;=======================================================================
;
; XMUF.Z80 - XMODEMXX PATCH FILE FOR ECB USB-FIFO
;
;   Phil Summers - difficultylevelhigh@gmail.com
;   Updated: 2019-08-16
;
;=======================================================================
;
; Overlay file is Z80, build with M80:
;   M80 =XMHB
;   L80 XMHB,XMHB/N/X/E
;
	.Z80
	ASEG
;
NO	EQU	0
YES	EQU	NOT NO
;
ERRDET	EQU	NO		; detect parity/framing/overrun errs
;
BASE	EQU	100H		; start of cp/m normal program area
;
BDOS	EQU	00005H		; BDOS function dispatch vector
;
;=======================================================================
;
; Jump table: The jump table must be in exactly the same sequence as the
; one in XMODEM.  Note the ORG of 103H - This jump table has no jump to
; 'BEGIN'.
;
	ORG	BASE + 3	;start after 'JMP BEGIN'
;
	JP	CONOUT		;must be 00000h if not used, see below
	JP	MINIT		;initialization routine (if needed)
	JP	UNINIT		;undo whatever 'MINIT' did (or return)
JPTBL:
	JP	SENDR		;send character (via pop psw)
	JP	CAROK		;test for carrier
	JP	MDIN		;receive data byte
	JP	GETCHR		;get character from modem
	JP	RCVRDY		;check receive ready
	JP	SNDRDY		;check send ready
	JP	SPEED		;get speed value for file transfer time
	JP	EXTRA1		;extra for custom routine
	JP	EXTRA2		;extra for custom routine
	JP	EXTRA3		;extra for custom routine
;
;-----------------------------------------------------------------------
;
; Output character to console
;
CONOUT	EQU	0		; not used
;
;-----------------------------------------------------------------------
;
; Initialize modem
;
; This procedure has been usurped to dynamically detect the type
; of system we are running on and install the *real* jump table
; entries as appropriate.
;
MINIT:
;
	; Announce
	LD	DE,RBC		; RetroBrew Computers
	LD	C,9		; BDOS string display function
	CALL	BDOS		; Do it
;
	; Identify BIOS (RomWBW HBIOS or UNA UBIOS)
	CALL	IDBIO		; 1=HBIOS, 2=UBIOS
	LD	(BIOID),A	; Save it
	DEC	A		; Test for HBIOS
	JR	Z,HINIT		; Do HBIOS setup
	DEC	A		; Test for UBIOS
	JR	Z,UINIT		; Do UBIOS setup
;
	; Neither UNA nor RomWBW
	LD	DE,BIOERR	; BIOS error message
	LD	C,9		; BDOS string display function
	CALL	BDOS		; Do it
	JP	0		; Bail out!
;
HINIT:
;
	; Display RomWBW notification string
	LD	DE,HBTAG	; BIOS notification string
	LD	C,9		; BDOS string display function
	CALL	BDOS		; Do it
;
	; Get platform id from RomWBW HBIOS and save it
	LD	B,0F1H		; HBIOS VER function 0xF1
	LD	C,0		; Required reserved value
	RST	08		; Do it, L := Platform ID
	LD	A,L		; Move to A
	LD	(PLTID),A	; Save it
;
	; Get CPU speed from RomWBW HBIOS and save it
	LD	B,0F8H		; HBIOS SYSGET function 0xF8
	LD	C,0F0H		; CPUINFO subfunction 0xF0
	RST	08		; Do it, L := CPU speed in MHz
	LD	A,L		; Move it to A
	LD	(CPUSPD),A	; Save it
	JR	MINIT1		; Continue general initialization
;
UINIT:
;
	; Display UNA notification string
	LD	DE,UBTAG	; BIOS notification string
	LD	C,9		; BDOS string display function
	CALL	BDOS		; Do it
;
	; Get CPU speed from UNA and save it
	LD	C,0F8H		; UNA BIOS Get PHI function
	RST	08		; Returns speed in Hz in DE:HL
	LD	B,4		; Divide MHz in DE:HL by 100000H 
UINIT1:
	SRL	D		; ... to get approx CPU speed in
	RR	E		; ...MHz.  Throw away HL, and
	DJNZ	UINIT1		; ...right shift DE by 4.
	INC	E		; Fix up for value truncation
	LD	A,E		; Put in A
	LD	(CPUSPD),A	; Save it
	JR	MINIT1		; Continue general initialization
;
MINIT1:
	LD	HL,1250		; Smaller receive loop timeout scalar
	LD	(RCVSCL),HL	; ... to compensate for BIOS overhead
	LD	HL,UF_JPTBL	; HBIOS jump table address
	LD	DE,USB_FIFO	; HBIOS console notification string
	JR	MINIT3		; Complete the initialization
;
MINIT3:
	PUSH	HL		; Save HL

	; Display port notification string
	LD	C,9		; BDOS string display function
	CALL	BDOS		; Do it
;
	; Newline
	LD	C,9		; BDOS string display function
	LD	DE,CRLF		; Newline
	CALL	BDOS		; Do it
;
	; Copy real vectors into active jump table
	POP	HL		; Recover HL
	LD	DE,JPTBL	; Real jump table is destination
	LD	BC,7 * 3	; Copy 7 3-byte entries
	LDIR			; Do the copy
;
	; Return with CPU speed in A
	LD	A,(CPUSPD)	; A := CPU speed in MHz
	LD	HL,(RCVSCL)	; HL := receive scalar

	RET			; and return
;
; Identify active BIOS.  RomWBW HBIOS=1, UNA UBIOS=2, else 0
;
IDBIO:
;
	; Check for UNA (UBIOS)
	LD	A,(0FFFDH)	; fixed location of UNA API vector
	CP	0C3H		; jp instruction?
	JR	NZ,IDBIO1	; if not, not UNA
	LD	HL,(0FFFEH)	; get jp address
	LD	A,(HL)		; get byte at target address
	CP	0FDH		; first byte of UNA push ix instruction
	JR	NZ,IDBIO1	; if not, not UNA
	INC	HL		; point to next byte
	LD	A,(HL)		; get next byte
	CP	0E5H		; second byte of UNA push ix instruction
	JR	NZ,IDBIO1	; if not, not UNA, check others
	LD	A,2		; UNA BIOS id = 2
	RET			; and done
;
IDBIO1:
	; Check for RomWBW (HBIOS)
	LD	HL,(0FFFCH)	; HL := HBIOS ident location
	LD	A,'W'		; First byte of ident
	CP	(HL)		; Compare
	JR	NZ,IDBIO2	; Not HBIOS
	INC	HL		; Next byte of ident
	LD	A,~'W'		; Second byte of ident
	CP	(HL)		; Compare
	JR	NZ,IDBIO2	; Not HBIOS
	LD	A,1		; HBIOS BIOS id = 1
	RET			; and done
;
IDBIO2:
	; No idea what this is
	XOR	A		; Setup return value of 0
	RET			; and done
;
;
;
BIOID	DB	0		; BIOS ID, 1=HBIOS, 2=UBIOS
PLTID	DB	0		; Platform ID
CPUSPD	DB	10		; CPU speed in MHz
RCVSCL	DW	2800		; RECV loop timeout scalar
;
RBC	DB	"RBC, 16-Aug-2018$"
;
USB_FIFO	DB	", USB-FIFO$"
;
UBTAG	DB	" [UNA]$"
HBTAG	DB	" [WBW]$"
;
CRLF	DB	13, 10, "$"
;
BIOERR	DB	13, 10, 13, 10, "++ Unknown BIOS ++", 13, 10, "$"
;
;-----------------------------------------------------------------------
;
; Uninitialize modem
;
UNINIT:
	LD	A,(BIOID)
	CP	1		; Is HBIOS?
	RET	NZ		; If not, just return
	
	; Reset character device 0
	LD	B,04H		; HBIOS CIOINIT function 0x04
	LD	C,0		; Unit = 0
	LD	DE,-1		; Reset w/ current settings
	RST	08		; Do it
	RET			; not initialized, so no 'UN-INITIALIZE'
;
;-----------------------------------------------------------------------
;
; The following are all dummy routines that are unused because MINIT
; dynamically installs the real jump table.
;
SENDR:
CAROK:
MDIN:
GETCHR:
RCVRDY:
SNDRDY:
SPEED:
EXTRA1:
EXTRA2:
EXTRA3:
	RET
;
;=======================================================================
;=======================================================================
;
; WILL SOWERBUTTS ECB USB-FIFO 
;
;=======================================================================
;=======================================================================
;
FIFO_BASE	EQU	0CH
FIFO_DATA       EQU	(FIFO_BASE+0)
FIFO_STATUS     EQU	(FIFO_BASE+1)
FIFO_SEND_IMM   EQU	(FIFO_BASE+2)
;
; Following jump table is dynamically patched over initial jump
; table at program startup.  See MINIT above.  Note that only a
; subset of the jump table is overlaid (SENDR to SPEED).
;
UF_JPTBL:
	JP	UF_SENDR		;send character (via pop psw)
	JP	UF_CAROK		;test for carrier
	JP	UF_MDIN			;receive data byte
	JP	UF_GETCHR		;get character from modem
	JP	UF_RCVRDY		;check receive ready
	JP	UF_SNDRDY		;check send ready
	JP	UF_SPEED		;get speed value for file transfer time
;
;-----------------------------------------------------------------------
;
; Send character on top of stack
;
UF_SENDR:

	POP	AF			; get character to send from stack
	OUT	(FIFO_DATA),A		; WRITE TO FIFO
	OUT	(FIFO_SEND_IMM),A	; SEND IMMEDIATE
	RET
;
;-----------------------------------------------------------------------
;
; Test and report carrier status, Z set if carrier present
;
UF_CAROK:
	XOR	A			; not used, always indicate present
	RET
;
;-----------------------------------------------------------------------
;
; Get a character (assume character ready has already been tested)
;
; This routine must NOT block.
;
UF_MDIN:
UF_GETCHR:
	IN	A,(FIFO_DATA)		; GET CHAR
	RET
;
;-----------------------------------------------------------------------
;
; Test for character ready to receive, Z = ready
; Error code returned in A register
; *** Error code does not seem to be used ***
;
UF_RCVRDY:
	IN	A,(FIFO_STATUS)		; B7=0 IF CHAR AVAIL, =1 IF NO CHAR.
	RLCA				; B0=0 IF CHAR AVAIL, =1 IF NO CHAR.
	AND	00000001B		; A=0, ZF=1 IF NO CHAR, A=1, ZF=0 IF CHAR AVAIL, 
	LD	A,0
	RET
;
;-----------------------------------------------------------------------
;
; Test for ready to send a character, Z = ready
;
UF_SNDRDY:
	IN	A,(FIFO_STATUS)		; Bit 0=0 IF SPACE AVAIL, =1 IF FULL
	AND	00000001B		; A=0, ZF=1 IF SPACE AVAIL, A=1, ZF=0 IF FULL.
	RET
;
;-----------------------------------------------------------------------
;
; Report baud rate (index into SPTBL returned in register A)
;
UF_SPEED:
	LD	A,8			; arbitrarily return 9600 baud
	RET
;
	END