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Project: Custom kernel for tinkerboard with overclock
Hello all.

I work on a time lab and i'm doeing some tests with tinkerboard. The procedure is: sync tinkerboard with 1 Hz signal of our atomic clock and generate 1 Hz signal with system timestamps. This output signal should be "in phase" with the input signal... Theorically. We spect that signal is not totally in phase but with a good keeping of the input signal. We already done the same procedure with raspberry pi 3b running at 1,35 GHz clock and with tinnkerboard that is running at stock clock (1,8GHz) and stock kernel (4.4.132) the results are in the freqstab_rpi_tinker picture.
For explanation: Tinkerboard has a lower phase noise and can keep the phase with more precision (~0.2 us medium) while RPi has bigger phase noise and keeps the phase with less precision (10 us medium) with more spikes.
I want to advance more: overclock the kernel to see if we have improvements at response, also implement preempt-rt patch to the updated kernel (that i will upstream from linux-stable (currently 4.4.206 for 4.4 kernels)). I trying to do this overclock but no success. I see at clk-rk3288.c file (that controls the GCC (Global Clock Controller) i think) we can reach 2,2 GHz at PLLs, but we have a frequency table that only go to 1,8 GHz. This can be also seen at .dtsi files (for tinker i think rk3288.dtsi and rk3288-miniarm.dts . I've already compilled a kernel with modifications in both files. clk-rk3288.c and dts files. But the newer frequencies doesn't apply. Is something that i'm missing out?

I will leave here the source at github that i'll post future commits with new implementations and post archieved results here. I think this is a good test to see the hardware and OS response:



You can also see some lab statistics that i've put online here:

The pps generation works on rpi and tinkerboard, just need to adapt the gpio scheme for tinker. If someone wants to try i can help it. The test on the picture was done running this program in one isolated cpu (4th core) with isolcpus=3 at extlinux.conf file and taskset -c 3 ppsout command. I've also removed the 24MHz crystal oscilator and put a signal of same frequency locked (in phase, keeping track) of an atomic clock referenced to UTC -> UTC(LRTE) and the pps input in one GPIO and output in another one.


Best regards,

Luiz Paulo

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