GPIOCP: Timing-Accurate General Purpose I/O Controller for Many-core Real-time Systems

Zhe Jianga and Neil C. Audsleyb
Department of Computer Science, University of York, York, UK.


Modern SoC / NoC chips often provide General- Purpose I/O (GPIO) pins for connecting devices that are not directly integrated within the chip. Timing accurate control of devices connected to GPIO is often required within embedded real-time systems - ie. I/O operations should occur at exact times, with minimal error, neither being significantly early or late. This is difficult to achieve due to the latencies and contentions present in architecture, between CPU instigating the I/O operation, and the device connected to the GPIO - software drivers, RTOS, buses and bus contentions all introduce significant variable latencies before the command reaches the device. This is compounded in NoC devices utilising a mesh interconnect between CPUs and I/O devices.
The contribution of this paper is a resource efficient programmable I/O controller, termed the GPIO Command Processor (GPIOCP), that permits applications to instigate complex sequences of I/O operations at an exact time, so achieving timing-accuracy at a single clock cycle level. Also, I/O operations can be programmed to occur at some point in the future, periodically, or reactively. The GPIOCP is a parallel I/O controller, supporting cycle level timing accuracy across several devices connected to GPIO simultaneously.
The GPIOCP exploits the tradeoff between placing using a full sequential CPU to control each GPIO connected device, which achieves some timing accuracy at high resource cost; and poor timing-accuracy achieved where the application CPU controls the device remotely. The GPIOCP has efficient hardware cost compared to CPU approaches, with the additional benefits of total timing accuracy (CPU solutions do not provide this in general) and parallel control of many I/O devices.

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