Difference between revisions of "Application note - GPIO on fitlet2 with FC-SCG running Linux"
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Revision as of 08:32, 27 September 2018
fitlet2 supports I2C GPIO extender if configured with the FC-SCG FACET
I2c gpio extender binding and usage
1. Make sure that the kernel you use supports the necessary driver. Check the following entries in the kernel config:
CONFIG_GPIO_PCA953X=[y] CONFIG_I2C=y CONFIG_I2C_CHARDEV=y
Make sure that the appropriate I2C bus is enabled in BIOS settings: Chipset -> South Cluster Configuration -> LPSS Configuration LPSS I2C #[1-8] Support is set to ACPI mode or PCI mode Set LPSS I2C #[1-8] Speed is set to Standard Mode of Fast Mode
NB: All buses must be enabled in the range 1-7, not only I2C-7
Determine the type of the GPIO extender chip. Possible options are:
PCA9335
XRA1201
For this purpose i2cdetect utility may be used:
i2cdetect -y -r 7
PCA9335 chip should be found at address 0x27, whereas XRA1201 chip at 0x4e
Issue the following command (superuser privileges are necessary)
echo pca9535 0x27> /sys/bus/i2c/devices/i2c-7/new_device
in case pca9535 chip found
or
echo pca9535 0x4e> /sys/bus/i2c/devices/i2c-7/new_device
and check the kernel debug messages for a line like that:
i2c i2c-7: new_device: Instantiated device pca9535 at 0x27
To find the appropriate GPIO issue the command:
ls /sys/bus/i2c/drivers/pca953x/
and look the output for a line like this:
7-0027
and then issue the command:
ls /sys/class/gpio/gpiochip*/device -l
and look the output for a line like this:
/sys/class/gpio/gpiochip251/device -> ../../../7-0027
The bus number and address have to be the same in the both cases (7 and 27 in the example). Hence, the gpiochip251 is the sought; the individual GPIO line number are from 251 to 251+15
The found GPIO may be operated over sysfs interface this way:
issue the commands:
export n=251 # desired GPIO number echo $n >/sys/class/gpio/export echo out >/sys/class/gpio/gpio$n/direction # desired direction in/out cat /sys/class/gpio/gpio$n/value # read the input value echo 1 > /sys/class/gpio/gpio$n/value # write a value for output