PhilBot PhilBot - 1 month ago 12
Linux Question

OMAP 3 Linux I2C SMBUS SmartBattery (SBS) not Detected

I am working on an embedded Linux project with the OMAP 3730. We are using version 3.2.23 of the Kernel. I2C works fine and I can see various sensors from the board on bus #2. I2C bus #3 only has a Smart Battery attached and I can remove the power cord and the battery keeps the board running. The issue is that I cannot detect or otherwise scan for the smart battery. I've tried the various programs in i2ctools with no luck. We hooked the board up to the scope and can see activity on the bus #3. I have also enabled every pertinent option under the Device Drivers > I2C Support in the Kernel.

How can I view my smart battery on the i2c bus? Do I need to enable something else in the Kernel?

Standard SMBus slave address assignments for SBS devices include:
0x10 -- SMBus System Host
0x12 -- Smart Battery Charger
0x14 -- Smart Battery Selector
0x16 -- Smart Battery

# ls /dev/i2c-?
/dev/i2c-1 /dev/i2c-2 /dev/i2c-3

# i2cget -y 3 0x10 0x00 w p
Error: Read failed
#
# i2cget -y 3 0x0b 0x00 w p
Error: Read failed

# i2cdetect -r 3
WARNING! This program can confuse your I2C bus, cause data loss and worse!
I will probe file /dev/i2c-3 using read byte commands.
I will probe address range 0x03-0x77.
Continue? [Y/n] y
0 1 2 3 4 5 6 7 8 9 a b c d e f
00: -- -- -- -- -- -- -- -- -- -- -- -- --
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --
70: -- -- -- -- -- -- -- --

# i2cdetect -F 3
Functionalities implemented by /dev/i2c-3:
I2C yes
SMBus Quick Command no
SMBus Send Byte yes
SMBus Receive Byte yes
SMBus Write Byte yes
SMBus Read Byte yes
SMBus Write Word yes
SMBus Read Word yes
SMBus Process Call yes
SMBus Block Write yes
SMBus Block Read no
SMBus Block Process Call no
SMBus PEC yes
I2C Block Write yes
I2C Block Read yes

# i2cdetect -l
i2c-1 i2c OMAP I2C adapter I2C adapter
i2c-2 i2c OMAP I2C adapter I2C adapter
i2c-3 i2c OMAP I2C adapter I2C adapter

Answer

The solution was to decrease the bus speed to 100 KHz for the bus that the gas gauge chip was on. After that I get:

# i2cdetect -y -r 3
     0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
00:          -- -- -- -- -- -- -- -- 0b -- -- -- -- 
10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
40: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
70: -- -- -- -- -- -- -- --