Prus

PRUs, short for Programmable Real-time Units, are a pair of small, deterministic microcontrollers integrated into TI Sitara processors and the PRU-ICSS subsystem. They are designed to handle time-critical input/output tasks independently of the main application processor, enabling precise waveform generation, fast bit-banging, and offloading real-time work from the host core.

Each PRU runs a simple 32-bit RISC-like instruction set with its own program and data memory. Programs are typically loaded into dedicated instruction RAM, and data can be stored in dedicated data RAM accessible to both PRUs. PRUs expose a straightforward I/O mechanism: a pair of special registers, R30 for outputs and R31 for inputs, which allow direct control of and reading from external pins. Communication with the host processor is achieved through shared memory regions (PRU-ICSS RAM) and a programmable interrupt system, enabling low-latency signaling and synchronization.

In many TI devices, the PRUs are part of the PRU-ICSS (Programmable Realtime Unit and Industrial Communication SubSystem). This setup provides two PRUs along with interfaces and controllers to support real-time control and industrial protocols. The PRUs can handle time-critical tasks such as motor control, precise PWM generation, sampling of sensors at fixed rates, and implementing custom or protocol-specific interfaces, while the main CPU manages higher-level processing and networking.

Development and deployment typically use TI’s Code Composer Studio with a PRU C compiler or other supported toolchains. Programs are loaded at boot or on demand and run without an operating system, offering deterministic timing at the cost of a more manual software workflow. Limitations include limited memory, lack of a memory protection unit, and the need for careful design to maintain timing determinism.