I’m using the BeagleBone as the CPU in a voltage monitoring device.
I created a cape with some SPI A2D devices on it and use the 7 ADC channels in the BeagleBone to increase the number of monitored voltages.
I’m using an Ubuntu user space with a custom kernel to enable three SPI chip selects and both SPI controllers. This is all working fine and has been for some time.
I wasn’t initially using the 7 additional ADC channels, but now I need those additional inputs.
My lab system works fine when I read the ADC channels (the readings are bit wild and I have to do significant filtering on the returned values, but that’s another post…)
But when I tried to build a second system that used the ADC channels, it fails. The TSC (touch screen controller) driver fails to load on two different BeagleBone boards I tried using with the following error:
tsc tsc: clock input less than min clock requirement
tsc: probe of tsc failed with error -22
And when I check earlier in the kernel output, I find this:
OMAP clockevent source: GPTIMER2 at 19200000 Hz
But on the system that works, I see this:
OMAP clockevent source: GPTIMER2 at 24000000 Hz
There were two other diffs in the dmesg:
The RTC wasn’t set so it set the time to year 2000. I tried setting the RTC but this doesn’t seem to have resolved the problem.
And the slower clock led to a lower BogoMIPS…
Calibrating delay loop… 548.86 BogoMIPS (lpj=2744320)
Calibrating delay loop… 437.45 BogoMIPS (lpj=2187264
In both cases, my system is running off 5V power provided through the cape and not from USB power, so this shouldn’t be the power limiting due to USB power limits. I verified that the provided power is 4.9 volts or higher.
I can’t find any u-boot or kernel setting to control this and it doesn’t seem like it’s the USB powered speed limiting documented in the manual.
Does anyone have any idea why two boards boot at 19.2MHz and one system boots at 24MHz?
Any ideas where that configuration setting is coming from? I tried moving the microSD card from the working (24MHz) system to the failing (19.2MHz) system and the “slow” system still boots slow, so it doesn’t seem to be anything in the microSD image (u-boot, kernel, OS config, etc.)