I2C: adding new "i2c bus" Command to the I2C Subsystem.

[karo-tx-uboot.git] / README

diff --git a/README b/README
index b10b539fa8d3362dc476a5e7b8dd20e4e5740e73..c63c72014147ab15a56a2ac1dfee0b166178445b 100644 (file)
--- a/README
+++ b/README
@@ -1429,6 +1429,53 @@ The following options need to be configured:
                Define this option if you want to use Freescale's I2C driver in
                drivers/i2c/fsl_i2c.c.
 
+               CONFIG_I2C_MUX
+
+               Define this option if you have I2C devices reached over 1 .. n
+               I2C Muxes like the pca9544a. This option addes a new I2C
+               Command "i2c bus [muxtype:muxaddr:muxchannel]" which adds a
+               new I2C Bus to the existing I2C Busses. If you select the
+               new Bus with "i2c dev", u-bbot sends first the commandos for
+               the muxes to activate this new "bus".
+
+               CONFIG_I2C_MULTI_BUS must be also defined, to use this
+               feature!
+
+               Example:
+               Adding a new I2C Bus reached over 2 pca9544a muxes
+                       The First mux with address 70 and channel 6
+                       The Second mux with address 71 and channel 4
+
+               => i2c bus pca9544a:70:6:pca9544a:71:4
+
+               Use the "i2c bus" command without parameter, to get a list
+               of I2C Busses with muxes:
+
+               => i2c bus
+               Busses reached over muxes:
+               Bus ID: 2
+                 reached over Mux(es):
+                   pca9544a@70 ch: 4
+               Bus ID: 3
+                 reached over Mux(es):
+                   pca9544a@70 ch: 6
+                   pca9544a@71 ch: 4
+               =>
+
+               If you now switch to the new I2C Bus 3 with "i2c dev 3"
+               u-boot sends First the Commando to the mux@70 to enable
+               channel 6, and then the Commando to the mux@71 to enable
+               the channel 4.
+
+               After that, you can use the "normal" i2c commands as
+               usual, to communicate with your I2C devices behind
+               the 2 muxes.
+
+               This option is actually implemented for the bitbanging
+               algorithm in common/soft_i2c.c and for the Hardware I2C
+               Bus on the MPC8260. But it should be not so difficult
+               to add this option to other architectures.
+
 
 - SPI Support: CONFIG_SPI