GPIO Interrupt

How GPIO Interrupts Work

A GPIO interrupt is a hardware mechanism that detects changes in the state of a General-Purpose Input/Output (GPIO) pin and notifies the system, typically by interrupting the CPU. Instead of continuously polling the GPIO pin (which is inefficient), an interrupt allows the system to respond only when an event (such as a voltage change) occurs on the pin.

Basic Steps in a GPIO Interrupt:

1. Edge Detection: The system configures the GPIO pin to detect specific voltage transitions, such as:
   • Rising edge: When the pin’s voltage changes from low to high.
   • Falling edge: When the pin’s voltage changes from high to low.
   • Both edges: When the pin changes in either direction.
2. Interrupt Generation: When the configured edge is detected, the GPIO hardware generates an interrupt signal to the CPU.
3. Interrupt Handling: The CPU stops its current task, saves the context, and jumps to the Interrupt Service Routine (ISR), which is a predefined function to handle the event.
4. Interrupt Response: In the ISR, the specific action for the interrupt is performed, such as reading a sensor value, toggling another GPIO pin, or initiating communication over a bus.
5. Return to Main Task: Once the ISR completes, the CPU restores the previous task’s context and resumes its execution.

Steps to Determine GPIO Interrupt Capability

1. Consult the EC Chip’s Datasheet

• The datasheet for the specific EC chip (e.g., Nuvoton, Super I/O, or any other EC) will provide detailed information about the GPIO pins, including whether they can be used as interrupt sources.

• Look for sections like:

  • GPIO functions
  • Interrupt capabilities
  • Pin multiplexing (sometimes a GPIO pin can be multiplexed to serve different functions, including as an interrupt pin)

• Example: A typical section of a datasheet might say:

  GPIO 12–19 can be configured as external interrupt sources, with support for both rising and falling edge detection.

2. Check the EC Chip’s Pin Configuration and Registers

• The

  registers

  of the EC chip often provide configuration options for enabling interrupts on specific GPIO pins. Look for:

  • Interrupt Enable Register: Lists which GPIO pins can be configured as interrupt sources.
  • Interrupt Edge Configuration: Defines how the GPIO can detect interrupts (rising, falling, or both edges).

• Example register names:

  • GPIO Interrupt Mask Register (IMR)
  • Interrupt Status Register (ISR)
  • Interrupt Edge Register (IER)

These registers indicate how the GPIO pins can be configured to trigger interrupts.

3. Use the Embedded System Firmware or BIOS Settings

• If the EC chip is integrated into a system (such as a laptop or industrial device), the firmware (e.g., BIOS, UEFI, or EC firmware) might provide settings or an interface for configuring GPIO pins as interrupts.
• Use BIOS/UEFI menus or the EC’s firmware console to review and configure GPIO interrupt capabilities, depending on the platform.

4. Use Linux Sysfs (for Linux-Based Systems)

• If you are running Linux on your embedded system, you can explore available GPIO interrupts through the

  sysfs interface:

  1. List the available GPIO chips:

     ls /sys/class/gpio/

  2. Check if any GPIOs are already configured for interrupts by examining the edge attribute for each GPIO:

     cat /sys/class/gpio/gpio<GPIO_PIN_NUMBER>/edge

  3. If a GPIO can be configured as an interrupt, this file will list the possible edge settings: none, rising, falling, or both.

5. Review Platform-Specific Documents or Schematics

• In many embedded systems, the EC chip is part of a larger platform or SoC (System on Chip). You can consult:
  • Platform datasheets: These may document how many GPIOs are available and which ones can act as interrupt sources.
  • Hardware schematics: This can help determine which GPIOs are mapped to the EC and what their interrupt capabilities are.

6. Refer to EC Firmware Code (if available)

• If you have access to the EC firmware source code or configuration, check how GPIO interrupts are defined and handled in the code.
• Typically, you’ll find interrupt configurations in initialization files or GPIO configuration code that directly interfaces with the EC registers.

For example:

// Configure GPIO12 as an interrupt
GPIO_INT_ENABLE |= (1 << 12);  // Enable interrupt on GPIO12

7. Check Manufacturer Tools or Libraries

• Some manufacturers provide software tools or libraries to configure EC chips, including GPIO and interrupt settings.
• Example: If you are working with an EC chip from a manufacturer like Nuvoton, they might offer a development toolchain with utilities to configure and monitor GPIO interrupts.