start working on 6502 cpu

1 files changed, 56 insertions, 0 deletions

diff --git a/cpu.c b/cpu.c
new file mode 100644
index 0000000..4a16835
--- /dev/null
+++ b/cpu.c
@@ -0,0 +1,56 @@
+#include <stdint.h>
+
+struct cpu_flags {
+        uint8_t carry : 1;
+        uint8_t zero : 1;
+        uint8_t interrupt_disable : 1;
+        uint8_t decimal_mode : 1;
+        uint8_t brk : 1;
+        uint8_t unused : 1;
+        uint8_t overflow : 1;
+        uint8_t negative : 1;
+};
+
+struct registers {
+        uint8_t acc, x, y, sp;
+        struct cpu_flags status;
+        uint16_t pc;
+};
+struct registers regs;
+
+enum addressing_mode {
+        AM_ACCUMULATOR,
+        AM_IMMEDIATE,
+        AM_ZERO_PAGE,
+        AM_ZERO_PAGE_X,
+        AM_ZERO_PAGE_Y,
+        AM_RELATIVE,
+        AM_ABSOLUTE,
+        AM_ABSOLUTE_X,
+        AM_ABSOLUTE_Y,
+        AM_INDIRECT,
+        AM_INDIRECT_X,
+        AM_INDIRECT_Y,
+        AM_INDEXED_INDIRECT,
+        AM_INDIRECT_INDEXED,
+};
+
+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 interpret(void)
+{
+        uint8_t opcode;
+        regs.pc = 0;
+
+        for (;;) {
+                opcode = program[regs.pc++];
+
+                switch (opcode) {
+                default:
+                        break;
+                }
+        }
+}