Added, clear, jmp, ld, add, set and draw ops.

Also cleaned up comments for now will add better clear ones later down
the line for future reference.

src/machine/cpu.odin

@@ -31,19 +31,87 @@ cycle :: proc(s: ^System) {
         switch opcode {
             case 0x00E0: op_cls(s)
         }
-    case 0x1: op_jp_add(s)
-    case 0xD: log.info("D instruction a draw call!")
+    case 0x1: op_jp_add(s, opcode)
+    case 0x6: op_ld(s, opcode)
+    case 0x7: op_add(s, opcode)
+    case 0xA: op_set(s, opcode)
+    case 0xD: op_draw(s, opcode)
     }
 }
 
+debug_opcode :: proc(opcode: u16) {
+    log.debugf("opcode: 0x%04X", opcode)
+}
+
 // Instruction procs
 // -----------------------------------
 // CLS: Clear the display
 op_cls :: proc(s: ^System) {
-    log.info("found clear screen instruction, zero out display buffer")
+    // log.info("found clear screen instruction, zero out display buffer")
+
+    // Odin lets you zero a fixed array with just: {} is the zero value,
+    // so it clears the entire buffer in one shot.
+    s.display = {}
 }
 
 // JP addr: Jump to location nnn
-op_jp_add :: proc(s: ^System) {
-    log.info("found jump instruction, set pc to nnn")
+op_jp_add :: proc(s: ^System, opcode: u16) {
+    addr := (opcode & 0x0FFF)
+    s.pc = addr
+}
+
+// LD: Load value kk into x register
+op_ld :: proc(s: ^System, opcode: u16) {
+    register := (opcode & 0x0F00) >> 8
+    value := (opcode & 0x00FF)
+
+    s.v[register] = u8(value)
+}
+
+// ADD: Adds the value kk to the value of register Vx, then stores the result in Vx.
+op_add :: proc(s: ^System, opcode: u16) {
+    register := (opcode & 0x0F00) >> 8
+    value := (opcode & 0x00FF)
+    s.v[register] += u8(value)
+}
+
+// SET: The value of register I is set to nnn.
+op_set :: proc(s: ^System, opcode: u16) {
+    index_addr := (opcode & 0x0FFF)
+    s.i = index_addr
+}
+
+// DRAW: Display n-byte sprite starting at memory location I at (Vx, Vy), set VF = collision.
+op_draw :: proc(s: ^System, opcode: u16) {
+    x_register := (opcode & 0x0F00) >> 8
+    y_register := (opcode & 0x00F0) >> 4
+
+    // Handle wrapping
+    x_coord := (s.v[x_register] & 0x03F)
+    y_coord := (s.v[y_register] & 0x1F)
+
+    s.v[0xF] = 0
+
+    n_bytes := (opcode & 0x000F)
+
+    for row in 0..<n_bytes {
+        sprite_row := s.memory[s.i + row]
+        // log.debugf("sr: 0x%X", sprite_row)
+
+        for col in 0..<8 {
+            mask := u8(0x80) >> u8(col)
+
+            if sprite_row & mask != 0 {
+                // this bit is set Xor the pixel
+                y_pos := ((y_coord + u8(row)) % 32)
+                x_pos := ((x_coord + u8(col)) % 64)
+
+                pixel := &s.display[y_pos][x_pos]
+                if pixel^ == 1 {
+                    s.v[0xF] = 1
+                }
+                pixel^ = pixel^ ~ 1
+            }
+        }
+    }
 }