implement tax and inx and print status each time

1 files changed, 97 insertions, 17 deletions

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;
+}