implement tax and inx and print status each time

2 files changed, 100 insertions, 17 deletions

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..4d0dfab
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,3 @@
+a.out
+*.core
+*~
diff --git a/cpu.c b/cpu.c
index 0843189..14c2ce3 100644
--- a/cpu.c
+++ b/cpu.c
@@ -1,4 +1,10 @@
 #include <stdint.h>
+#include <stdio.h>
+
+#define STATUS_UPDATE_ZERO(r)		\
+	(regs.status.zero = r == 0)
+#define STATUS_UPDATE_NEGATIVE(r)	\
+	(regs.status.negative = ((r & (1 << 7)) > 0))
 
 struct cpu_flags {
 	uint8_t carry : 1;
@@ -12,7 +18,7 @@ struct cpu_flags {
 };
 
 struct registers {
-	uint8_t acc, x, y, sp;
+	uint8_t a, x, y, sp;
 	struct cpu_flags status;
 	uint16_t pc;
 };
@@ -40,28 +46,64 @@ uint8_t addrbus[0x10000];
 /* example program taken from https://bugzmanov.github.io/nes_ebook/chapter_3_1.html */
 uint8_t program[] = { 0xa9, 0xc0, 0xaa, 0xe8, 0x00 };
 
-void brk(void)
+void
+brk(void)
 {
+	/* $00 */
 	/* TODO: push regs.pc and regs.status to stack and load IRQ vector */
 	regs.status.brk = 1;
 	return;
 }
 
-void lda(enum addressing_mode mode)
+void
+tax(void)
+{
+	/* $AA */
+	regs.x = regs.a;
+
+	STATUS_UPDATE_ZERO(regs.x);
+	STATUS_UPDATE_NEGATIVE(regs.x);
+}
+
+void
+inx(void)
+{
+	/* $E8 */
+	regs.x++;
+
+	STATUS_UPDATE_ZERO(regs.x);
+	STATUS_UPDATE_NEGATIVE(regs.x);
+}
+
+void
+lda(enum addressing_mode mode)
 {
 	uint8_t val;
 
 	switch (mode) {
 	case AM_IMMEDIATE:	/* $A9 */
 		val = program[regs.pc++];
-		regs.acc = val;
+		printf("arg1 $%02X\n", val);
+		regs.a = val;
 		break;
 	case AM_ZERO_PAGE:	/* $A5 */
+		/* TODO */
+		break;
 	case AM_ZERO_PAGE_X:	/* $B5 */
+		/* TODO */
+		break;
 	case AM_ABSOLUTE:	/* $AD */
+		/* TODO */
+		break;
 	case AM_ABSOLUTE_X:	/* $BD */
+		/* TODO */
+		break;
 	case AM_ABSOLUTE_Y:	/* $B9 */
+		/* TODO */
+		break;
 	case AM_INDIRECT_X:	/* $A1 */
+		/* TODO */
+		break;
 	case AM_INDIRECT_Y:	/* $B1 */
 		/* TODO */
 		break;
@@ -69,48 +111,86 @@ void lda(enum addressing_mode mode)
 		return;
 	}
 
-	regs.status.zero = regs.acc == 0;
-	regs.status.negative = (regs.acc & (1 << 7)) != 0;
+	STATUS_UPDATE_ZERO(regs.a);
+	STATUS_UPDATE_NEGATIVE(regs.a);
 }
 
-void interpret(void)
+void
+interpret(void)
 {
 	uint8_t opcode;
 	regs.pc = 0;
+	regs.status.unused = 1;
+
+	printf("Initial State:\n");
+	printf("status: %i%i%i%i%i%i%i%i\n", regs.status.carry,
+	    regs.status.zero, regs.status.interrupt_disable,
+	    regs.status.decimal_mode, regs.status.brk,
+	    regs.status.unused, regs.status.overflow,
+	    regs.status.negative);
+	printf("A: $%02X, X: $%02X, Y: $%02X, SP: $%02X, PC: $%02X\n",
+	    regs.a, regs.x, regs.y, regs.sp, regs.pc);
+
+	putchar('\n');
 
 	for (;;) {
 		opcode = program[regs.pc++];
 
+		printf("opcode: $%02X\n", opcode);
+
 		switch (opcode) {
 		case 0x00:
 			brk();
 			return;
-		case 0xa9:
-			lda(AM_IMMEDIATE);
+		case 0xa1:
+			lda(AM_INDIRECT_X);
 			break;
 		case 0xa5:
 			lda(AM_ZERO_PAGE);
 			break;
-		case 0xb5:
-			lda(AM_ZERO_PAGE_X);
+		case 0xa9:
+			lda(AM_IMMEDIATE);
+			break;
+		case 0xaa:
+			tax();
 			break;
 		case 0xad:
 			lda(AM_ABSOLUTE);
 			break;
-		case 0xbd:
-			lda(AM_ABSOLUTE_X);
+		case 0xb1:
+			lda(AM_INDIRECT_Y);
+			break;
+		case 0xb5:
+			lda(AM_ZERO_PAGE_X);
 			break;
 		case 0xb9:
 			lda(AM_ABSOLUTE_Y);
 			break;
-		case 0xa1:
-			lda(AM_INDIRECT_X);
+		case 0xbd:
+			lda(AM_ABSOLUTE_X);
 			break;
-		case 0xb1:
-			lda(AM_INDIRECT_Y);
+		case 0xe8:
+			inx();
 			break;
 		default:
+			printf("opcode $%02X not implemented\n", opcode);
 			break;
 		}
+
+		printf("status: %i%i%i%i%i%i%i%i\n", regs.status.carry,
+		    regs.status.zero, regs.status.interrupt_disable,
+		    regs.status.decimal_mode, regs.status.brk,
+		    regs.status.unused, regs.status.overflow,
+		    regs.status.negative);
+		printf("A: $%02X, X: $%02X, Y: $%02X, SP: $%02X, PC: $%02X\n",
+		    regs.a, regs.x, regs.y, regs.sp, regs.pc);
 	}
 }
+
+int
+main(void)
+{
+	interpret();
+
+	return 0;
+}