diff --git a/labsw/fw/labsw.c b/labsw/fw/labsw.c
index d92fa1f..e7634e2 100644
--- a/labsw/fw/labsw.c
+++ b/labsw/fw/labsw.c
@@ -24,7 +24,60 @@
 int local = 1;
 
 
-#define	DEBOUNCE_CYCLES	10
+/*
+ * SDCC complains a lot about code that's unreachable due to constant
+ * conditional expressions.
+ */
+
+#pragma disable_warning 126	/* unreachable code */
+
+
+/* ----- Button debouncing ------------------------------------------------- */
+
+
+/* In the version of 2011-09-11, 10000 cycles are about 128 ms */
+
+#define	PREBOUNCE_CYCLES	2000
+#define	POSTBOUNCE_CYCLES	5000
+
+
+#define	TURN(ch, on)			\
+	do {				\
+		CH##ch##_RELAY = on;	\
+		CH##ch##_OPT = !on;	\
+		if (on)			\
+			LED(CH##ch, R);	\
+		else			\
+			LED(CH##ch, G);	\
+	} while (0)
+
+
+#define	DEBOUNCE(BUT, but)					\
+	do {							\
+		last_##but = but_##but;				\
+		if (postbounce_##but) {				\
+			postbounce_##but--;			\
+			break;					\
+		}						\
+		if (but_##but == !BUT_##BUT) {			\
+			prebounce_##but = 0;			\
+			break;					\
+		}						\
+		if (prebounce_##but != PREBOUNCE_CYCLES) {	\
+			prebounce_##but++;			\
+			break;					\
+		}						\
+		prebounce_##but = 0;				\
+		postbounce_##but = POSTBOUNCE_CYCLES;		\
+		but_##but = !but_##but;				\
+	} while (0)
+
+
+#define	PRESSED(but)	(but_##but && !last_##but)
+#define	RELEASED(but)	(!but_##but && last_##but)
+
+
+/* ----- LED and channel control ------------------------------------------- */
 
 
 #define	IS_ON(ch)	(CH##ch##_RELAY || !CH##ch##_OPT)
@@ -36,21 +89,15 @@ int local = 1;
 #define	LED_G_COLOR_G	1
 #define	LED_G_COLOR_OFF	0
 
+
 #define	LED(ch, color)					\
 	do {						\
 		LED_##ch##_R = LED_R_COLOR_##color;	\
 		LED_##ch##_G = LED_G_COLOR_##color;	\
 	} while (0)
 
-#define	TURN(ch, on)			\
-	do {				\
-		CH##ch##_RELAY = on;	\
-		CH##ch##_OPT = !on;	\
-		if (on)			\
-			LED(CH##ch, R);	\
-		else			\
-			LED(CH##ch, G);	\
-	} while (0)
+
+/* ----- I/O setup --------------------------------------------------------- */
 
 
 static void init_io(void)
@@ -78,11 +125,15 @@ static void init_io(void)
 }
 
 
+/* ----- Main loop --------------------------------------------------------- */
+
+
 void main(void)
 {
-	int debounce_main = 0, last_main = 0, but_main = 0;
-	int debounce_ch1 = 0, last_ch1 = 0, but_ch1 = 0;
-	int debounce_ch2 = 0, last_ch2 = 0, but_ch2 = 0;
+	int prebounce_main = 0, postbounce_main = 0;
+	int last_main = 0, but_main = 0;
+	int prebounce_ch1 = 0, postbounce_ch1 = 0, last_ch1 = 0, but_ch1 = 0;
+	int prebounce_ch2 = 0, postbounce_ch2 = 0, last_ch2 = 0, but_ch2 = 0;
 	init_io();
 
 	usb_init();
@@ -93,34 +144,15 @@ void main(void)
 	TURN(2, 0);
 
 	while (1) {
-		if (debounce_main)
-			debounce_main--;
-		else {
-			last_main = but_main;
-			but_main = !BUT_MAIN;
-			if (last_main != but_main)
-				debounce_main = DEBOUNCE_CYCLES;
-		}
+		DEBOUNCE(MAIN, main);
+		DEBOUNCE(CH1, ch1);
+		DEBOUNCE(CH2, ch2);
 
-		if (debounce_ch1)
-			debounce_ch1--;
-		else {
-			last_ch1 = but_ch1;
-			but_ch1 = !BUT_CH1;
-			if (last_ch1 != but_ch1)
-				debounce_ch1 = DEBOUNCE_CYCLES;
-		}
-
-		if (debounce_ch2)
-			debounce_ch2--;
-		else {
-			last_ch2 = but_ch2;
-			but_ch2 = !BUT_CH2;
-			if (last_ch2 != but_ch2)
-				debounce_ch2 = DEBOUNCE_CYCLES;
-		}
-
-		if (but_main && !last_main) {
+		/*
+		 * Pressing MAIN forces local mode. Pressing it in local mode,
+		 * it turns off both front channels.
+		 */
+		if (PRESSED(main)) {
 			if (local) {
 				TURN(1, 0);
 				TURN(2, 0);
@@ -128,6 +160,9 @@ void main(void)
 			local = 1;
 		}
 
+		/*
+		 * Update LEDs in local mode.
+		 */
 		if (local) {
 			LED(MAIN, G);
 			if (IS_ON(1))
@@ -140,10 +175,14 @@ void main(void)
 				TURN(2, 0);
 		}
 
+		/*
+		 * In local mode, buttons CH1 and CH2 toggle the respective
+		 * channel.
+		 */
 		if (local) {
-			if (but_ch1 && !last_ch1)
+			if (PRESSED(ch1))
 				TURN(1, !IS_ON(1));
-			if (but_ch2 && !last_ch2)
+			if (PRESSED(ch2))
 				TURN(2, !IS_ON(2));
 		}