134 lines
3.7 KiB
Markdown
134 lines
3.7 KiB
Markdown
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## User Accessible GPIOs (J12)
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Helios4 provides 12 GPIOs on header J12 which can be used for user application. Those GPIOs are provided via an 16-bit IO Expander [PCA9655E](http://www.onsemi.com/PowerSolutions/product.do?id=PCA9655E) connected to I2C bus 0.
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### Pinout Table
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| Pin | Port | Remarks |
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|------------|----------|---------|
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| 1 | - | 3.3V supply |
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| 2 | IO0_2 | |
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| 3 | IO0_3 | |
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| 4 | IO0_4 | |
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| 5 | IO0_7 | |
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| 6 | IO1_0 | |
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| 7 | IO1_1 | |
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| 8 | IO1_2 | |
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| 9 | IO1_3 | |
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| 10 | IO1_4 | |
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| 11 | IO1_5 | |
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| 12 | IO1_6 | |
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| 13 | IO1_7 | |
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| 14 | - | GND |
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!!! warning
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Ports **IO0_0**, **IO0_1**, **IO0_5**, and **IO0_6** are reserved for system use.
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!!! important
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It is not advisable to access the I2C IO Expander directly using I2C utilities.
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## Accessing GPIOs under Linux
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If the kernel supports debugfs (*CONFIG_DEBUG_FS=y*), list of GPIOs can be retrieved with the following command
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```bash
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sudo cat /sys/kernel/debug/gpio
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```
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Look for the **gpiochip2: GPIOs XXX-YYY** section, whereas **XXX** is first GPIO number and **YYY** is last GPIO number of IO expander.
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```
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gpiochip2: GPIOs 496-511, parent: i2c/0-0020, pca9555, can sleep:
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gpio-496 ( |board-rev-0 ) in lo
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gpio-497 ( |board-rev-1 ) in lo
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gpio-498 ( |(null) ) out hi
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gpio-499 ( |(null) ) in hi
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gpio-500 ( |(null) ) in hi
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gpio-501 ( |usb-overcurrent-stat) in hi
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gpio-502 ( |USB-PWR ) out hi
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gpio-503 ( |(null) ) in hi
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gpio-504 ( |(null) ) in hi
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gpio-505 ( |(null) ) in hi
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gpio-506 ( |(null) ) in hi
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gpio-507 ( |(null) ) in hi
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gpio-508 ( |(null) ) in hi
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gpio-509 ( |(null) ) in hi
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gpio-510 ( |(null) ) in hi
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gpio-511 ( |(null) ) in hi
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```
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Another way to get first GPIO number of the IO expander
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```
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cat /sys/bus/i2c/devices/0-0020/gpio/gpiochip*/base
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```
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Therefore the mapping between header J12 Pins and Sysfs GPIO numbers will be as described in the following table
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### GPIO Table
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| Pin | Sysfs GPIO number | Remarks |
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|----|-----|---------|
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| 1 | - | 3.3V supply |
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| 2 | 498 | |
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| 3 | 499 | |
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| 4 | 500 | |
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| 5 | 503 | |
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| 6 | 504 | |
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| 7 | 505 | |
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| 8 | 506 | |
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| 9 | 507 | |
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| 10 | 508 | |
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| 11 | 509 | |
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| 12 | 510 | |
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| 13 | 511 | |
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| 14 | - | GND |
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!!! note
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The mapping table is unlikely to change between Kernel version.
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### GPIO Control
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**1.** Export the GPIO number you want to use
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```
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echo N | sudo tee -a /sys/class/gpio/export
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```
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**2.** Set the direction, "out" for Output or "in" for Input
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```
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echo DIRECTION | sudo tee -a /sys/class/gpio/gpioN/direction
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```
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**3.** Now you can read or change the GPIO value
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To read GPIO value
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```
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cat /sys/class/gpio/gpioN/value
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```
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To change GPIO value (only if GPIO set as Output)
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```
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echo VALUE | sudo tee -a /sys/class/gpio/gpioN/value
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```
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!!! notes
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Pay attention to the path, /sys/class/gpio/gpio**N**/ where **N** is the GPIO number.
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#### Example
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Set IO1_7 (pin 13) output as high
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```
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echo 511 | sudo tee -a /sys/class/gpio/export
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echo "out" | sudo tee -a /sys/class/gpio/gpio511/direction
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echo 1 | sudo tee -a /sys/class/gpio/gpio511/value
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```
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