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May 2009
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2009-05-28 »

eieio

A few days ago someone mentioned to me a project that they'd worked on during their second co-op work term at the University of Waterloo. That reminded me of my second work term, which was just over 11 years ago (!!) now.

That job was in Montreal, at a company designing PowerPC-based videoconferencing systems. My job was to get their new (and very buggy) PowerPC motherboard booting with the embedded OS they had licensed, called pSOS.

I learned a bunch of things in order to do that job, notably how to use a logic analyzer to examine transactions on the PCI bus. Logic analyzers are tons of fun. But that's not the point of this story.

The point of this story is the PowerPC assembly language, specifically my favourite instruction of all time, eieio. It's short for "enforce in-order execution of I/O." A milder company might have named that instruction "barrier" or "sync" or something. But not Motorola.

(My first ever assembly language experience was on Motorola's 8-bit 6809 processor. They had a funny instruction there too: sex. It was short for "sign extend." Probably every processor ever made has a sign extend instruction, but nobody else was willing to call theirs "sex.")

Anyway, eieio. It's an awesome instruction because almost nobody ever needs to use it, but the people who do need it need it a lot. And those people, being low-level software developers, have a fun sense of humor. So you'd get code like this:

<i>something something</i>
<i>something something</i>
eieio

<i>something something</i>
<i>something something</i>
eieio</pre>

You could sing your source code to the tune of Old Macdonald's Farm. It was awesome.

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