Simple circuit for sending command upon boot to the target device sortof boostraping hardware tachnique, an app note from Analog Devices. Link here (PDF)
This application note describes the operation of a general purpose, microcontroller-based Serial Port Interface (SPI) boot circuit. This is a low cost solution for users who need to modify some of their device’s parameters at power up. This circuit addresses a 3-wire SPI application for programming converters, or any device that has a SPI option, and sends commands to user-defined SPI registers.