add lda immediate and brk

1 files changed, 60 insertions, 0 deletions

diff --git a/cpu.c b/cpu.c
index 4a16835..0843189 100644
--- a/cpu.c
+++ b/cpu.c
@@ -40,6 +40,39 @@ 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)
+{
+        /* TODO: push regs.pc and regs.status to stack and load IRQ vector */
+        regs.status.brk = 1;
+        return;
+}
+
+void lda(enum addressing_mode mode)
+{
+        uint8_t val;
+
+        switch (mode) {
+        case AM_IMMEDIATE:      /* $A9 */
+                val = program[regs.pc++];
+                regs.acc = val;
+                break;
+        case AM_ZERO_PAGE:      /* $A5 */
+        case AM_ZERO_PAGE_X:    /* $B5 */
+        case AM_ABSOLUTE:       /* $AD */
+        case AM_ABSOLUTE_X:     /* $BD */
+        case AM_ABSOLUTE_Y:     /* $B9 */
+        case AM_INDIRECT_X:     /* $A1 */
+        case AM_INDIRECT_Y:     /* $B1 */
+                /* TODO */
+                break;
+        default:
+                return;
+        }
+
+        regs.status.zero = regs.acc == 0;
+        regs.status.negative = (regs.acc & (1 << 7)) != 0;
+}
+
 void interpret(void)
 {
         uint8_t opcode;
@@ -49,6 +82,33 @@ void interpret(void)
                 opcode = program[regs.pc++];
 
                 switch (opcode) {
+                case 0x00:
+                        brk();
+                        return;
+                case 0xa9:
+                        lda(AM_IMMEDIATE);
+                        break;
+                case 0xa5:
+                        lda(AM_ZERO_PAGE);
+                        break;
+                case 0xb5:
+                        lda(AM_ZERO_PAGE_X);
+                        break;
+                case 0xad:
+                        lda(AM_ABSOLUTE);
+                        break;
+                case 0xbd:
+                        lda(AM_ABSOLUTE_X);
+                        break;
+                case 0xb9:
+                        lda(AM_ABSOLUTE_Y);
+                        break;
+                case 0xa1:
+                        lda(AM_INDIRECT_X);
+                        break;
+                case 0xb1:
+                        lda(AM_INDIRECT_Y);
+                        break;
                 default:
                         break;
                 }