/ vim: set sw=8 noexpandtab :

*000

INTRET,	0
	JMP GOTINT

INPUTY,	1000	/ Address of youngest byte in input buffer
INPUTO,	1000	/ Address of oldest byte in input buffer

*200

/ Main program enables keyboard interrupt, then enters echo loop
	KIE
	ION
LOOP,	TSF		/ Call ECHO if printer is ready
	JMS ECHO
	JMP LOOP

ECHO,	0
	TAD INPUTO
	CMA IAC		/ Negate
	TAD INPUTY
	SNA		/ Abandon echo if input buffer is empty (n.b. or full, because we don't have wrap bits)
	JMP I ECHO
	TAD I INPUTO	/ Read from input buffer
	TLS		/ Print
	JMS FIXO
	JMP I ECHO

GOTINT,	KSF		/ Skip reading keyboard if nothing was typed
	JMP NOIN
	DCA SAVED
	KRB		/ Read from keyboard
	DCA I INPUTY	/ Write to input buffer
	JMS FIXY
	CLA
	TAD SAVED
NOIN,	RMF
	ION
	JMP I INTRET

/ Wrap INPUTY pointer at 2000 back to 1000
FIXY,	0
	TAD INPUTY
	TAD [-2000]
	SZA
	JMP I FIXY
	CLA
	TAD [1000]
	DCA INPUTY
	JMP I FIXY

/ Wrap INPUTO pointer at 2000 back to 1000
FIXO,	0
	TAD INPUTO
	TAD [-2000]
	SZA
	JMP I FIXO
	CLA
	TAD [1000]
	DCA INPUTO
	JMP I FIXO

*300

SAVED,	0