Monitoring core clock


I am now trying to observe the clock of the HiFive Unleashed core with an oscilloscope. I have read the datasheet (schematics) and the user manual, but there doesn’t seem to be any such port.

I have tried the following ports, but to no avail.

  • CHIPLINK_TX_CLK (FMC connector)
  • SPI0_SCLK (GPIO pinout)
  • TCLK (JTAG connector pinout)

In addition, I also tried the following to check the operating frequency from Linux, but it did not work.

The software I am using is Keystone Enclave v1.0.0 (OpenSBI v0.8, Linux 5.7.0, Buildroot 2020.11).

Any method that involves HW modification (soldering) or checking the clock frequency from Linux is appreciated.


If you are running freedom-u-sdk then “cpupower frequency-info” will tell you the current freq and available choices. “cpupower frequency-set” will let you set the frequency to one of the choices allowed by the dts. I don’t know when this went into the upstream linux kernel.

You can also get an estimate of frequency by using perf, e.g. “perf stat /bin/ls” tells me that the clock is 0.999GHz. This is presumably using the cycle csr and the clock to compute frequency.

I’m not a hardware guy so can’t answer the other question.

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Thank you very much, Jim.
Unfortunately, neither “cpupower” nor “perf” commands seemed to be provided in my S/W environment. I’ll check if I can change this in the Buildroot settings.