# GPIO Control

The ARK Just a Jetson Carrier includes an I2S0 connector that can be reconfigured as general-purpose GPIOs using a device tree overlay.

## I2S0 Connector Pin Mapping

| ARK Pin | ARK Signal       | 40-Pin Header | Pinmux Name |
| ------- | ---------------- | ------------- | ----------- |
| 1       | VDD\_5V\_JPERIPH | -             | -           |
| 2       | I2S0\_DOUT\_3V3  | Pin 40        | I2S0\_DOUT  |
| 3       | I2S0\_DIN\_3V3   | Pin 38        | I2S0\_DIN   |
| 4       | I2S0\_LRCLK\_3V3 | Pin 35        | I2S0\_FS    |
| 5       | I2S0\_SCLK\_3V3  | Pin 12        | I2S0\_SCLK  |
| 6       | AUD\_MCLK\_3V3   | Pin 7         | GPIO09      |
| 7       | GND              | -             | -           |

## Enabling the GPIO Overlay

The I2S pins are configured for I2S audio by default. To use them as GPIOs, you need to apply the "ARK I2S to GPIO" overlay using jetson-io.

```
sudo /opt/nvidia/jetson-io/config-by-hardware.py -n "ARK I2S to GPIO"
sudo reboot
```

## Using the GPIOs

First, install `Jetson.GPIO` 2.1.12 or newer — the apt-shipped version doesn't recognize the Orin Nano Super and will fail with `Could not determine Jetson model`:

```bash
sudo pip3 install 'Jetson.GPIO>=2.1.12'
```

After applying the overlay and rebooting, you can control the pins using the Jetson.GPIO Python library. The pins are addressed by their 40-pin header number. The example below jumpers HDR40 pin 40 (DOUT) to pin 38 (DIN) and toggles HIGH/LOW/HIGH/LOW, reading each transition back as a loopback test.

```python
import time
import Jetson.GPIO as GPIO

GPIO.setmode(GPIO.BOARD)
GPIO.setup(40, GPIO.OUT, initial=GPIO.LOW)  # I2S0_DOUT
GPIO.setup(38, GPIO.IN)                     # I2S0_DIN

try:
    for level in (GPIO.HIGH, GPIO.LOW, GPIO.HIGH, GPIO.LOW):
        GPIO.output(40, level)
        time.sleep(0.2)
        got = GPIO.input(38)
        label = "HIGH" if level else "LOW"
        result = "PASS" if got == level else f"FAIL (read {got})"
        print(f"DOUT=40 {label}  DIN=38 {got}  {result}")
finally:
    GPIO.cleanup()
```

For a complete working example, see the [i2s\_gpio\_example.py](https://github.com/ARK-Electronics/ARK-OS/blob/main/platform/jetson/scripts/i2s_gpio_example.py) script in ARK-OS.

## Creating Custom Overlays

To create your own overlay for different pins, refer to the annotated example overlay in the [ark\_jetson\_kernel](https://github.com/ARK-Electronics/ark_jetson_kernel/blob/main/device_tree/ark_jaj/Linux_for_Tegra/source/hardware/nvidia/t23x/nv-public/overlay/ark_i2s_gpio.dts) repository.

The overlay file contains documentation explaining how to:

1. Find your connector's signals in the carrier board schematic
2. Map signals to 40-pin header pins using the Jetson Pinmux Spreadsheet
3. Look up SoC GPIO names in the GPIO header file
4. Configure pin properties (tristate, input enable, pull resistors)

For more information on Jetson device tree overlays, see the [NVIDIA Jetson-IO Documentation](https://docs.nvidia.com/jetson/archives/r36.4/DeveloperGuide/HR/ConfiguringTheJetsonExpansionHeaders.html).

{% hint style="warning" %}
**GPIO state after script exit**

On ARK Jetson Carriers, the I2S→GPIO pins come up driven LOW at boot (programmed by MB1 BCT). While your app owns the line, the kernel guarantees its value. **On release (clean exit, crash, or kill), the pin retains its last-written value** until the next reboot, when the BCT default re-asserts. If your app drives a relay HIGH and crashes, the relay stays HIGH until reboot.

If you need a different default — active-low actuator, peripheral reset that must release on boot, etc. — see the [ARK Jetson Kernel GPIO docs](https://github.com/ARK-Electronics/ark_jetson_kernel/blob/main/docs/gpio.md#safe-state-when-no-app-owns-the-pin) for safe-state patterns (external pull resistors, `gpio-hog`, signal-mode daemons). For `gpioset` from a shell, use `--mode=signal` to keep the process alive and explicitly own the line.
{% endhint %}


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