Some tidying, starting to work on a cooler demo.

cpu.h

@@ -14,7 +14,10 @@
 #define FLAG_ZERO 0x02
 #define FLAG_CARRY 0x01
 
+// set if memory was modified during processing of the last instruction
 #define EMU_FLAG_DIRTY 0x01
+// set if the emulator should wait for an interrupt before continuing
+#define EMU_FLAG_WAIT_FOR_INTERRUPT 0x02
 
 typedef struct {
     // program counter

debug.c

@@ -9,15 +9,15 @@ void dump_cpu(cpu *m) {
     init_names();
 
     int i;
-    printf("pc %04X\nx %02X y %02X sp %02X sr %02X ac %02X",
+    fprintf(stderr, "pc %04X\nx %02X y %02X sp %02X sr %02X ac %02X",
             m->pc, m->x, m->y, m->sp, m->sr, m->ac);
 
-    printf("\nlast opcode: %s (%02X)",
+    fprintf(stderr, "\nlast opcode: %s (%02X)",
             inst_names[m->last_opcode], m->last_opcode);
-    printf(", next opcode: %s (%02X)",
+    fprintf(stderr, ", next opcode: %s (%02X)",
             inst_names[m->mem[m->pc]], m->mem[m->pc]);
 
-    printf("\nflags n %d o %d b %d d %d i %d z %d c %d",
+    fprintf(stderr, "\nflags n %d o %d b %d d %d i %d z %d c %d",
             (m->sr & FLAG_NEGATIVE) > 0,
             (m->sr & FLAG_OVERFLOW) > 0,
             (m->sr & FLAG_BREAK) > 0,
@@ -26,35 +26,35 @@ void dump_cpu(cpu *m) {
             (m->sr & FLAG_ZERO) > 0,
             (m->sr & FLAG_CARRY) > 0);
 
-    printf("\nmem   ");
+    fprintf(stderr, "\nmem   ");
 
     int mem_offset = m->pc - MEM_PRINT_BYTES / 2;
     // clamp to [0, MAX_MEM_OFFSET]
     mem_offset = mem_offset < 0 ? 0 : (
             mem_offset > MAX_MEM_OFFSET ? MAX_MEM_OFFSET : mem_offset);
 
     for (i = 0; i < MEM_PRINT_BYTES; i++) {
-        printf("%02X ", m->mem[i + mem_offset]);
+        fprintf(stderr, "%02X ", m->mem[i + mem_offset]);
     }
 
-    printf("\n      ");
+    fprintf(stderr, "\n      ");
     for (i = 0; i < m->pc - mem_offset; i++) {
-        printf("   ");
+        fprintf(stderr, "   ");
     }
-    printf("^^ (%04x)", m->pc);
+    fprintf(stderr, "^^ (%04x)", m->pc);
 
-    printf("\nstack ");
+    fprintf(stderr, "\nstack ");
     for (i = 0; i < MEM_PRINT_BYTES; i++) {
-        printf("%02X ", m->mem[STACK_START + 0xFF - i]);
+        fprintf(stderr, "%02X ", m->mem[STACK_START + 0xFF - i]);
     }
     int off = 0xFF - m->sp;
     if (off < MEM_PRINT_BYTES) {
-        printf("\n      ");
+        fprintf(stderr, "\n      ");
         for (i = 0; i < off; i++) {
-            printf("   ");
+            fprintf(stderr, "   ");
         }
-        printf("^^");
+        fprintf(stderr, "^^");
     }
 
-    printf("\n\n");
+    fprintf(stderr, "\n\n");
 }

emu.c

@@ -26,10 +26,6 @@ void main_loop(cpu *m) {
     // after we move to the next instruction
     int8_t branch_offset = 0;
 
-    // if set to true, the next instruction will not be executed until an
-    // interrupt is fired from the IO bus and handled.
-    uint8_t wait_for_interrupt = 0;
-
     init_io();
 
     for (;;) {
@@ -81,8 +77,11 @@ void main_loop(cpu *m) {
 
         do {
             handle_io(m);
-        } while (wait_for_interrupt && !m->interrupt_waiting);
-        wait_for_interrupt = 0;
+            // clear dirty memory flag immediately so that subsequent runs don't
+            // redo whatever I/O operation is associated with the dirty memaddr
+            m->emu_flags &= ~EMU_FLAG_DIRTY;
+        } while ((m->emu_flags & EMU_FLAG_WAIT_FOR_INTERRUPT) &&
+                 !m->interrupt_waiting);
 
         if (m->interrupt_waiting && !get_flag(m, FLAG_INTERRUPT)) {
             STACK_PUSH(m) = (m->pc & 0xFF00) >> 8;

io.c

@@ -25,6 +25,7 @@ void init_io() {
     noecho();
     nodelay(stdscr, TRUE);
     keypad(stdscr, TRUE);
+    curs_set(0);
 
     io_supports_paint = (has_colors() != FALSE);
     if (io_supports_paint) {
@@ -50,6 +51,7 @@ void finish_io() {
 void init_vterm() {
     window = newwin(VTERM_ROWS + 2, VTERM_COLS + 2, 0, 0);
     box(window, 0, 0);
+    wrefresh(window);
 }
 
 void finish_vterm() {
@@ -59,6 +61,7 @@ void finish_vterm() {
 void update_modeflags(uint8_t old_flags, uint8_t new_flags) {
     io_modeflags = new_flags;
 
+    // if the vterm flag changed (avoids reinit every time flags change)
     if ((new_flags ^ old_flags) & IO_MODEFLAG_VTERM) {
         if (new_flags & IO_MODEFLAG_VTERM) {
             init_vterm();

opcode_handlers/interrupts.h

@@ -10,5 +10,5 @@ case RTI:
     break;
 
 case WAI:
-    wait_for_interrupt = 1;
+    m->emu_flags |= EMU_FLAG_WAIT_FOR_INTERRUPT;
     break;

sample_programs/minigame.s

@@ -0,0 +1,91 @@
+#include <stdio.s>
+
+rows = 25
+cols = 40
+
+; load location of ISR
+        lda     #<isr
+        sta     $FFFE
+        lda     #>isr
+        sta     $FFFF
+
+; activate vterm mode
+        lda     #$01
+        sta     $FF02
+
+; shiny pretty colors
+        lda     #$04
+        sta     paint
+
+; register and addressing init
+        lda     #$00
+        sta     $00
+        lda     #$FB
+        sta     $01
+
+        lda     #$A4
+        ldy     #$00
+
+        cli
+
+loop
+        sta     ($00),Y
+        wai
+        jmp     loop
+
+isr:
+        pha
+
+        ; clear existing character
+        lda     #$20
+        sta     ($00),Y
+
+        lda     getc
+
+        cmp     #$71    ; 71 == 'q'
+        bne     checkj
+        ext
+
+checkj:
+        cmp     #$6A    ; 6A == 'j'
+        bne     checkk
+        ; it's a j. move down.
+        tya
+        clc
+        adc     #cols
+        jmp     checkbounds
+
+checkk:
+        cmp     #$6B    ; 6B == 'k'
+        bne     checkh
+        ; it's a k. move up.
+        tya
+        sec
+        sbc     #cols
+        jmp     checkbounds
+
+checkh:
+        cmp     #$68    ; 68 == 'h'
+        bne     checkl
+        ; it's an h. move left.
+        tya
+        sec
+        sbc     #$02
+        jmp     checkbounds
+
+checkl:
+        cmp     #$6C    ; 6C == 'l'
+        bne     done
+        ; it's an h. move left.
+        tya
+        clc
+        adc     #$02
+        jmp     checkbounds
+
+checkbounds:
+        ; TODO
+        tay
+
+done:
+        pla
+        rti

stdlib/stdio.s

@@ -2,6 +2,8 @@
 
 putc = $FF00
 getc = $FF01
+iomode = $FF02
+paint = $FEE8
 
 #define debug .byt $FC
 #define ext .byt $FF