From 98df61229d47765f9626ad7a398bc6272a94ddeb Mon Sep 17 00:00:00 2001
From: Stuart Longland <me@vk4msl.id.au>
Date: Sat, 15 Jul 2017 15:59:49 +1000
Subject: [PATCH] attiny861 main: Use switch instead of if.

Years ago, and on MSP430 not AVR, I found that gcc produced tighter code
using `if` instead of `switch`.  Thus, I found myself always using `if`
and never `switch` if I needed branching, since smaller code is faster
code, and we needed all the speed we could get.

Turns out, AVR does not have this problem, and we get better performance
using `switch`.
---
 ports/attiny861/main.c | 72 +++++++++++++++++++++++-------------------
 1 file changed, 39 insertions(+), 33 deletions(-)

diff --git a/ports/attiny861/main.c b/ports/attiny861/main.c
index 96cffc7..571984d 100644
--- a/ports/attiny861/main.c
+++ b/ports/attiny861/main.c
@@ -237,41 +237,45 @@ ISR(TIMER0_COMPA_vect) {
 	static uint8_t gpio_state = GPIO_STATE_READ;
 	static uint8_t cur_light = 0;
 
-	if (gpio_state == GPIO_STATE_READ) {
-		/* We are reading inputs */
-		static uint8_t last = 0;
-		static uint8_t delay = DEBOUNCE_DELAY;
-		uint8_t now = ~PINA;
+	switch (gpio_state) {
+	case GPIO_STATE_READ:
+		{
+			/* We are reading inputs */
+			static uint8_t last = 0;
+			static uint8_t delay = DEBOUNCE_DELAY;
+			uint8_t now = ~PINA;
 
-		if (now != last) {
-			/*
-			 * We detected a change… reset
-			 * debounce timer
-			 */
-			last = now;
-			delay = DEBOUNCE_DELAY;
-		} else if (delay) {
-			/* Wait for bouncing to finish */
-			delay--;
-		} else {
-			/* Bouncing finished */
-			uint8_t diff;
+			if (now != last) {
+				/*
+				 * We detected a change… reset
+				 * debounce timer
+				 */
+				last = now;
+				delay = DEBOUNCE_DELAY;
+			} else if (delay) {
+				/* Wait for bouncing to finish */
+				delay--;
+			} else {
+				/* Bouncing finished */
+				uint8_t diff;
 
-			button_last = button_state;
-			button_state = now;
-			/* Determine differences from last */
-			diff = button_state ^ button_last;
-			/* Detect button presses & releases */
-			button_hit |= button_state & diff;
-			button_release |= (~button_state) & diff;
+				button_last = button_state;
+				button_state = now;
+				/* Determine differences from last */
+				diff = button_state ^ button_last;
+				/* Detect button presses & releases */
+				button_hit |= button_state & diff;
+				button_release |= (~button_state) & diff;
+			}
+			/* Turn off lights */
+			OCR1D = 0;
+			/* Switch to setting outputs */
+			PORTB &= ~GPIO_EN;
+			DDRA = 0xff;
+			gpio_state = GPIO_STATE_SELECT;
+			break;
 		}
-		/* Turn off lights */
-		OCR1D = 0;
-		/* Switch to setting outputs */
-		PORTB &= ~GPIO_EN;
-		DDRA = 0xff;
-		gpio_state = GPIO_STATE_SELECT;
-	} else if (gpio_state == GPIO_STATE_SELECT) {
+	case GPIO_STATE_SELECT:
 		/* We are setting outputs */
 		PORTA = (1 << cur_light);
 		/* Switch on input MUXes */
@@ -280,12 +284,14 @@ ISR(TIMER0_COMPA_vect) {
 		PORTA = 0xff;
 		DDRA = 0x00;
 		gpio_state = GPIO_STATE_PWM;
-	} else if (gpio_state == GPIO_STATE_PWM) {
+		break;
+	case GPIO_STATE_PWM:
 		OCR1D = light_output[cur_light];
 		/* Increment the light for later (modulo 8) */
 		cur_light++;
 		cur_light &= 0x07;
 		gpio_state = GPIO_STATE_READ;
+		break;
 	}
 
 	/* Tick down the one-second timer */