ACIA interrupt handling

samples/README

@@ -6,18 +6,22 @@ Sample Programs
   When loaded at address $0300, this program will print "Hello, 6502 World!" in
   infinite loop.
 
-2. echo.prg
+2. echo_poll.prg
 
   When loaded at address $0300, this program will echo back to the console
   anything typed.
 
 
-Both hello.prg and echo.prg were assembled with the Ophis assembler:
+Both hello.prg and echo_poll.prg were assembled with the Ophis assembler:
 
    https://hkn.eecs.berkeley.edu/~mcmartin/ophis/
 
+3. echo_irq.rom
 
-3. ehbasic.rom
+  This is another echo program, and behaves identically to echo_poll.prg,
+  except it is interrupt-driven.
+
+4. ehbasic.rom
 
    This is Lee Davison's Enhanced 6502 BASIC.
 

samples/echo_irq/.gitignore

@@ -0,0 +1,4 @@
+*.rom
+*.lst
+*.map
+*.o

samples/echo_irq/Makefile

@@ -0,0 +1,13 @@
+CA=ca65
+LD=ld65
+
+all: echo_irq
+
+echo_irq: echo_irq.o
+	$(LD) -C symon.config -vm -m echo_irq.map -o echo_irq.rom echo_irq.o
+
+echo_irq.o:
+	$(CA) --listing -o echo_irq.o echo_irq.asm
+
+clean:
+	rm -f *.o *.rom *.map *.lst

samples/echo_irq/echo_irq.asm

@@ -0,0 +1,48 @@
+;;
+;; Read input from the keyboard, and echo to console.
+;;
+
+
+IOBASE   = $8800
+IOSTATUS = IOBASE + 1
+IOCMD    = IOBASE + 2
+IOCTRL   = IOBASE + 3
+
+.segment "CODE"
+.org $C000
+
+START:  CLI
+        LDA #$09
+        STA IOCMD      ; Set command status
+        LDA #$1A
+        STA IOCTRL     ; 0 stop bits, 8 bit word, 2400 baud
+
+;;
+;; Infinite idle loop, waiting for interrupt.
+;;
+IDLE:   LDA #$FF
+        TAX
+IDLE1:  DEX
+        BNE IDLE1
+        JMP IDLE
+
+;;
+;; IRQ handler
+;;
+IRQ:    LDA IOBASE      ; Get the character in the ACIA.
+        PHA             ; Save accumulator
+ECHO1:  LDA IOSTATUS    ; Read the ACIA status
+        AND #$10        ; Is the tx register empty?
+        BEQ ECHO1       ; No, wait for it to empty
+        PLA             ; Otherwise, load saved accumulator,
+        STA IOBASE      ; write to output,
+        RTI             ; and return
+
+; system vectors
+
+.segment "VECTORS"
+.org    $FFFA
+
+.word   IRQ         ; NMI vector
+.word   START       ; RESET vector
+.word   IRQ         ; IRQ vector

samples/echo_irq/symon.config

@@ -0,0 +1,16 @@
+MEMORY {
+RAM1: start = $0000, size = $8000;
+ROM1: start = $C000, size = $3FFA, fill = yes;
+ROMV: start = $FFFA, size = $6, file = %O, fill = yes;
+}
+
+SEGMENTS {
+CODE:     load = ROM1, type = ro;
+DATA:     load = ROM1, type = ro;
+VECTORS:  load = ROMV, type = ro;
+}
+
+SYMBOLS {
+__STACKSIZE__ = $0300;
+}
+