SIGNALS

Has this ever happened to you? You’re cruising down the boulevard, listening to your favorite music on your favorite radio station, then suddenly your infotainment system goes dead. WTH? If you were driving a Mazda, this might sound all too familiar.

Car radios still contain the traditional bits and pieces of analog radio circuitry, but they also contain IBOC (in-band on-channel) digital radio hardware and software. In particular, newer radios receive AM and FM analog radio transmissions and they also receive HD radio data streams in the same bands. That data provides higher audio fidelity and the ability to add auxiliary data such as images. But as with all things digital, if there’s a 0 or 1 in the wrong place, bad things can happen.

And last year, bad things did indeed happen. Drivers in the wrong place (Seattle) at the wrong time (January 30, 2022), driving the wrong kind of car (Mazda), with the wrong radio (manufactured sometime between 2014 and 2017), listening to the wrong radio station (KUOW 94.9), receiving the wrong signal (IBOC), were doubtlessly surprised when suddenly their radios went haywire. The good news: the radio would receive 94.9. The bad news: it was stuck there and the rest of the infotainment system — clock, Bluetooth, navigation, back-up camera, etc. — gone.

If you guessed that something in the broadcast data stream wasn’t kosher, you are correct. Subsequent analysis showed that the station had transmitted an image file with a name that lacked an extension (like .jpg, .png, etc.). Mazda radios tuned to that station at that time obediently received the file but, crucially and inexplicably, the radio’s firmware was unable to recognize file names lacking an extension. When it received the whiffed file name, the radio was thoroughly confused; it crashed and rebooted — a “boot loop” that would last for all eternity or until the car was crushed, whichever came first. Even worse, there was no way to restore the radio’s functionality. Apparently there wasn’t even a CTRL+ALT+DEL break-glass-incase-of-fire remedy. Oh — maybe disconnecting the battery for a few minutes? Nope.

You could blame the radio station for broadcasting disallowed files. But the real fault lies with the manufacturer of the encoding equipment the station was using. In particular, the equipment was from Xperi, a well-regarded corporation in the HD Radio sandbox (and owner of DTS and TiVO). Some software (like Windows) forces you to add a file extension but other software (like GNU/Linux) does not. In this case, apparently the whole file extension thing slipped through the cracks.

Or, you could blame Mazda (or whichever vendor wrote the infotainment code for them) for not checking the input data for validity, or at least providing a recovery method. Frankly, any device that is essentially destroyed because of an unexpected data input shows a serious lack of competency. Data streams arriving from Lord knows where absolutely must be checked and double-checked for validity, not to mention malware. The bad news: the only remedy was a new ‘Connectivity Master Unit’ that cost $1,500. The good news: Mazda agreed to cover the cost, subject to supply-chain availability.

Radio Ga Ga
For the rest of us, this is a cautionary tale. The problem is that such events occur far too often. Consider these additional anecdotes of radio broadcasts messing with radios from various car makers: In one case, car batteries kept going dead; the problem was traced to the radios; even when the radios were apparently turned off, a mischievous broadcast signal had caused the radios to continue to draw power, thus killing the batteries. The remedy? New radios.

In another case, some radios were temporarily corrupted by an errant signal from an encoder that had been updated. The remedy? Patiently wait for another update to fix the previous update. In still another case, the radios in some vehicles crashed when tuned to a podcast called “99% Invisible;” the operating system was unable to correctly read the “%” in the title. The remedy? The podcast authors created a special feed for those car owners in which the “%” was spelled as “percent.” I kid you not.

Of course, this kind of unruly behavior is not limited to car radios. It can happen to any kind of software-driven device. The simple fact is that we have no way of vetting the code inside the software devices we rely on every day. We are at the mercy of caffeine-junkie (no offense intended, just stating the facts) programmers who write those hundreds of millions of lines of code. When the stars align (or crash into each other) we get one of those “Wow! That’s weird!” software events — sometimes followed by a hardware brick event.

A final note: Soon self-driving cars will be everywhere. And I’m sure AI will control all the traffic lights. Good luck to us all. We’ll need it.

Ken C. Pohlmann is an electrical engineer specializing in audio topics as a consultant and writer. He is Professor Emeritus at the University of Miami.