This is a preview version of the DisplayLink DL-7450 Software Development Kit Documentation. The functionality that is described and made available in this version is subject to addition, removal or change without warning.

gpio — General-Purpose Input/Output Pin Management

Most microcontrollers offer some General-Purpose Input/Output (GPIO) pins for providing application functionality. GPIO pins can be used to detect digital signal inputs or to emit digital output signals and are controlled by software. A digital input pin is used for detecting signals from buttons and sensors, while digital output pins can be used, for example, to light an LED. This module provides DL-7450 application developers with an API for building docking stations that have enhanced functionality using GPIO pins.

Docking station designers may wish to incorporate functionality that uses GPIO pins. The DL-7450 has 16 built-in GPIOs, each of which can be configured via the DisplayLink firmware web builder. The functionality for these native GPIO pins is limited. However, there are up to four I2C Input/Output expanders available via the DL-7450 SDK. Each of them supports up to eight digital input or output pins. To make these GPIOs constrollable using the SDK, the expander must be wired to the the I2C1 bus. Refer to DL-12xx, DL-25xx and DL-7xx Design Guidelines for a description. For example, the Redwood reference design has an NXP PCA9538A I/O expander connected to the i2c1 bus at address 0x72. The pins should be named in the configuration that is programmed into the dock in the factory process. This abstracts the hardware implementation, so that application code can be ported across different board designs. It also provides the means for integrity checks in application code.

A example showing how a joystick can be incorporated into a Redwood reference design is provided in the sample code.

Functions

gpio.create(pin_name, callback=None)

Create a suitable control object based on the GPIO name defined for the board. This function will return either a DigitalInput or DigitalOutput object.

The parameters are:

• pin_name the custom name of the GPIO pin, as defined in the manufacturing process for the board. If the pin name is not defined by the board configuration, a TypeError exception is raised.

• callback (optional). For pins which are configured as digital inputs, a callback may be provided. The callback is any Python callable entity which takes no parameters. Any return value is ignored. Providing a callback for a pin that is configured as a digital output will result in a TypeError exception being raised.

Classes

• class DigitalInput – manage a GPIO configured as a digital input
• class DigitalOutput – manage a GPIO configured as a digital output