;
;==================================================================================================
; PLD-USB SERIAL DRIVER
;==================================================================================================
;
; THIS SERIAL DRIVER SUPPORTS THE DLP-USB DEVICE ON THE S100 SERIAL-IO
; BOARD.  THE STATUS PORT IS ACTUALLY BITS 6-7 OF PORT C OF THE 8255.
;
; STATUS BITS:				IDLE
;   7: 0=CHAR PENDING			1
;   6: 0=XMIT HOLDING REGISTER EMPTY	0
;   5-0: UNDEFINED
;
; TODO:
;
PLDSER_PPI_BASE	.EQU	$A8
;
PLDSER_PPIA	.EQU	PLDSER_PPI_BASE + 0
PLDSER_PPIB	.EQU	PLDSER_PPI_BASE + 1
PLDSER_PPIC	.EQU	PLDSER_PPI_BASE + 2
PLDSER_PPICTL	.EQU	PLDSER_PPI_BASE + 3
;
PLDSER_STAT	.EQU	PLDSER_PPIC
PLDSER_DATA	.EQU	PLDSER_PPI_BASE + 4
;
; ACCORDING TO THE S100 SERIAL-IO BOARD CONVENTIONS, THE PPI IS
; CONFIGURED FOR MODE 0 WITH A=INPUT, B=OUTPUT, C0-3=OUTPUT,
; C4-7=INPUT
;
PLDSER_PPICFG	.EQU	%10011000
;
		DEVECHO	"PLDSER: IO="
		DEVECHO	PLDSER_DATA
		DEVECHO	"\n"
;
;
;
PLDSER_PREINIT:
;
; TEST FOR PRESENCE
;
	XOR	A			; CLEAR ACCUM
	LD	(PLDSER_PRESENT),A	; PRESET TO NOT PRESENT
	CALL	PLDSER_DETECT		; CHECK FOR HARDWARE, Z=PRESENT
	RET	NZ			; ABORT IF NOT PRESENT
	OR	$FF			; PRESENT FLAG
	LD	(PLDSER_PRESENT),A	; STORE IT
;
	CALL	PLDSER_INITDEV
;
; ADD OURSELVES TO CIO DISPATCH TABLE
;
	LD	D,0			; PHYSICAL UNIT IS ZERO
	LD	E,CIODEV_PLDSER		; DEVICE TYPE
	LD	BC,PLDSER_FNTBL		; BC := FUNCTION TABLE ADDRESS
	CALL	CIO_ADDENT		; ADD ENTRY, A := UNIT ASSIGNED
;
	XOR	A
	RET
;
;
;
PLDSER_INIT:
	LD	A,(PLDSER_PRESENT)	; PRESENT FLAG
	OR	A			; SET FLAGS
	RET	Z			; ABORT IF NOT PRESENT
	CALL	NEWLINE
	PRTS("PLDSER:$")
	PRTS(" IO=0x$")			; FORMATTING
	LD	A,PLDSER_DATA
	CALL	PRTHEXBYTE
;
	XOR	A			; SIGNAL SUCCESS
	RET
;
; DRIVER FUNCTION TABLE
;
PLDSER_FNTBL:
	.DW	PLDSER_IN
	.DW	PLDSER_OUT
	.DW	PLDSER_IST
	.DW	PLDSER_OST
	.DW	PLDSER_INITDEV
	.DW	PLDSER_QUERY
	.DW	PLDSER_DEVICE
#IF (($ - PLDSER_FNTBL) != (CIO_FNCNT * 2))
	.ECHO	"*** INVALID PLDSER FUNCTION TABLE ***\n"
#ENDIF
;
;
;
PLDSER_IN:
	CALL	PLDSER_IST		; CHECK FOR CHAR PENDING
	JR	Z,PLDSER_IN		; WAIT FOR IT IF NECESSARY
	IN	A,(PLDSER_DATA)		; READ THE CHAR
	LD	E,A
	RET
;
;
;
PLDSER_IST:
	IN	A,(PLDSER_STAT)		; READ LINE STATUS REGISTER
	CPL
	AND	%10000000		; ISOLATE DATA READY
	JP	Z,CIO_IDLE		; RETURN VIA IDLE PROCESSING
	OR	$FF			; SET A=$FF TO SIGNAL READY
	RET				; RETURN
;
;
;
PLDSER_OUT:
	CALL	PLDSER_OST		; CHECK FOR OUTPUT READY
	JR	Z,PLDSER_OUT		; WAIT IF NECESSARY
	LD	A,E			; RECOVER THE CHAR TO WRITE
	OUT	(PLDSER_DATA),A		; WRITE THE CHAR
	RET
;
;
;
PLDSER_OST:
	IN	A,(PLDSER_STAT)		; READ LINE STATUS REGISTER
	CPL
	AND	%01000000 		; ISOLATE OUTPUT RDY
	JP	Z,CIO_IDLE		; RETURN VIA IDLE PROCESSING
	OR	$FF			; SET A=$FF TO SIGNAL READY
	RET				; RETURN
;
;
;
PLDSER_INITDEV:
	; INIT THE PPI.  THE PLD ADAPTER ITSELF HAS NO
	; CONFIGURATION CAPABILITIES.
	LD	A,PLDSER_PPICFG		; CONFIG 8255 PORTS: B=OUTPUT
	OUT	(PLDSER_PPICTL),A	; WRITE CONTROL WORD
	RET
;
;
;
PLDSER_QUERY:
	LD	DE,PLDSERCFG
	XOR	A
	RET
;
;
;
PLDSER_DEVICE:
	LD	D,CIODEV_PLDSER		; D := DEVICE TYPE
	LD	E,0			; E := DEVICE NUM, ALWAYS 0
	LD	C,$00			; C := DEVICE TYPE, 0x00 IS RS-232
	LD	H,0			; H := 0, DRIVER HAS NO MODES
	LD	L,PLDSER_DATA		; L := BASE I/O ADDRESS
	XOR	A			; SIGNAL SUCCESS
	RET
;
; TEST FOR HARDWARE PRESENCE.  THE PLD ADAPTER STATUS IS EXPOSED THROUGH
; AN 8255 PPI.  DETECTING THE PLD ITSELF IS BASICALLY IMPOSSIBLE GIVEN
; THERE ARE ONLY TWO STATUS BITS WITH VALUES THAT SHOULD NOT BE ASSUMED.
; SO, HERE WE JSUT CHECK FOR THE EXISTENCE OF THE PPI ITSELF WHICH IS
; USED TO INFER THE EXCISTENCE OF THE PLD ADAPTER.
;
PLDSER_DETECT:
;
	; WE SETUP THE PPI TO WRITE, THEN WRITE A TEST VALUE
	; TO PORT B, THEN READ IT BACK.  IF THE PPI IS THERE
	; THEN THE BUS HOLD CIRCUITRY WILL READ BACK THE TEST VALUE.
	LD	A,PLDSER_PPICFG		; CONFIG 8255 PORTS: B=OUTPUT
	OUT	(PLDSER_PPICTL),A	; WRITE CONTROL WORD
	LD	A,$A5			; TEST VALUE
	OUT	(PLDSER_PPIB),A		; WRITE IT
	IN	A,(PLDSER_PPIB)		; READ IT
	CP	$A5
	RET
;
;
;
PLDSER_PRESENT	.DB	0		; FLAG FOR HARDWARE PRESENT