Mastering Embedded Linux Programming - Second Edition

GPIO

General-Purpose Input/Output (GPIO) is the simplest form of digital interface since it gives you direct access to individual hardware pins, each of which can be in one of two states: either high or low. In most cases you can configure the GPIO pin to be either an input or an output. You can even use a group of GPIO pins to create higher level interfaces such as I²C or SPI by manipulating each bit in software, a technique that is called bit banging. The main limitation is the speed and accuracy of the software loops and the number of CPU cycles you want to dedicate to them. Generally speaking, it is hard to achieve timer accuracy better than a millisecond unless you configure a real-time kernel, as we shall see in Chapter 16, Real-Time ...