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--- en:xu3_hardware_i2c [2017/04/26 14:07]
charles.park
+++ en:xu3_hardware_i2c [2017/07/07 11:29] (current)
john1117 [How to change the I2C clock speed]
@@ Line 6: / Line 6: @@
 {{:en:xu3:xu3_i2c_with_expansion.png?700|}}
-You can use the devices via I2C-A(H/W I2C) or I2C-B(GPIO-I2C).
+You can use the devices via H/W I2C(I2C-A) or S/W I2C(I2C-B : GPIO-I2C).
 **H/W I2C (I2C-A)**
@@ Line 92: / Line 92: @@
-==== S/W I2C Signals ====
+===== How to change the I2C clock speed =====
-{{:en:weather_board:swi2c.png?500|}}
+To change the I2C clock speed, you need to modify the DT(Device Tree) file.\\
+Install required packages.
+<code>
+sudo apt-get install device-tree-compiler i2c-tools
+</code>
+Make a backup of DTB file.
+  * kernel 4.9.y
+<code>
+cp /media/boot/exynos5422-odroidxu4.dtb /media/boot/exynos5422-odroidxu4.dtb.org
+</code>
+  * kernel 3.10.y
+<code>
+cp /media/boot/exynos5422-odroidxu3.dtb /media/boot/exynos5422-odroidxu3.dtb.org
+</code>
+Using dtc command, you can make "dts" type of device tree from "dtb" type.
+  * kernel 4.9.y
+<code>
+dtc -I dtb -O dts -o exynos5422-odroidxu4.dts exynos5422-odroidxu4.dtb
+</code>
+  * kernel 3.10.y
+<code>
+dtc -I dtb -O dts -o exynos5422-odroidxu3.dts exynos5422-odroidxu3.dtb
+</code>
+And, open by an editor you like it and check the i2c path.
+<code>
+vi exynos5422-odroidxu4.dts
+--------------------------------------
+..
+/ {
+..
+    soc {
+..
+    i2c@12C70000 {
+..
+--------------------------------------
+</code>
+Check current maximum bus frequency of i2c@12C70000
+  * kernel 4.9.y
+<code>
+fdtget /media/boot/exynos5422-odroidxu4.dtb /soc/i2c@12C70000 samsung,i2c-max-bus-freq
+</code>
+  * kernel 3.10.y
+<code>
+fdtget /media/boot/exynos5422-odroidxu3.dtb /i2c@12C70000 samsung,i2c-max-bus-freq
+</code>
+Change the DTB file for i2c-1 (i2c channel #1)
+  * kernel 4.9.y
+<code>
+fdtput -t i /media/boot/exynos5422-odroidxu4.dtb /soc/i2c@12C70000 samsung,i2c-max-bus-freq "10000"
+sync
+reboot
+</code>
+  * kernel 3.10.y
+<code>
+fdtput -t i /media/boot/exynos5422-odroidxu3.dtb /i2c@12C70000 samsung,i2c-max-bus-freq "10000"
+sync
+reboot
+</code>
+If you want to go back to original 400Khz mode, change "10000" to "400000".\\
+**Actual I2C clock speed** (Measured with an oscilloscope)\\
+In 400Khz mode : 344.8khz \\
+In 100Khz mode : 63.7khz \\
+In 10Khz mode : 9.3Khz \\
+**Default I2C clock speed** \\
+XU4 : 400Khz mode \\