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Oct 10, 2015, 12:22 AM
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Odroid test 1

With all its dependancies resolved, the odroid finally underwent its most challenging task ever documented. The vision program compiled & processed the 160x120 test footage at slightly over 30fps. It was way below the predicted 72fps from nbench results. Fortunately, at 160x120, it had no problem consuming the webcam's maximum framerate. The latency would be 1/4 of whatever the framerate was, since it used a pipeline to parallelize an algorithm that was otherwise not parallelizable.

It sucked 2.2A at 7.4V with the fan wirring at full speed & webcam on. The Turnigy converter got scorching, even converting this meager voltage down to 5V.

At 320x240, it was hopelessly slow again at 4fps from the webcam. The CPUs maxed out & used 2.2A at 7.4V. Idle current was 0.65A at 7.4V or 1A at 5V. There was no sign of any frequency scaling. The A7's were always at 1.4Ghz & the A15's were always 2Ghz.

As predicted, it only used 4 CPUs at a time, no matter how many the vision program was configured to use. The kernel automatically allocated the 4 Cortex-A15's to the vision program, only occasionally using the Cortex-A7's. It was unknown whether 4 CPUs was the maximum of both A7's & A15's in use simultaneously, or whether it had to stop the A15's to use any A7.

CFLAGS were hard to come by, but the following seemed to work well:

-O3 -pipe -mcpu=cortex-a15 -mfloat-abi=hard -mfpu=neon-vfpv4

It was still an astounding step up, compared to what the PI or the Gumstixs brought. It was of course the power of billions of premium contracts subsidizing phones that led to such huge gains in the Odroid's Samsung processor. The set top box market that led to the PI's Broadcom processor wasn't nearly lucrative enough to generate such powerful chips. Set top boxes were a race to the bottom while phones were a race to the top. Because cell phones are a vital business expense, they benefited from tax writeoffs & corporate budgets while set top boxes were squarely funded by what meager budgets consumers had after taxes.
Last edited by Jack Crossfire; Oct 10, 2015 at 02:26 PM.
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