
## User Accessible GPIOs (J12)

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.

![J12 Pinout](/img/gpio/gpio_pinout_j12.png)

### Pinout Table

| Pin | Port | Remarks |
|------------|----------|---------|
| 1 |    -   |   3.3V supply  |
| 2 | IO0_2  |    |
| 3 | IO0_3  |    |
| 4 | IO0_4  |    |
| 5 | IO0_7  |    |
| 6 | IO1_0  |    |
| 7 | IO1_1  |    |
| 8 | IO1_2  |    |
| 9 | IO1_3  |    |
| 10 | IO1_4  |    |
| 11 | IO1_5  |    |
| 12 | IO1_6  |    |
| 13 | IO1_7  |    |
| 14 |   -    | GND |

!!! warning
    Ports **IO0_0**, **IO0_1**, **IO0_5**, and **IO0_6** are reserved for system use.

!!! important
    It is not advisable to access the I2C IO Expander directly using I2C utilities.

## Accessing GPIOs under Linux

If the kernel supports debugfs (*CONFIG_DEBUG_FS=y*), list of GPIOs can be retrieved with the following command

```bash
sudo cat /sys/kernel/debug/gpio
```

Look for the **gpiochip2: GPIOs XXX-YYY** section, whereas **XXX** is first GPIO number and **YYY** is last GPIO number of IO expander.


```
gpiochip2: GPIOs 496-511, parent: i2c/0-0020, pca9555, can sleep:
 gpio-496 (                    |board-rev-0         ) in  lo    
 gpio-497 (                    |board-rev-1         ) in  lo    
 gpio-498 (                    |(null)              ) out hi    
 gpio-499 (                    |(null)              ) in  hi    
 gpio-500 (                    |(null)              ) in  hi    
 gpio-501 (                    |usb-overcurrent-stat) in  hi    
 gpio-502 (                    |USB-PWR             ) out hi    
 gpio-503 (                    |(null)              ) in  hi    
 gpio-504 (                    |(null)              ) in  hi    
 gpio-505 (                    |(null)              ) in  hi    
 gpio-506 (                    |(null)              ) in  hi    
 gpio-507 (                    |(null)              ) in  hi    
 gpio-508 (                    |(null)              ) in  hi    
 gpio-509 (                    |(null)              ) in  hi    
 gpio-510 (                    |(null)              ) in  hi    
 gpio-511 (                    |(null)              ) in  hi    
```

Another way to get first GPIO number of the IO expander

```
cat /sys/bus/i2c/devices/0-0020/gpio/gpiochip*/base
```

Therefore the mapping between header J12 Pins and Sysfs GPIO numbers will be as described in the following table

### GPIO Table

| Pin | Sysfs GPIO number | Remarks |
|----|-----|---------|
|  1 |  -  |   3.3V supply  |
|  2 | 498 |    |
|  3 | 499 |    |
|  4 | 500 |    |
|  5 | 503 |    |
|  6 | 504 |    |
|  7 | 505 |    |
|  8 | 506 |    |
|  9 | 507 |    |
| 10 | 508 |    |
| 11 | 509 |    |
| 12 | 510 |    |
| 13 | 511 |    |
| 14 |  -  |  GND |

!!! note
    The mapping table is unlikely to change between Kernel version.


### GPIO Control

**1.** Export the GPIO number you want to use

```
echo N | sudo tee -a /sys/class/gpio/export
```

**2.** Set the direction, "out" for Output or "in" for Input

```
echo DIRECTION | sudo tee -a /sys/class/gpio/gpioN/direction
```

**3.** Now you can read or change the GPIO value

To read GPIO value

```
cat /sys/class/gpio/gpioN/value
```

To change GPIO value (only if GPIO set as Output)

```
echo VALUE | sudo tee -a /sys/class/gpio/gpioN/value
```

!!! notes
    Pay attention to the path, /sys/class/gpio/gpio**N**/ where **N** is the GPIO number.

#### Example

Set IO1_7 (pin 13) output as high

```
echo 511 | sudo tee -a /sys/class/gpio/export
echo "out" | sudo tee -a /sys/class/gpio/gpio511/direction
echo 1 | sudo tee -a /sys/class/gpio/gpio511/value
```

## Use GPIO with Device Tree Overlay

!!! info
    Device Tree Compiler (dtc) from OS package manager usually is too old, use the one from kernel source or download binary version for Arm [here](/files/dt-overlay/dtc).

Another way to use the GPIO is by using device tree. In device tree the user accessible
GPIO is labelled as [expander0](https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/arch/arm/boot/dts/armada-388-helios4.dts#n155).

Instead of directly modifying the Helios4 device tree source (*armada-388-helios4.dts*) and recompiling,
Linux and U-Boot provide a mechanism called device tree overlay. With overlay, user just needs
to create simple device tree that would be overlay'd on top of base device tree.

For example, to use **IO0_2** as power off button input, create following device tree source
and save it as power-button.dts

```
/dts-v1/;
/plugin/;

/ {
	fragment@0 {
		target-path = "/gpio-keys";
		__overlay__ {
			power-button {
				label = "Soft Power Off";
				linux,code = <116>;
				gpios = <&expander0 2 1>;
			};
		};
	};
};

```
Download dtc and compile device tree with this command

```
wget https://wiki.kobol.io/files/dt-overlay/dtc
chmod 755 dtc
./dtc -I dts -O dtb -o power-button.dtbo power-button.dts
```

***Button Wiring***

![button wiring](/img/gpio/power_button_sch.png)

The GPIO has internal pull up resistor, when the button is not pressed the input read as High and when the button is pressed the input read as Low, therefore we use active low flag.

----

In the above example you will find the 2 following lines

```
linux,code = <116>;
gpios = <&expander0 2 1>;
```

For **linux,code** property, you can use one of the following values. For complete even code list refer to [input-event-codes.h](https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/plain/include/uapi/linux/input-event-codes.h).

| Event Code Name | Event Code | Description |
|-------------|-------|---------------|
| KEY_POWER   | 116   | Power Button  |
| KEY_SLEEP   | 142   | Sleep Button  |
| KEY_WAKEUP  | 116   | Power Button  |
| BTN_0       | 0x100 | User Button 0 |
| BTN_1       | 0x101 | User Button 1 |
| BTN_2       | 0x102 | User Button 2 |
| BTN_3       | 0x103 | User Button 3 |
| BTN_4       | 0x104 | User Button 4 |
| BTN_5       | 0x105 | User Button 5 |
| BTN_6       | 0x106 | User Button 6 |
| BTN_7       | 0x107 | User Button 7 |
| BTN_8       | 0x108 | User Button 8 |
| BTN_9       | 0x109 | User Button 9 |

For **gpios** properties, the syntax is as follow

`<&expander0 index flag>`

Where *index* is one of the following values

| Port Number | Index |
|-------|----|
| IO0_2 |  2 |
| IO0_3 |  3 |
| IO0_4 |  4 |
| IO0_7 |  7 |
| IO1_0 |  8 |
| IO1_1 |  9 |
| IO1_2 | 10 |
| IO1_3 | 11 |
| IO1_4 | 12 |
| IO1_5 | 13 |
| IO1_6 | 14 |
| IO1_7 | 15 |

And *flag* is one of the following values

| Flag |  Property |
|------|-----------|
| 0 | GPIO line is active high |
| 1 | GPIO line is active low |

For more info please refer to
[gpio-keys binding](https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/plain/Documentation/devicetree/bindings/input/gpio-keys.txt).

### Device Tree Overlay under Armbian

!!! info
    Armbian older than version 5.98 is still not compiled with overlay support. Refer to instruction to [Compile Helios4 DTB with Symbol Support](#compile-helios4-dtb-with-symbol-support)
    or use precompiled binary.

    Armbian Default (Stretch, Linux Kernel 4.14):

    `wget https://wiki.kobol.io/files/dt-overlay/lk4.14_armada-388-helios4.dtb`

    `sudo cp lk4.14_armada-388-helios4.dtb /boot/dtb/armada-388-helios4.dtb`

    Armbian Next (Buster, Linux Kernel 4.19):

    `wget https://wiki.kobol.io/files/dt-overlay/lk4.19_armada-388-helios4.dtb`

    `sudo cp lk4.19_armada-388-helios4.dtb /boot/dtb/armada-388-helios4.dtb`


Create */boot/overlay-user/* to store the overlay and copy the overlay to the folder

```
sudo mkdir -p /boot/overlay-user
sudo cp power-button.dtbo /boot/overlay-user/
```

Then edit */boot/armbianEnv.txt* and append the overlay filename (without dtbo extension) to *user_overlays*

`user_overlays=power-button`

Reboot the system to load the overlay.


!!! notes
    If there is more than one overlay file, separate it by space. For example

    `user_overlays=power-button sleep-button`

----

***Additional Steps for U-Boot 2018.11 (Armbian Default)***

Bootscript (**boot.scr**) used in Armbian Default does not have routine to automatically load overlay from */boot/overlay-user* therefore **/boot/boot.cmd** need to be modified.

Append the following block

```
fdt addr ${fdt_addr}
fdt resize 65536

for overlay_file in ${user_overlays}; do
	if load ${boot_interface} 0:1 ${loadaddr} ${prefix}overlay-user/${overlay_file}.dtbo; then
		echo "Applying user provided DT overlay ${overlay_file}.dtbo"
		fdt apply ${loadaddr} || setenv overlay_error "true"
	fi
done

if test "${overlay_error}" = "true"; then
	echo "Error applying DT overlays, restoring original DT"
	load ${boot_interface} 0:1 ${fdt_addr} ${prefix}dtb/${fdtfile}
fi
```

before

`bootz ${kernel_addr_r} ${ramdisk_addr_r} ${fdt_addr}`

so it become

```
fdt addr ${fdt_addr}
fdt resize 65536

for overlay_file in ${user_overlays}; do
	if load ${boot_interface} 0:1 ${loadaddr} ${prefix}overlay-user/${overlay_file}.dtbo; then
		echo "Applying user provided DT overlay ${overlay_file}.dtbo"
		fdt apply ${loadaddr} || setenv overlay_error "true"
	fi
done

if test "${overlay_error}" = "true"; then
	echo "Error applying DT overlays, restoring original DT"
	load ${boot_interface} 0:1 ${fdt_addr} ${prefix}dtb/${fdtfile}
fi

bootz ${kernel_addr_r} ${ramdisk_addr_r} ${fdt_addr}
```

Recompile with

`mkimage -C none -A arm -T script -d /boot/boot.cmd /boot/boot.scr`

----

### Device Tree Overlay under Other Distro

#### Compile Helios4 DTB with Symbol Support

Download Linux Kernel source code and extract it to *~/src/linux*. Change directory to *~/src/linux*

Download and apply kernel patch for

- Linux Kernel 4.14

```
wget https://wiki.kobol.io/files/dt-overlay/compile-dtb-lk-4.14.patch
git apply --apply compile-dtb-lk-4.14.patch
```

- Linux Kernel 4.19

```
wget https://wiki.kobol.io/files/dt-overlay/compile-dtb-lk-4.19.patch
git apply --apply compile-dtb-lk-4.19.patch
```

Compile Helios4 device tree

`make armada-388-helios4.dtb`

Copy the dtb to boot folder (eg. /boot/dtb/)

`sudo cp arch/arm/boot/dts/armada-388-helios4.dtb /boot/dtb/`

Copy the overlay also to the same folder.

#### Apply overlay on U-Boot

To apply overlay to base dtb, the procedure is

1. Load Helios4 dtb to memory
2. Set fdt address to dtb address
3. Resize the fdt
4. Load overlay to memory
5. Apply from overlay address
6. Boot the kernel

Example command

```
load mmc 0:1 ${ramdisk_addr_r} /boot/uInitrd
load mmc 0:1 ${kernel_addr_r} /boot/zImage

load mmc 0:1 ${fdt_addr_r} /boot/dtb/${fdtfile}
fdt addr ${fdt_addr_r}
fdt resize 65536
load mmc 0:1 0x300000 /boot/dtb/power-button.dtbo
fdt apply 0x300000

bootz ${kernel_addr_r} ${ramdisk_addr_r} ${fdt_addr_r}

```
