In software, you pass configuration on the command line or in environment variables. In hardware, you "strap" pins to a particular value when the chip powers o

In software, you pass configuration on the command line or in environment variables. In hardware, you "strap" pins to a particular value when the chip powers on. You can strap them high (tie them to the power source), strap them low (tie them to GND), or sometimes they do something fancier and tie them high or low via a particular resistor (for more fine-grained configurations like timing patterns, power selection, or I2C address selection in pin-constrained environments). Usually you can reuse the pins for something else after power on. Often there are efuse bits you can blow after manufacture in order to override the strapping values and use the pins as normal IOs.