Pi4J MCP23017 gives "Failed to select slave device"

[twocats]

Hi All,
I have a raspberry B rev2 (revision 000f from /proc/cpuinfo)
I'm running Raspbian GNU/Linux 8 (jessie) kernel 4.4.37+ #936 Fri Dec 9 16:53:10 GMT 2016 armv6l
/boot/config has dtoverlay=mcp23017 (with or without this the error still occurs)
(with the dtoverlay) the MCP23017 device is recognised and is presented to the /sys FS as
/sys/devices/platform/soc/20804000.i2c/i2c-1/1-0020/gpio/gpiochip496

using the example MCP23017GpioExample code - having changed the provider line to:

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provider = new MCP23017GpioProvider(I2CBus.BUS_1, 0x20);

when i run

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java -cp pi4j-example-1.2-SNAPSHOT.jar:pi4j-core-1.2-20161229.215408-19.jar:pi4j-device-1.2-20161229.215426-19.jar:pi4j-gpio-extension-1.2-20161229.215417-19.jar MCP23017GpioExample

I get the error :

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<--Pi4J--> MCP23017 GPIO Example ... started.
Exception in thread "main" com.pi4j.io.i2c.I2CIOException: Failed to select slave device!
	at com.pi4j.io.i2c.impl.I2CBusImpl.selectBusSlave(I2CBusImpl.java:284)
	at com.pi4j.io.i2c.impl.I2CBusImpl.runBusLockedDeviceAction(I2CBusImpl.java:243)

Any thoughts?

[DougieLawson]

Is your MCP23017 connected correctly? Have you tied the A0, A1 & A2 pins to GND?

What does i2cdetect -y 1 show?
You may need to use sudo apt-get install i2c-tools to get that program available for you.

[twocats]

Yes its connected correctly - I can control it directly using the /sys filing system.
It will happily read and change the output. Either by just simple command line commands
or via python.

i2c shows this :

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

which in case the formatting is incorrect shows I have 2 devices - the MCP at address 0x20 and the RTC at 0x68

If on the command line I do

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echo 496 > /sys/class/gpio/export
echo out > /sys/class/gpio/gpio496/direction
echo 1 > /sys/class/gpio/gpio496/value 
sleep 1 
echo 0 > /sys/class/gpio/gpio496/value 

it will change the output correctly.
likewise I can do the same and it will read correctly.

[DougieLawson]

That 'UU' status means the device has been captured by the kernel and isn't available for userspace programs. So if your Java program doesn't use the /sys filesystem interface you'll need to remove that overlay for the MCP23017 and reboot.

The stuff here: https://github.com/Pi4J/pi4j/blob/maste ... ample.java doesn't need the overlay. It uses /dev/i2c-1 driving that with the Java native interface (JNI) code in com_pi4j_wiringpi_I2C.c.

[twocats]

Ace that works!
(I've black listed gpio_mcp23s08 as well for good measure!)
Thanks!