	jmp	setiobt		; set i/o byte value.


	; *********************************************************
	; ******************* cold-start entry ********************
	; *********************************************************


coldstart:

	; initialize system.

	cli				; disable interrupts during ini.
	mov	ax,cs			; use segment passed with jmpf.

	mov	ss,ax			; stack segment.
	to match.

	if	(not loader) and sizmem

	push	es			; save extra segment.

	mov	ax,cs			; get base segment of cp/m.
	add	ax,tpaseg		; add offset to tpa segment.
	push	ax			; save tpa segment.
	mov	es,ax			; into extra segment.
	mov	si,0000h		; offset of 0.

fndtop:
	mov	bx,es:[si]		; save contents of memory.
	mov	ax,5555h		; get test pattern.
	mov	es:[si],ax		; write it to memory.
	cmp	es:[si],ax		; same as test pattern?
	jne	topfnd			; no, must be top of ram.

	mov	es:[si],bx		; same, res*************
	; ********************** trap entry ***********************
	; *********************************************************

	if	not loader		; start condition (loader_false).

int_trap:

	; this is a bad place to be, tell'em so and die.

	cli				; disable interrupts during service.
	mov	ax,cs
	mov	ds,ax			; get our data segment.
	mov	bx,(offset trpmsg)
	call	prtmsg			; print trap message.
	hlt				; hard stop.

	endif				; end condition (loader_false).


	; *******************it with al=00 if not ready.
	mov	dx,lptinp	; get input port address.
	in	al,dx		; read input port.
	test	al,lptdsr	; look at dsr bit.
	mov	al,0		; default is zero.
	jnz	ps_ext		; exit with zero if not ready.
	not	al		; else make it ff for ready.
ps_ext:
	pop	dx		; restore dx.
	endif

	ret			; return from printer status (flag in al).


	; printer output.

lstout:
	if	not loader
	call	pollpt		; get status.
	or	al,al		; see if ready.
	jz	lstout		; wait for ready if not.
	mov	al,cl		; get cmov	ds,ax			; data  segment.
	mov	es,ax			; extra segment.
	mov	sp,(offset stkbase)	; use local stack for ini.

	cld				; use incrementing indexes.

	xor	ax,ax
	mov	iobyte,al		; ini iobyte (tty: for consistancy).
	push	ds			; save data segment.
	mov	ds,ax			; clear data segment.

	if	not loader
	mov	es,ax			; clear extra segment.
	mov	int0_offset,(offset int_trap)	; set int 0 vector.
	mov	int0_segment,cs
	mov	di,4			; start at int 1.
	mov	si,0			; come from int 0.
	mov	cx,510			; do rest oftore memory location.
	mov	ax,es			; get segment base.
	cmp	ax,0fc00h		; last possible segment?
	jae	topfnd			; yes, stop.
	add	ax,400h			; no,  bump es by 16k.
	mov	es,ax			; set new base.
	jmps	fndtop			; loop till top of ram memory.

topfnd:
	mov	ax,es			; get last good segment.
	pop	bx			; get base of tpa segment.
	mov	tpabas,bx		; put in segtable.
	sub	ax,bx			; calculate segment length.
	sub	ax,bx			; remove cp/m offset.
	mov	memlen,ax		; put in segtable.

	pop	es			; recover extra seg**************************************
	; ****** console, printer, punch, & reader handlers *******
	; *********************************************************


	; console status check.

const:
	if	not loader
	push	dx		; save port register.
	mov	dx,consts	; get status port adr.
	in	al,dx		; read status port.
	pop	dx		; restore dx.
	and	al,conrda	; test for ready.
	jz	cs_ext		; result zero, exit test (00=not ready).
	or	al,255		; not zero, set al (ff=ready).
cs_ext:
	endif

	ret			; retuharacter from cl.
	push	dx		; save dx.
	mov	dx,lptdat	; get printer data port adr.
	out	dx,al		; print character.
	pop	dx		; restore dx.
	endif

	ret			; return from printer output.


	; punch output is same as printer output.

punch:
	jmps	lstout


	; reader input uses printer input port.

reader:
	if	not loader
	push	dx		; save dx.
	mov	dx,lptsts	; get printe