shell: handle inputs with interrupts

parts/shell/shell.asm

@@ -27,8 +27,10 @@ BUFIDX		.equ	INPTBUF+BUFSIZE
 ; *** CODE ***
 	jr	init
 
+.fill 0x38-$
+	jr	handleInterrupt
+
 init:
-	; disable interrupts we don't need them
 	di
 
 	; setup stack
@@ -39,12 +41,16 @@ init:
 	xor	a
 	ld	(BUFIDX), a	; starts at 0
 
+	; RC2014's serial I/O is based on interrupt mode 1. We'd prefer im 2,
+	; but for now, let's go with the simpler im 1.
+	im	1
+
 	; setup ACIA
-	; CR7 (1) - Receive Interrupt disabled
+	; CR7 (1) - Receive Interrupt enabled
 	; CR6:5 (00) - RTS low, transmit interrupt disabled.
 	; CR4:2 (101) - 8 bits + 1 stop bit
 	; CR1:0 (10) - Counter divide: 64
-	ld	a, 0b00010110
+	ld	a, 0b10010110
 	out	(ACIA_CTL), a
 
 	; print prompt
@@ -52,11 +58,42 @@ init:
 	call	printstr
 	call	printcrlf
 
+	; alright, ready to receive
+	ei
+
 mainloop:
-	call	readc
 	call	chkbuf
 	jr	mainloop
 
+; read char in the ACIA and put it in the read buffer
+handleInterrupt:
+	push	af
+	push	hl
+
+	; Read our character from ACIA into our BUFIDX
+	in	a, (ACIA_CTL)
+	bit	0, a		; is our ACIA rcv buffer full?
+	jr	z, .end		; no? a interrupt was triggered for nothing.
+
+	call	getbufptr	; HL set, A set
+	; is our input buffer full? If yes, we don't read anything. Something
+	; is wrong: we don't process data fast enough.
+	cp	BUFSIZE
+	jr	z, .end		; if BUFIDX == BUFSIZE, our buffer is full.
+
+	; increase our buf ptr while we still have it in A
+	inc	a
+	ld	(BUFIDX), a
+
+	in	a, (ACIA_IO)
+	ld	(hl), a
+
+.end:
+	pop	hl
+	pop	af
+	ei
+	reti
+
 ; spits character in A in port SER_OUT
 printc:
 	push	af
@@ -85,43 +122,17 @@ printcrlf:
 	call	printc
 	ret
 
-; wait until a char is read in the ACIA and put it in the read buffer
-readc:
-	; first thing first: is our input buffer full? If yes, we don't even
-	; bother reading the ACIA. Something is wrong: we don't process data
-	; fast enough.
-	ld	a, (BUFIDX)
-	cp	BUFSIZE
-	ret	z		; if BUFIDX == BUFSIZE, our buffer is full.
-
-	call	getbufptr
-
-	; increase our buf ptr while we still have it in A
-	inc	a
-	ld	(BUFIDX), a
-
-.loop:
-	; Read our character from ACIA into our BUFIDX
-	in	a, (ACIA_CTL)
-	bit	0, a		; is our ACIA rcv buffer full?
-	jr	z, .loop	; no? loop
-
-	in	a, (ACIA_IO)
-	ld	(hl), a
-
-	ret
 
 ; check if the input buffer is full or ends in CR or LF. If it does, prints it
 ; back and empty it.
 chkbuf:
-	ld	a, (BUFIDX)
+	call	getbufptr
 	cp	0
 	ret	z		; BUFIDX is zero? nothing to check.
 
 	cp	BUFSIZE
 	jr	z, .do		; if BUFIDX == BUFSIZE? do!
 
-	call	getbufptr
 	; our previous char is in BUFIDX - 1. Fetch this
 	dec	hl
 	ld	a, (hl)		; now, that's our char we have in A
@@ -149,12 +160,17 @@ chkbuf:
 	ret
 
 ; Set current buffer pointer in HL. The buffer pointer is where our *next* char
-; will be written.
+; will be written. A is set to the value of (BUFIDX)
 getbufptr:
+	push	bc
+
+	ld	a, (BUFIDX)
 	ld	hl, INPTBUF
 	xor	b
 	ld	c, a
 	add	hl, bc		; hl now points to INPTBUF + BUFIDX
+
+	pop	bc
 	ret
 
 ; *** DATA ***