Improving ModBus Extension performance using PRU unit from Sitara AM335x

Abstract

Local industrial networks represent a model with only three levels physical, data link, and application for use in the domain of the industrial processes using computing elements with low resources of type microcontroller. Modbus is a simple and easy to implement protocol but partially defined from the point of view of devices determinism and functionality described in the network. Modbus Extension completes the Modbus by defining some Modus compatible messages of an acquisition cycle and a device description mode. To implement the acquisition cycle the best possible implementation in using a communication channel was pursued, in conditions that the serial communication speeds of modern microcontrollers have reached up to 27Mb/s. At this speed, any over-control given by real-time operating systems or interrupt handling routines creates significant times in the structure of an acquisition cycle. The paper presents an implementation solution using the PRUs from Sitara AM335x, which at a speed of 12 Mb/s, a 75.53% percentage of channel usage for payload data was obtained.