prn.z80

; ---------------
; 4x8 font driver, (c) 2007 Andrew Owen
; ---------------

;	org	50000		;  In the original this was fixed.

; --------------------------------
; CREATE CHANNEL AND ATTACH STREAM
; --------------------------------
;
; Based on code by Ian Beardsmore from Your Spectrum issue 7, September 1984.

c_chan:	ld	hl,($5c53)	; a channel must be created below basic
				; so look at the system variable PROG
	dec	hl		; move hl down one address

	ld	bc,$0005	; the new channel takes 5 bytes
	call	$1655		; call the MAKE_ROOM routine
	inc	hl		; move HL up one address

	ld	bc,chan_4	; could write the bytes directly but
				; then code would be non-relocatable

	ld	(hl),c		; low byte of the output routine
	inc	hl		; move HL up one address
	push	hl		; save this address for later

	ld	(hl),b		; high byte of the output routine
	inc	hl		; move HL up one address

	ld	bc,$15c4	; address of input routine

	ld	(hl),c		; low byte of the input routine
	inc	hl		; move HL up one address

	ld	(hl),b		; high byte of the input routine
	inc	hl		; move HL up one address

	ld	(hl),'P'	; channel type; 'K', 'S', 'R' or 'P'

; attach stream

	pop	hl		; the first address plus one of the
				; extra space stored earlier
	ld	de,($5c4f)	; store the contents of CHANS in DE
	and	a		; clear the carry flag before
				; calculation
	sbc	hl,de		; the difference between the start of
				; the channels area and the start of the
				; extra space becomes the offset, stored
				; in HL
	ex	de,hl		; store the offset in DE

	ld	hl,$5c10	; store the contents of STRMS in HL
	ld	a,$04		; stream number 4
	add	a,$03		; take account of streams -3 to -1
	add	a,a		; each of the seven default streams has
				; two bytes of offset data
				; the total number of bytes occupied,
				; held in a, forms the offset for the
				; new stream
	ld	b,$00		; set b to hold $00
	ld	c,a		; set the low byte of the offset
	add	hl,bc		; the offset is added to the base
				; address to give the correct location
				; in the streams table to store the
				; offset
	ld	(hl),e		; the low byte of the offset
	inc	hl		; move HL up one address
	ld	(hl),d		; the high byte of the offset
	ret			; all done

; -----------------
; CHANNEL #4 OUTPUT
; -----------------
;
; Based on code by Tony Samuels from Your Spectrum issue 13, April 1985.
; A channel wrapper for the 64-column display driver.

chan_4:	ld	b,a		; save character
	ld	a,(atflg)	; value of AT flag
	and	a		; test against zero
	jr	nz,getrow	; jump if not
	ld	a,b		; restore character

atchk:	cp	$16		; test for AT
	jr	nz,crchk	; if not test for CR
	ld	a,$ff		; set the AT flag
	ld	(atflg),a	; next character will be row
	ret			; return

getrow:	cp	$fe		; test AT flag
	jr	z,getcol	; jump if setting col
	ld	a,b		; restore character
	cp	$18		; greater than 23?
	jr	nc,err_b	; error if so

	ld	(row),a		; store it in row
	ld	hl,atflg	; AT flag
	dec	(hl)		; indicates next character is col
	ret			; return

getcol:	ld	a,b		; restore character
	cp	$40		; greater than 63?
	jr	nc,err_b	; error if so
	ld	(col),a		; store it in col
	xor	a		; set a to zero
	ld	(atflg),a	; store in AT flag
	ret			; return

err_b:	xor	a		; set a to zero
	ld	(atflg),a	; clear AT flag
	rst	08h		;
	defb	$0a		;

crchk:	cp	$0d		; check for return
	jr	z,do_cr		; to carriage return if so
	call	pr_64		; print it

	ld	hl,col		; increment
	inc	(hl)		; the column
	ld	a,(hl)		;

	cp	$40		; column 64?
	ret	nz		;

do_cr:	xor	a		; set A to zero
	ld	(col),a		; reset column
	ld	a,(row)		; get the row
	inc	a		; increment it
	cp	$18		; row 24?
	jr	z,wrap		;

zend:	ld	(row),a		; write it back
	ret

wrap:	xor	a		;
	jr	zend		;

; ------------------------
; 64 COLUMN DISPLAY DRIVER
; ------------------------

pr_64:	rra			; divide by two with remainder in carry flag

	ld	h,$00		; clear H
	ld	l,a		; CHAR to low byte of HL

	ex	af,af'		; save the carry flag

	add	hl,hl		; multiply
	add	hl,hl		; by
	add	hl,hl		; eight
	ld	de,font-$80	; offset to FONT
	add	hl,de		; HL holds address of first byte of
				; character map in FONT
	push	hl		; save font address

; convert the row to the base screen address

	ld	a,(row)		; get the row
	ld	b,a		; save it
	and	$18		; mask off bit 3-4
	ld	d,a		; store high byte of offset in D
	ld	a,b		; retrieve it
	and	$07		; mask off bit 0-2
	rlca			; shift
	rlca			; five
	rlca			; bits
	rlca			; to the
	rlca			; left
	ld	e,a		; store low byte of offset in E

; add the column

	ld	a,(col)		; get the column
	rra			; divide by two with remainder in carry flag
	push	af		; store the carry flag

	ld	h,$40		; base location
	ld	l,a		; plus column offset

	add	hl,de		; add the offset

	ex	de,hl		; put the result back in DE

; HL now points to the location of the first byte of char data in FONT_1
; DE points to the first screen byte in SCREEN_1
; C holds the offset to the routine

	pop	af		; restore column carry flag
	pop	hl		; restore the font address

	jr	nc,odd_col	; jump if odd column

even_col:
	ex	af,af'		; restore char position carry flag
	jr	c,l_on_l	; left char on left col
	jr	r_on_l		; right char on left col

odd_col:
	ex	af,af'		; restore char position carry flag
	jr	nc,r_on_r	; right char on right col
	jr	l_on_r		; left char on right col

; -------------------------------
; WRITE A CHARACTER TO THE SCREEN
; -------------------------------
;
; There are four separate routines

; HL points to the first byte of a character in FONT
; DE points to the first byte of the screen address

; left nibble on left hand side

l_on_l:	ld	c,$08		; 8 bytes to write
ll_lp:	ld	a,(de)		; read byte at destination
	and	$f0		; mask area used by new character
	ld	b,a		; store in b
	ld	a,(hl)		; get byte of font
	and	$0f		; mask off unused half
	or	b		; combine with background
	ld	(de),a		; write it back
	inc	d		; point to next screen location
	inc	hl		; point to next font data
	dec	c		; adjust counter
	jr	nz,ll_lp	; loop 8 times
	ret			; done

; right nibble on right hand side

r_on_r:	ld	c,$08		; 8 bytes to write
rr_lp:	ld	a,(de)		; read byte at destination
	and	$0f		; mask area used by new character
	ld	b,a		; store in b
	ld	a,(hl)		; get byte of font
	and	$f0		; mask off unused half
	or	b		; combine with background
	ld	(de),a		; write it back
	inc	d		; point to next screen location
	inc	hl		; point to next font data
	dec	c		; adjust counter
	jr	nz,rr_lp	; loop 8 times
	ret			; done

; left nibble on right hand side

l_on_r:	ld	c,$08		; 8 bytes to write
lr_lp:	ld	a,(de)		; read byte at destination
	and	$0f		; mask area used by new character
	ld	b,a		; store in b
	ld	a,(hl)		; get byte of font
	rrca			; shift right
	rrca			; four bits
	rrca			; leaving 7-4
	rrca			; empty
	and	$f0		;
	or	b		; combine with background
	ld	(de),a		; write it back
	inc	d		; point to next screen location
	inc	hl		; point to next font data
	dec	c		; adjust counter
	jr	nz,lr_lp	; loop 8 times
	ret			; done

; right nibble on left hand side

r_on_l:	ld	c,$08		; 8 bytes to write
rl_lp:	ld	a,(de)		; read byte at destination
	and	$f0		; mask area used by new character
	ld	b,a		; store in b
	ld	a,(hl)		; get byte of font
	rlca			; shift left
	rlca			; four bits
	rlca			; leaving 3-0
	rlca			; empty
	and	$0f		;
	or	b		; combine with background
	ld	(de),a		; write it back
	inc	d		; point to next screen location
	inc	hl		; point to next font data
	dec	c		; adjust counter
	jr	nz,rl_lp	; loop 8 times
	ret			; done

; --------------
; TEXT VARIABLES
; --------------
;
; Used by the 64 column driver

atflg:	defb	$00		; AT flag
row:	defb	$00		; row
col:	defb	$00		; col

; -------------------
; half width 4x8 font
; -------------------
;
; 384 bytes

font:
	defb	$00,$02,$02,$02,$02,$00,$02,$00,$00,$52,$57,$02,$02,$07,$02,$00;
	defb	$00,$25,$71,$62,$32,$74,$25,$00,$00,$22,$42,$30,$50,$50,$30,$00;
	defb	$00,$14,$22,$41,$41,$41,$22,$14,$00,$20,$70,$22,$57,$02,$00,$00;
	defb	$00,$00,$00,$00,$07,$00,$20,$20,$00,$01,$01,$02,$02,$04,$14,$00;
	defb	$00,$22,$56,$52,$52,$52,$27,$00,$00,$27,$51,$12,$21,$45,$72,$00;
	defb	$00,$57,$54,$56,$71,$15,$12,$00,$00,$17,$21,$61,$52,$52,$22,$00;
	defb	$00,$22,$55,$25,$53,$52,$24,$00,$00,$00,$00,$22,$00,$00,$22,$02;
	defb	$00,$00,$10,$27,$40,$27,$10,$00,$00,$02,$45,$21,$12,$20,$42,$00;
	defb	$00,$23,$55,$75,$77,$45,$35,$00,$00,$63,$54,$64,$54,$54,$63,$00;
	defb	$00,$67,$54,$56,$54,$54,$67,$00,$00,$73,$44,$64,$45,$45,$43,$00;
	defb	$00,$57,$52,$72,$52,$52,$57,$00,$00,$35,$15,$16,$55,$55,$25,$00;
	defb	$00,$45,$47,$45,$45,$45,$75,$00,$00,$62,$55,$55,$55,$55,$52,$00;
	defb	$00,$62,$55,$55,$65,$45,$43,$00,$00,$63,$54,$52,$61,$55,$52,$00;
	defb	$00,$75,$25,$25,$25,$25,$22,$00,$00,$55,$55,$55,$55,$27,$25,$00;
	defb	$00,$55,$55,$25,$22,$52,$52,$00,$00,$73,$12,$22,$22,$42,$72,$03;
	defb	$00,$46,$42,$22,$22,$12,$12,$06,$00,$20,$50,$00,$00,$00,$00,$0F;
	defb	$00,$20,$10,$03,$05,$05,$03,$00,$00,$40,$40,$63,$54,$54,$63,$00;
	defb	$00,$10,$10,$32,$55,$56,$33,$00,$00,$10,$20,$73,$25,$25,$43,$06;
	defb	$00,$42,$40,$66,$52,$52,$57,$00,$00,$14,$04,$35,$16,$15,$55,$20;
	defb	$00,$60,$20,$25,$27,$25,$75,$00,$00,$00,$00,$62,$55,$55,$52,$00;
	defb	$00,$00,$00,$63,$55,$55,$63,$41,$00,$00,$00,$53,$66,$43,$46,$00;
	defb	$00,$00,$20,$75,$25,$25,$12,$00,$00,$00,$00,$55,$55,$27,$25,$00;
	defb	$00,$00,$00,$55,$25,$25,$53,$06,$00,$01,$02,$72,$34,$62,$72,$01;
	defb	$00,$24,$22,$22,$21,$22,$22,$04,$00,$56,$A9,$06,$04,$06,$09,$06;