B MCU Real-Time Tracing

How to Trace MCU Code in (Almost) Real Time

- By Stuart Ball

How do you trace code execution in an MCU? This month, Stuart looks at the problem and offers real-time solutions.

Many years ago, I went to work for a company that had recently been acquired. They had a new product in development and the acquisition had delayed things. They were scrambling to meet deadlines. This was back when the 8088/8086 were state-of-the-art microprocessors and emulators were the size of a shoebox. I had only been there a few weeks, and the software team had been trying to solve an intermittent issue for some time, not sure if it was a hardware or software problem.

One Saturday, three software engineers and myself were "volunteered" to come in early to work on this. We didn’t make much progress, but we were using a logic analyzer that just wasn’t up to the job. By the end of the day, the project manager came down to the lab and asked what was needed. I said "Get me an HP1630 logic analyzer and I can solve this." Kind of a brash statement, I know, but I had used the HP1630 at a previous job and knew its capabilities.

The manager went back to his office and rented an HP1630 for expedited delivery the next week. The analyzer arrived on Tuesday morning and by Tuesday afternoon, I had identified the problem—it was a subtle logic error in the hardware design on one of the boards. My next assignment was to get quotes and put in a purchase requisition for two HP1631 logic analyzers. Once they arrived, nobody wanted to use the old one. I don’t even remember what brand it was.