From e1868033d66f127dda2db4c9d5f636e404b05b00 Mon Sep 17 00:00:00 2001
From: Jonathan McDowell <noodles@earth.li>
Date: Thu, 10 May 2018 08:03:19 +0100
Subject: [PATCH] Add w1_read_bit() to improve waiting for result

Rather than using a full w1_read_byte() to wait for the temperature
sensor to indicate a result is ready introduce a w1_read_bit() and
use that instead. This lets us service USB requests more often while
waiting for the result.
---
 main.c |  2 +-
 w1.c   | 37 +++++++++++++++++++++++--------------
 w1.h   |  1 +
 3 files changed, 25 insertions(+), 15 deletions(-)

diff --git a/main.c b/main.c
index 61064a0..a75a4fc 100644
--- a/main.c
+++ b/main.c
@@ -426,7 +426,7 @@ int main(void)
 			w1_write(0x44);		/* Convert T */
 			temp_state = 4;
 		} else if (temp_state == 4) {
-			if (w1_read_byte() == 0xFF)
+			if (w1_read_bit())
 				temp_state = 5;
 		} else if (temp_state == 5) {
 			if (w1_reset()) {
diff --git a/w1.c b/w1.c
index 8217602..add1b48 100644
--- a/w1.c
+++ b/w1.c
@@ -65,26 +65,35 @@ void w1_write(uint8_t val)
 	}
 }
 
+bool w1_read_bit()
+{
+	bool val;
+
+	ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
+	{
+		/* Pull low for 6µs */
+		DDRB |= 1 << W1_PIN;
+		_delay_us(6);
+		/* Release for 9µs */
+		DDRB &= ~(1 << W1_PIN);
+		_delay_us(9);
+
+		/* Read the line state */
+		val = ((PINB >> W1_PIN) & 1);
+	}
+	_delay_us(55);
+
+	return val;
+}
+
 uint8_t w1_read_byte()
 {
 	uint8_t i, val;
 
 	val = 0;
 	for (i = 0; i < 8; i++) {
-		ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
-		{
-			/* Pull low for 6µs */
-			DDRB |= 1 << W1_PIN;
-			_delay_us(6);
-			/* Release for 9µs */
-			DDRB &= ~(1 << W1_PIN);
-			_delay_us(9);
-
-			/* Read the line state */
-			val |= ((PINB >> W1_PIN) & 1) << i;
-		}
-
-		_delay_us(55);
+		if (w1_read_bit())
+			val |= (1 << i);
 	}
 
 	return val;
diff --git a/w1.h b/w1.h
index 54c9f5b..bef02a9 100644
--- a/w1.h
+++ b/w1.h
@@ -5,6 +5,7 @@
 
 uint8_t w1_crc(uint8_t *buf, uint8_t len);
 void w1_write(uint8_t val);
+bool w1_read_bit();
 uint8_t w1_read_byte();
 void w1_read(uint8_t *buf, uint8_t len);
 bool w1_reset(void);
-- 
2.39.2