Reset GPIO pins

GPIO expanders

for GPIO pins to connect multiple i2c devices when the number of available on board pins are less

/RESET

in schematics means active low

GPIO - General Purpose Input Output

• They are General Purpose Input Output and are pins on various processors that aren’t dedicated to anything.

As a recap, each gpio pin on the BBB has three different numbering schemes associated with it!

1. The physical pin location, in the form of PX_Y (P8_28)
2. The gpio name, in the form of GPIOX_Y (GPIO2_24)
3. The gpio number, in the form of $$32*X + Y (88)$$

The Pi’s GPIO ports can be controlled from the command line (i.e. bash), python scripts, and C/C++ programs. There are 17 GPIO ports available on the Pi. Some of them have special purposes or special hardware configurations and should be avoided for normal use.

#   Exports pin to userspace
echo "18" > /sys/class/gpio/export

# Sets pin 18 as an output
echo "out" > /sys/class/gpio/gpio18/direction

# Sets pin 18 to high
echo "1" > /sys/class/gpio/gpio18/value

# Sets pin 18 to low
echo "0" > /sys/class/gpio/gpio18/value

How to Reset a sensor via GPIO pin?

Find the sensor register (GPIO Expander)

1. Find on FS by register name
2. 456 appears to be the first Pin

3. Need second pin from IO Expander

   # RESET ADC /KMD_RESET
   cd /sys/class/gpio
   echo 457 > export
   sleep 1
   cd gpio457
   find . -maxdepth 1 -type f -exec head {} +
   echo out > direction
   echo 1 > value
   sleep 1
   spidev_test --device /dev/spidev0.0 --verbose --cpha --speed 1000000 -p '\x10\x00'
   echo 0 > value
   find . -maxdepth 1 -type f -exec head {} +
   spidev_test --device /dev/spidev0.0 --verbose --cpha --speed 1000000 -p '\x10\x00'
   cd ..
   echo 457 > unexport
   

Questions

• What is the difference between GPIO pin and GPIOchip? *

Footnotes

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