From b2611d6be305c94359f67df875786858e05c3eb0 Mon Sep 17 00:00:00 2001
From: syndycat <syndycat@yahoo.com>
Date: Sat, 7 Jan 2017 13:36:11 +0200
Subject: [PATCH] drivers/onewire/ds18x20: Fix negative temperature calc for
 DS18B20.

---
 drivers/onewire/ds18x20.py | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/drivers/onewire/ds18x20.py b/drivers/onewire/ds18x20.py
index a2f7f5c3da..342f4b28ae 100644
--- a/drivers/onewire/ds18x20.py
+++ b/drivers/onewire/ds18x20.py
@@ -93,6 +93,9 @@ class DS18X20(object):
             temp = temp_read - 0.25 + (count_per_c - count_remain) / count_per_c
             return temp
         elif rom0 == 0x28:
-            return (temp_msb << 8 | temp_lsb) / 16
+            temp = (temp_msb << 8 | temp_lsb) / 16
+            if (temp_msb & 0xf8) == 0xf8: # for negative temperature
+                temp -= 0x1000
+            return temp
         else:
             assert False