SBTTL 'IRQ Handelers and I/O Routines (12_Dec_84)'
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;======================================================================
;
;	Copyright 1984
;	Morrow Designs, Inc.
;	San Leandro, Ca.
;
;
; Module Description:
;--------------------
;		This module contains the interrupt routines, the circular
;	buffer handeling routines and the keyboard input and output routines.
;
;----------------------------------------------------------------------
; Index (12_Nov_84)
;------------------
;
;	IRQVEC	Maskable Interrupt Entry
;	NMIVEC	Non_Maskable Interrupt Entry
;
;	SNDINS	Insert a Character into the Send Buffer
;	SNDREM	Remove a Character from the Send Buffer
;	ININS	Insert a Character into the Input Buffer
;	INREM	Remove a Character from the Input Buffer
;	KEYINS	Insert a Character into the Key Buffer
;	KEYREM	Remove a Character from the Key Buffer
;
;	GETKEY	Get a Character from the Keyboard
;	PUTKEY	Put a Character to the Keyboard
	PAGE

;----------------------------------------------------------------------
; Maskable Interrupt Entry Point (12_Dec_84)
;-------------------------------------------
;	1) Irq occurs when the keyboard wants to send a char to the processor
;	2) The FTCHKEY entry is only used by the PUTKEY routine.
;
	;PUTKEY Entry Point
FTCHKEY:PLA			;Alias an IRQ (so RTI returns properly)
	TAX
	INX
	TXA
	PHA			;increment the return address by one
	PHP			;push the status onto the stack

	;Normal IRQ Entry Point
IRQVEC:	PHA			;Save the Registers
	TYA
	PHA
	TXA
	PHA
	JSR	GETKEY		;Get the key from the keyboard

	LDY	LOCKMD		;If (Keyboard ne Locked)
	BMI	IRQSK1

	JSR	KEYINS		;	Insert Character into the Key Buffer
IRQSK1:	PLA
	TAX			;Restore the Registers
	PLA
	TAY
	PLA
	RTI			;Return
	PAGE

;----------------------------------------------------------------------
; Non_Maskable Interrupt Entry Point (12_Dec_84)
;-----------------------------------------------
;	1) This Routine handels interrupts from the UART (ie the host computer
;	   has sent a character). Control is transfer to this routine from the
;	   page zero vector (see the DATxx module and the PUTKEY routines).
;	2) The GETNMI entry is only used by the PUTKEY routine.
;	3) Notice that nulls are ignored unless we're in monitor mode.
;
	;PUTKEY Entry Point
GETNMI:	PLA			;Alias an IRQ (so RTI returns properly)
	TAX
	INX
	TXA
	PHA			;increment the return address by one
	PHP			;push the status onto the stack

	;Normal NMI Entry Point
NMIVEC:	SEI			;disable maskable interrupts
	PHA
	TYA			;(Save the Index Registers)
	PHA
	TXA
	PHA
	LDA	S1DATA		;Get a Character from the Uart
	AND	#%01111111	;(Remove the Parity Bit)
	BNE	NMISK1		;If ( (Char ne 0) Or

	LDY	MONITOR		;     (Monitor eq Enabled) )
	BEQ	NMISK2

NMISK1:	JSR	ININS		;	Insert Char into Input Buffer
NMISK2:	PLA			;Restore the Registers
	TAX
	PLA
	TAY
	PLA
	RTI			;Return
	PAGE

;----------------------------------------------------------------------
; Insert a Character into the Send Buffer (30_Nov_84)
;----------------------------------------------------
;
SNDINS:	LDY	BRKHIT		;If (BrkHit eq True)
	BEQ	SISK1

	CMP	#CTRLC		;	If (Character to Store eq ^C)
	BEQ	SISK2		;		return

	LDY	#0		;	Else
	STY	BRKHIT		;		BRKHIT = FALSE

SISK1:	LDY	OUTEP		;Y:= End Buffer Index
	INY			;Increment the End Buffer Index
	CPY	OUTSP		;If (The Buffer HAS NOT Overrun)
	BEQ	SISK2

	STY	OUTEP		;	Save the End Buffer Offset
	STA	SNDBUF,Y	;	Store the Character
SISK2:	RTS			;Return

;----------------------------------------------------------------------
; Remove a Character from the Send Buffer (30_Nov_84)
;----------------------------------------------------
;
SNDREM:	LDX	OUTSP		;X:= Start Buffer Index
	CPX	OUTEP
	BNE	SRSK1		;If (The Buffer is Empty)

	LDA	#$FF		;	A:= 0FF (Buffer Empty Flag)
	RTS			;	Return

SRSK1:	INX			;Else	Increment the Start Buffer Index
	STX	OUTSP		;	Update the Start Buffer Index
	LDA	SNDBUF,X	;	A:= Next Character
	RTS			;	Return
	PAGE

;----------------------------------------------------------------------
; Insert a Character into the Input Buffer (28_Nov_84)
;-----------------------------------------------------
;
ININS:	TAX			;(save the character)
	LDY	#0		;Y_Index:= 0
	LDA	#$FF
	CMP	(INEP),Y	;If (Buffer is NOT Full)
	BNE	IISK2

	TXA			;	(restore character)
	STA	(INEP),Y	;	Put the Character in the Buffer
	INC	INEP		;	Increment the Storage Pointer
	BNE	IISK1

	INC	INEP+1
	LDA	INEP+1
	AND	#7		;	(Last Location in Buffer is $7FF)
	ORA	#HIGH INBUF	;	(First Location in Buffer is $400)
	STA	INEP+1
IISK1:	RTS			;	Return

IISK2:	STA	BUFFULL		;Else	Set the Buffer Full Flag
	RTS			;	Return

;----------------------------------------------------------------------
; Remove a Character from the Input Buffer (28_Nov_84)
;-----------------------------------------------------
;
INREM:	LDY	#0		;Y_Index:= 0
	LDA	(INSP),Y	;A:= Character from inbuf
	CMP	#$FF		;If (There is a valid Character in the Buffer)
	BEQ	IRSK2

	TAX			;	(save the character removed)
	LDA	#$FF
	STA	(INSP),Y	;	mark the spot empty
	INC	INSP
	BNE	IRSK1		;	Adjust the Buffer Pointer

	INC	INSP+1
	LDA	INSP+1
	AND	#7		;	(Last Location in Buffer is $7FF)
	ORA	#HIGH INBUF	;	(First Location in Buffer is $400)
	STA	INSP+1

IRSK1:	TXA			;(get char back)
IRSK2:	RTS			;Return
	PAGE

;----------------------------------------------------------------------
; Insert a Character into the Key Buffer (26_Nov_84)
;---------------------------------------------------
;
KEYINS:	TAY			;Y:= Character to Store
	LDX	KEYSP		;X:= Key Start Index
	TXA			;A:= Key Start Index
	CLC
	ADC	#1		;Increment the Start Pointer
	AND	#$1F		;(Truncate Pointer to 32 Locations)
	CMP	KEYEP		;If (Incremented Start Pointer ne End Pointer)
	BEQ	KISK1

	STA	KEYSP		;	Update the Key Start Pointer
	STY	KEYBUF,X	;	Put character in the Keyboard Buffer
KISK1:	RTS			;Return

;----------------------------------------------------------------------
; Remove a Character from the Key Buffer (21_Nov_84)
;---------------------------------------------------
;
KEYREM:	LDX	KEYEP		;X:= Key End Index
	LDY	KEYBUF,X	;Y:= Character from Keyboard Buffer
	INX
	TXA			;A:= Key End Index + 1
	AND	#$1F		;(Truncate Index to 32 Locations)
	STA	KEYEP		;Update the Key End Pointer
	TYA			;A:= Character read from the Buffer
	RTS			;Return
	PAGE

;----------------------------------------------------------------------
; Get a Character from the Keyboard
;----------------------------------
;	1) returns with character in A reg
;
GETKEY:	LDX	#0
	STX	PARTIAL		; clear input assembly area
	LDX	#3
	JSR	KDLY		; wait 30 micro seconds
	LDY	#8		; set to receive 8 data bits from kbrd

GTKLP1:	LDA	#1	
	ORA	BDREG		; must not change other bits in baud register
	STA	BAUD		; send request data to KBRD
	LDX	#21
	JSR	KDLY		; wait 210 microseconds
	LDA	BAUD
	AND	#%10000000	; get kbrd data bit
	ORA	PARTIAL		; add in other bits
	STA	PARTIAL		; save the bit(s) we have so far	
	LDA	BDREG
	STA	BAUD		; clear request data
	DEY
	BEQ	GTKSK1		; if 0, then we have 8 bits, so go

	LDA	PARTIAL		; else, set up partial for getting next bit added to it
	LSR	A
	STA	PARTIAL		; and restore partial
	LDX	#10
	JSR	KDLY		; wait 100 micro secs
	JMP	GTKLP1		; then, go get the next bit

GTKSK1:	LDX	 #10
	JSR	KDLY
	LDA	PARTIAL		; get the character we rcv'd
	RTS
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;----------------------------------------------------------------------
; Put a Character to the Keyboard (12_Dec_84)
;--------------------------------------------
;	1) This routine sends the character in A reg to the keyboard.
;	2) If the last character sent was a bell then a delay is inserted
;	   before sending the character to give the keyboard time to transmit
;	   a character.
;	3) Notice that the NMI vector in page zero is redirected during
;	   the contention check to a routine (in page zero) that increments
;	   the Y register and then returns; Consequently, after the contention
;	   check, if the Y register is non-zero then there is a character from
;	   the host that needs to be processed.
;
	;Check for a Bell Delay
PUTKEY:	LDX	BELSNT		;If (Last Character Sent was a Bell)
	BEQ	PTKSK1

	LDY	#40		;	Y:= Number of 2560 us delays (.1 sec)
PTKLP0:	LDX	#$FF		;	Repeat	X:= 2560 us Delay
	JSR	KDLY		;		Delay 2560 us
	DEY			;		Decrement Delay Count
	BNE	PTKLP0		;	Until (Number of 2560 us Delays eq 0)

PTKSK1:	LDX	#0		;Set Bell Flag to False (Zero)
	CMP	#BEEP		;If (Current Character is a Bell)
	BNE	PTKSK2
	DEX			;	Set Bell Flag to True (Non_Zero)

PTKSK2:	STX	BELSNT		;Update the Bell Sent Flag
	SEI			;Disable Interrupts
	PHA			;(Save Char to Send)

	;Quick Contention Check
PTKLP1:	LDX	BAUD		;While (Keyboard is trying to Send)
	BPL	PTKSK3

PTKLP2:	JSR	FTCHKEY		;	handle KBRD request as an interrupt
	JMP	PTKLP1

PTKSK3:	LDX	#4		;Counter:= 10us delay
PTKLP3:	DEX			;Repeat Decrement the Counter
	BNE	PTKLP3		;Until (Counter eq 0)

	;Request Attention
	LDA	#$1		;assert attention to KBRD
	ORA	BDREG		;but without affecting other bits
	STA	BAUD

	;Full Contention Check
	LDY	#0		;Y:= Host Request Flag
	LDX	#4		;X:= Timer
	LDA	#LOW NMICNT
	STA	VCTNMI+1	;Redirect the NMI Vector

	LDX	#2		;Counter:= 5us delay
PTKLP4:	DEX			;Repeat Decrement the Counter
	BNE	PTKLP4		;Until (Counter eq 0)

	LDX	#4
	LDA	#LOW NMINRM
	STA	VCTNMI+1	;Restore the Normal NMI Vector

	LDX	BAUD		;check if KBRD Ack asserted
	BPL	PTKSK4		;If ( keyboard Ack asserted) then

	LDA	BDREG
	STA	BAUD		;	cancel request to keyboard,
	DEY			;	If (There was an NMI)
	BNE	PTKLP2

	JSR	GETNMI		;		Get the Key from the Host
	JMP	PTKLP2		;	GoTo get the char from the keyboard

	;Begin Transfer
PTKSK4:	DEY			;If (there was an NMI)
	BNE	PTKSK5

	JSR	GETNMI		;	Get the Key from the Host
PTKSK5:	LDY	#8		;Y:= Bit Counter (set to send 8 data bits)

ACK1:	LDX	BAUD		;Repeat	wait for KBRD to request data
	BPL	ACK1

	PLA			;	get char to send
	TAX			;	save it
	LSR	A		;	shift it for next time through
	PHA			;	put back on stack
	TXA			;	get bit to send
	AND	#1		;	only LSB is needed
	ORA	BDREG		;	be sure not to change rest of register
	STA	BAUD		;	output bit to KBRD

PTKLP5:	LDX	BAUD		;	wait for KBRD to ACK that it got bit
	BMI	PTKLP5

	DEY			;	now, adjust number of bits left to send
	BNE	ACK1		;Until (all 8 bits sent)

	LDA	BDREG		;go to quiescent state
	STA	BAUD
	PLA			;restore stack
	CLI			;re-enable interrupts
	RTS			;Return

	END