A new RTOS trace tool

January 08, 2013

Jack Ganssle-January 08, 2013

It's tough to see what's going on when in an RTOS. A new tool helps.

In a recent debate, one that mirrors so many similar discussions over the decades, a couple of smart developers vehemently objected to using an RTOS in most systems. Their complaint is valid; an RTOS brings in plenty of chances for unexpected system behavior. Scheduling isn't deterministic (using the most common approaches) and locks and priority problems can cause system hangs. But any abstraction has its own headaches. The use of an RTOS requires a new level of developer competence and use of different tools. I find that an operating system, despite the potential problems, can greatly improve a lot of systems.

The RTOS is particularly problematic as it's really tough to see what is going on. But most vendors have visualization tools. Examples include TraceX from Express Logic and µC/Probe from Micriµm. In this, the second decade of the 21st century, I think it would be foolish to develop an RTOS-based system without using a tool like these.

Percepio has come out with an OS visualization tool they call the Tracealyzer. It has a bit of recorder code that links into the firmware. Every event recorded on a kernel-call granularity (soon to be available down to the function-call level) stuffs four bytes of data into a buffer, which is passed to the Tracealyzer application on a PC. They claim a "typical" (whatever that means) application will generated about 10 KB/sec of data, and that the recorder's overhead will eat 1 to 3% CPU overhead on most processors.

Over 22 views are offered, and the best way to describe this is by showing some of the screens.

This screen shows kernel calls over time.

Click on image to enlarge.

I like the following screen, which shows where the CPU cycles are going:

Click on image to enlarge.

You can click on one of the peaks to get more detailed data.

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