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I am trying to setup two BladeRF A4 boards that share a clock. The first BladeRF uses a 10MHz input to REFIN and then is configured to output the 38.4MHz clock via CLKOUT. Everything seems to work fine with this setup.

The second board i try to setup to accept the clock from the first board via the CLKIN pin using the:
set clock_sel external

The system pauses for a few seconds before returning an error:

[ERROR @ host/libraries/libbladeRF/src/backend/usb/nios_access.c:78]
Failed to receive NIOS II response: An unexpected error occured
[ERROR @ host/libraries/libbladeRF/src/board/bladerf2/bladerf2.c:3487]
bladerf_set_clock_select: dev->backend->config_gpio_write(dev, gpio) failed:
An unexpected error

Any ideas why this is failing?

Thanks

It appears that the second slave bladeRF micro may not be receiving a clock.
Can you please run bladeRF-cli with --verbosity=verbose? Are you sure CLKOUT is enabled on the master? What kind of cable are you using? Perhaps trying a shorter, less lossy UFL might help as well.

Got exactly the same behavior.

Using to lock to an external 10MHz ref clock on the ref clock connector works fine, using to use a 38.4MHz clock on the clock in connector results in the same timeout error.

Using a Leo Bodnar GPSDO (3.3V CMOS output) without attenuator, tried with several drive currents. The ref clock input even locks if a 10dB attenuator is used (ref clock is also specified to support lower clock levels).

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