Difference between revisions of "Application note - GPIO on fitlet2 with FC-SCG running Linux"

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(I2C GPIO extender binding and usage)   (change visibility)
(I2C GPIO extender binding and usage)   (change visibility)
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2. Make sure that the appropriate I2C bus is enabled in BIOS settings: <br>
 
2. Make sure that the appropriate I2C bus is enabled in BIOS settings: <br>
 
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
 
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
<br>'''NOTE:''' It’s strongly recommended that All buses are enabled in the range 1-7
+
<br>'''NOTE:''' It’s strongly recommended that all buses are enabled in the range of 1-7
  
 
3.Find the GPIO extender on an I2C bus:
 
3.Find the GPIO extender on an I2C bus:
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'''Note:''' PCA9335 chip should be found at address 0x27, whereas XRA1201 chip at 0x4e
 
'''Note:''' PCA9335 chip should be found at address 0x27, whereas XRA1201 chip at 0x4e
  
 
+
4. Bind the above found device to driver (superuser privileges are necessary)
4. Bind the above found device to driver (superuser privileges are necessary)
+
 
  echo pca9535 $busaddr >/sys/bus/i2c/devices/i2c-${busnum}/new_device  
 
  echo pca9535 $busaddr >/sys/bus/i2c/devices/i2c-${busnum}/new_device  
and check the kernel debug messages for a line like that:
+
Then check the kernel debug messages for a line like the following:
 
  i2c i2c-7: new_device: Instantiated device pca9535 at 0x27
 
  i2c i2c-7: new_device: Instantiated device pca9535 at 0x27
  
5. To find the appropriate GPIO issue the command:
+
5. To find the appropriate GPIO, issue the command:
 
  ls /sys/bus/i2c/drivers/pca953x/
 
  ls /sys/bus/i2c/drivers/pca953x/
and look the output for a line like this:
+
Then look the output for a line like:
 
  7-0027
 
  7-0027
and then issue the command:
+
And then issue the command:
 
  ls /sys/class/gpio/gpiochip*/device -l
 
  ls /sys/class/gpio/gpiochip*/device -l
and look the output for a line like this:
+
Afterwards, look at the output for a line like the following:
 
  /sys/class/gpio/gpiochip251/device -> ../../../7-0027
 
  /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).  
+
The bus number and address has to be the same in 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
+
Hence, the gpiochip251 is to be sought; the individual GPIO line number are from 251 to 251+15
  
 
+
6. The GPIO found may be operated over sysfs interface in the following way:  
 
+
6. The found GPIO may be operated over sysfs interface in the following way:  
+
 
issue the commands:
 
issue the commands:
 
  export n=251 # desired GPIO number
 
  export n=251 # desired GPIO number
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  cat /sys/class/gpio/gpio$n/value # read the input value
 
  cat /sys/class/gpio/gpio$n/value # read the input value
 
  echo 1 > /sys/class/gpio/gpio$n/value # write a value for output
 
  echo 1 > /sys/class/gpio/gpio$n/value # write a value for output
 
  
  

Revision as of 10:42, 5 March 2019

  • This application note applies to fitlet2 with FC-SCG FACET-Card running Linux.
  • It provides an example of how to use the supported I2C GPIO extender feature of FC-SCG under Linux.

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

2. 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
NOTE: It’s strongly recommended that all buses are enabled in the range of 1-7

3.Find the GPIO extender on an I2C bus:

readonly dev_func='17.2' 
busnum=$(ls -l /sys/bus/i2c/devices/ | sed -ne 
"/${dev_func}\/i2c_designware/ s/^.*i2c-\(digit:\{1,2\}\)$/\1/p") 
busaddr=$(i2cdetect -y -r $busnum | sed -ne 
's/^.*\(\(27\|4e\)\).*$/0x\1/Ip') 
busaddr=$((busaddr)) 
printf "Device found @ 0x%x on bus %i\n" $busaddr $busnum 

Note: PCA9335 chip should be found at address 0x27, whereas XRA1201 chip at 0x4e

4. Bind the above found device to driver (superuser privileges are necessary)

echo pca9535 $busaddr >/sys/bus/i2c/devices/i2c-${busnum}/new_device 

Then check the kernel debug messages for a line like the following:

i2c i2c-7: new_device: Instantiated device pca9535 at 0x27

5. To find the appropriate GPIO, issue the command:

ls /sys/bus/i2c/drivers/pca953x/

Then look the output for a line like:

7-0027

And then issue the command:

ls /sys/class/gpio/gpiochip*/device -l

Afterwards, look at the output for a line like the following:

/sys/class/gpio/gpiochip251/device -> ../../../7-0027

The bus number and address has to be the same in both cases (7 and 27 in the example). Hence, the gpiochip251 is to be sought; the individual GPIO line number are from 251 to 251+15

6. The GPIO found may be operated over sysfs interface in the following 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