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Gets the base of XIOs on C.H.I.P. computers. Currently on 4.3, it's 408, and on 4.4 it's 1016. This calculates it dynamically
import os
GPIO_PATH = "/sys/class/gpio" # The root of the GPIO directories
EXPANDER = "pcf8574a" # This is the expander that is used on CHIP for the XIOs
def get_xio_base():
Determines the base of the XIOs on the system by iterating through the /sys/class/gpio
directory and looking for the expander that is used. It then looks for the
"base" file and returns its contents as an integer
names = os.listdir(GPIO_PATH)
for name in names: # loop through child directories
prefix = GPIO_PATH + "/" + name + "/"
file_name = prefix + "label"
if os.path.isfile(file_name): # is there a label file in the directory?
with open(file_name) as label:
contents =
if contents.startswith(EXPANDER): # does label contain our expander?
file_name = prefix + "base"
with open(file_name) as base: # read the sibling file named base
contents =
return int(contents) # convert result to an int
if __name__ == '__main__':
print get_xio_base()

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@hudsantos hudsantos commented May 20, 2017

Couldn't it be simplified for those who do not want to use python, by just:

# grep -l pcf8574a $(find /sys/class/gpio/gpio*/ -maxdepth 1 -type f -name label) | grep -o "[0-9]*"

This single grep command seems to show me that the expander pcf8574a is under xio_base 1013..


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@FedericoCeratto FedericoCeratto commented Feb 27, 2018

Or better:

grep -l pcf8574a /sys/class/gpio/gpiochip*/label  | grep -o "[0-9]*"
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