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

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  CONFIG_I2C_CHARDEV=y
 
  CONFIG_I2C_CHARDEV=y
  
2. Make sure that the appropriate I2C bus is enabled in BIOS settings:
+
2. Make sure that the appropriate I2C bus is enabled in BIOS settings: <br>
Chipset -> South Cluster Configuration -> LPSS Configuration
+
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
'''LPSS I2C #[1-8]''' Support is set to '''ACPI mode or PCI mode
+
'''NOTE:''' It’s strongly recommended that All buses are enabled in the range 1-7
Set LPSS I2C #[1-8] Speed''' is set to '''Standard Mode''' of '''Fast Mode'''
+
  
'''NOTE:''' All buses must be enabled in the range 1-7, not only I2C-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))
  
3. Determine the type of the GPIO extender chip. Possible options are:
+
printf "Device found @ 0x%x on bus %i\n" $busaddr $busnum
  
* PCA9335
+
'''Note:''' PCA9335 chip should be found at address 0x27, whereas XRA1201 chip at 0x4e
* 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
 
 
 
4. 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
 
  
 +
4. Bind  the above found device to driver (superuser privileges are necessary)
 +
echo pca9535 $busaddr >/sys/bus/i2c/devices/i2c-${busnum}/new_device
 
and check the kernel debug messages for a line like that:
 
and check the kernel debug messages for a line like that:
 
+
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:
 
and look the output for a line like this:
 
+
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:
 
and look the output for a line like this:
 +
/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 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
 
Hence, the gpiochip251 is the sought; the individual GPIO line number are from 251 to 251+15
  
  
6. The found GPIO may be operated over sysfs interface in the following way:
 
<br>issue the commands:
 
  
 +
6. The found GPIO may be operated over sysfs interface in the following way:
 +
issue the commands:
 
  export n=251 # desired GPIO number
 
  export n=251 # desired GPIO number
 
  echo $n >/sys/class/gpio/export
 
  echo $n >/sys/class/gpio/export
Line 72: Line 55:
 
  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 10:35, 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 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 

and check the kernel debug messages for a line like that:

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/

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


6. The found GPIO 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