PRU software support makes for easy real-time programming

7th November 2014

Barney Scott

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Whitepaper

The Programmable Real-time Unit (PRU) on Texas Instruments' Sitara processors enables customers to differentiate their products by offloading real-time processing from the ARM core. A 200MHz low-latency multicore co-processor, the PRU is optimised for deterministic, real-time processing, with local peripherals and memory which allows customers to save time and money by removing costly FPGAs or ASICs from system designs.

The PRU offloads processing from the ARM core in order to manage deterministic tasks such as time-critical I/O manipulation. It is robust enough to enable complex functions like motor control in applications such as 3D printers, LED lighting control, robotics, thermal printing.

The nature of the PRU, along with its single-cycle direct access to I/O pins within 5ns and SoC resources, allows flexibility in implementing fast real-time responses, specialised data handling operations, custom peripheral interfaces and offloading tasks from the SoC's other processor cores. It also enables developers to implement different interfaces including bit-banging serial interfaces like I2C and SPI, advanced PWMs, motor control, RS485, sample rate conversion and sensor monitoring.

TI offers a comprehensive PRU software support package, providing a framework and examples for software development. The package contains example PRU firmware, demonstrating the PRU capabilities in order to interact with and control the system and its resources, as well as application loader code for the host OS. The recently released C compiler, as part of the Code Composer Studio integrated development environment v6, makes PRU programming easier and eliminates the need for assembly level programming as developers can debug over JTAG.

The PRU cape plug-in board, sold and supported by TI, is an addition to capes available from the community for the BeagleBone Black. It gives customers an inexpensive way to evaluate the PRU capabilities on Sitara processors. The PRU cape allows easy evaluation and learning to programme the dual-core PRU in AM335x processors. It also provides access to a variety of features, including basic general purpose output via seven LEDs, general purpose input via two push buttons, simple audio, UART, HDQ temperature sensor, GPIO header and a proto board area. The code is reusable in other Sitara processor families such as the AM437x solutions, which include a more feature rich, quad-core PRU.