AM3358 on 300 MHz

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1

I’m confused how the BBB can run on 300 MHz.

The BeagleBone has a AM3358 processor, and according to http://www.ti.com/lit/ds/symlink/am3358.pdf, it supports 600, 800, and 1000 Mhz, not 300 MHz. Still, using tools like cpufreq-set, you can set the frequency to 300. The power usage drops indeed and the CPU power is lowered pro rato.

Does someone what happens? Is 300 a frequency which is unsupported by TI’s AM3358? If so, are there any risks?

Thanks, Mark

2

I do not know the technical reasons how, but I do know that 300Mhz has been the low end of cpufreq-set for a good long time now. Which is what the ondemand governor uses when CPU load is less than ~66%. Otherwise the processor can go up to 1Ghz when CPU load is greater than ~66%.

Anyway, I’ve been using ondemand mostly for well over a year I believe. No ill effects on my circuitco A5A, or element 14 REV C’s( we have 2 A5A’s and 3 REV C’s ).

3

According to http://www.ti.com/lit/ds/sprs717h/sprs717h.pdf, the AM3358 supports three frequencies: 1000, 800, and 600 MHz (table 3-1).
The BeagleBone Black is equipped with the SoC am3358bzcz100. According to paragraph 5.4, the so called Operating Performance Points for this SoC are (table 5-7):

VDD_MPU OPP ARM (A8)

Nitro 1000 MHz
Turbo 800 MHz
OPP100 600 MHz
OPP50 300 MHz

Some peripherals and features have limited support when the device is operating in OPP50 (paragraph 7.3), like unsupported DDR3 (much to my believe the BBB uses) and reduced DDR2 performance.

Then 300 MHz runs the BeagleBone in a limited way? This is not what we’ve seen here. So I’m still confused why the AM3358 does not support 300 MHz (and BTW the AM3352 does, 300, 600, and 1000).

Mark

4

I think you’re worrying too much about the little things. If you do not want to use 300Mhz frequency, then use a CPU governor that uses something else.