Coordinating multiple real-time functions of a peripheral over a synchronous serial bus

Abstract

Time-critical actions of peripherals sharing a synchronous serial bus can be coordinated flexibly in real time by transmitting the messages through the bus well in advance of the scheduled execution time rather than 'just in time.' The messages include an action code addressed to the peripheral's shadow register and a time-to-strobe, measured in bus-clock cycles, calculated by a time protocol engine in the system controller and addressed to the peripheral's counting register. The action code is stored in the shadow register while the counting register counts up or down to the time-to-strobe using the bus-clock signal. When the count reaches zero, the action code is written to the function-control register, triggering immediate execution of the action. Because the time-to-strobe can be any number of clock cycles within the counting register's capacity, the transmission timing is decoupled from the execution timing, relaxing transmission-timing constraints.