diff --git a/cpu.c b/cpu.c
index c5b35f6..076e887 100644
--- a/cpu.c
+++ b/cpu.c
@@ -51,20 +51,34 @@ uint8_t program[] = { 0xa9, 0xc0, 0xaa, 0xe8, 0x00 };
 
 uint32_t cycles = 0;
 
-uint8_t
+static uint8_t
 peek(uint16_t addr)
 {
 	return memory[addr];
 }
 
-uint16_t
+static uint16_t
 peek16(uint16_t addr)
 {
 	/* bytes are stored in little-endian (low then high) */
 	return (uint16_t)memory[addr] | ((uint16_t)memory[addr + 1] << 8);
 }
 
-uint8_t
+static void
+memwrite(uint16_t addr, uint8_t byte)
+{
+	memory[addr] = b;
+}
+
+static void
+memwrite16(uint16_t addr, uint16_t word)
+{
+	/* bytes are stored in little-endian (low then high) */
+	memory[addr] = word & 0xFF;
+	memory[addr + 1] = (word & 0xFF00) >> 8;
+}
+
+static uint8_t
 opcode_arg(enum addressing_mode mode)
 {
 	uint8_t arg, val;
@@ -597,7 +611,7 @@ unp(uint8_t arg)
 /* TODO: complete this */
 }
 
-void
+static void
 interpret(void)
 {
 	uint8_t opcode;