Colin Walls has over thirty years experience in the electronics industry, largely dedicated to embedded software. A frequent presenter at conferences and seminars and author of numerous technical articles and two books on embedded software, Colin is an embedded software technologist with Mentor … More »
Measurement of interrupt latency
December 19th, 2017 by Colin Walls
The term “interrupt latency” is widely used, but, like a lot of technical terms, its meaning is sometimes unclear. This is our first challenge – to define our terms. The second challenge is to make a meaningful measurement.
Most RTOS vendors quote interrupt latency figures for their products. However, they may be referring to either one of two time intervals. In both cases, they are talking about the delay before an interrupt is serviced, but there are two ways to see this:
Figures quoted by RTOS vendors may be useful, once the terminology is figured out, but remember the figure is dependent on a number of factors which may not align with your system design:
Clearly it might be more useful to make the measurement yourself.
To measure short time intervals in any electronic system, you need an instrument. And the best tool for this kind of job is an oscilloscope. One approach is to use one pin on a GPIO interface to generate the interrupt. This pin can be monitored on the ‘scope. At the start of the interrupt service routine, another pin, which is also being monitored, is toggled. The interval between the two signals may be easily read from the instrument.
I can imagine that a software engineer may be appalled by the thought of using an oscilloscope, but this might be an ideal opportunity to liaise with your hardware design counterpart. Actually, such liaison might be a good idea anyway …