w1: ds2438: support for writing to offset register

[linux-2.6-microblaze.git] / Documentation / w1 / slaves / w1_ds2438.rst

diff --git a/Documentation/w1/slaves/w1_ds2438.rst b/Documentation/w1/slaves/w1_ds2438.rst
index ac8d0d4..5c55739 100644 (file)
--- a/Documentation/w1/slaves/w1_ds2438.rst
+++ b/Documentation/w1/slaves/w1_ds2438.rst
@@ -22,7 +22,7 @@ is also often used in weather stations and applications such as: rain gauge,
 wind speed/direction measuring, humidity sensing, etc.
 
 Current support is provided through the following sysfs files (all files
-except "iad" are readonly):
+except "iad" and "offset" are readonly):
 
 "iad"
 -----
@@ -52,6 +52,15 @@ Internally when this file is read, the additional CRC byte is also obtained
 from the slave device. If it is correct, the 8 bytes page data are passed
 to userspace, otherwise an I/O error is returned.
 
+"offset"
+-------
+This file controls the 2-byte Offset Register of the chip.
+Writing a 2-byte value will change the Offset Register, which changes the
+current measurement done by the chip. Changing this register to the two's complement
+of the current register while forcing zero current through the load will calibrate
+the chip, canceling offset errors in the current ADC.
+
+
 "temperature"
 -------------
 Opening and reading this file initiates the CONVERT_T (temperature conversion)