diff --git a/atusb/fw/mac.c b/atusb/fw/mac.c
index 33c891b..05d16d6 100644
--- a/atusb/fw/mac.c
+++ b/atusb/fw/mac.c
@@ -34,6 +34,9 @@ static bool queued_rx = 0;
 static uint8_t next_seq, this_seq, queued_seq;
 
 
+/* ----- Register access --------------------------------------------------- */
+
+
 static uint8_t reg_read(uint8_t reg)
 {
 	uint8_t value;
@@ -56,6 +59,9 @@ static void reg_write(uint8_t reg, uint8_t value)
 }
 
 
+/* ----- Interrupt handling ------------------------------------------------ */
+
+
 static void receive_frame(void);
 
 
@@ -137,6 +143,9 @@ static bool handle_irq(void)
 }
 
 
+/* ----- TX/RX ------------------------------------------------------------- */
+
+
 static void change_state(uint8_t new)
 {
 	while ((reg_read(REG_TRX_STATUS) & TRX_STATUS_MASK) ==