Will it be possible to feed in a reference clock to the ADALM-PLUTO?

Thanks for all the info in this thread, and the linked document.  I was able to successfully swap to a 26 MHz 0.5ppm TCXO (leftover from a previous project) without any issues.  Those are pretty cheap, common, and easy to find... the one I used was a 2.0mm x 1.6mm, which is smaller than the one on the board, but it fit on the pads okay.  I agree that pads for an external reference input would be nice on a future rev... though the self-contained and portable nature of the Pluto is a huge plus IMO (and 0.5ppm with 1ppb Allan variance over 1 sec is decent enough for most of my uses).

I wanted to mention two things:

1) In this doc: PlutoSDR/M2k boot magic explained [Analog Devices Wiki] , it says the variable is "ad9361_ext_refclk", though it appears to actually be "ad936x_ext_refclk".

2) Instead of modifying the device tree and rebuilding the image, I added a U-Boot environment variable for a custom frequency.  I modified the adi_loadvals line, which is what checks the ad936x_skip_ext_refclk to optionally overwrite the frequency value with the factory calibrated frequency.  I have it check for variable "ad936x_custom_refclk", and write that value if it exists.  If that doesn't exist, it loads the factory calibrated frequency.  Both of these are skipped if ad936x_skip_ext_refclk is set.

Here is the command to make that happen:

fw_setenv adi_loadvals "fdt addr $"{fit_load_address}" && fdt get value fdt_choosen /configurations/$"{fit_config}"/ fdt && fdt get addr fdtaddr /images/$"{fdt_choosen}" data && fdt addr $"{fdtaddr}"; if test ! -n $"{ad936x_skip_ext_refclk}"; then if test -n $"{ad936x_custom_refclk}"; then fdt set /clocks/clock@0 clock-frequency $"{ad936x_custom_refclk}"; elif test -n $"{ad936x_ext_refclk}"; then fdt set /clocks/clock@0 clock-frequency $"{ad936x_ext_refclk}"; fi; fi; if test -n $"{model}"; then fdt set / model $"{model}"; fi; if test -n $"{attr_name}" && test -n $"{attr_val}"; then fdt set /amba/spi@e0006000/ad9361-phy@0 $"{attr_name}" $"{attr_val}"; fi"

Then, to set the custom frequency (26 MHz in my case...  note that the quotes and < > are required):

fw_setenv ad936x_custom_refclk "<26000000>"

Just wanted to post this as it may be easier for some... and maybe AD would consider adding this functionality in their baseline, so those of us with custom frequencies could easily change frequencies using the stock firmware.

Pat

Thanks for all the info in this thread, and the linked document.  I was able to successfully swap to a 26 MHz 0.5ppm TCXO (leftover from a previous project) without any issues.  Those are pretty cheap, common, and easy to find... the one I used was a 2.0mm x 1.6mm, which is smaller than the one on the board, but it fit on the pads okay.  I agree that pads for an external reference input would be nice on a future rev... though the self-contained and portable nature of the Pluto is a huge plus IMO (and 0.5ppm with 1ppb Allan variance over 1 sec is decent enough for most of my uses).

I wanted to mention two things:

1) In this doc: PlutoSDR/M2k boot magic explained [Analog Devices Wiki] , it says the variable is "ad9361_ext_refclk", though it appears to actually be "ad936x_ext_refclk".

2) Instead of modifying the device tree and rebuilding the image, I added a U-Boot environment variable for a custom frequency.  I modified the adi_loadvals line, which is what checks the ad936x_skip_ext_refclk to optionally overwrite the frequency value with the factory calibrated frequency.  I have it check for variable "ad936x_custom_refclk", and write that value if it exists.  If that doesn't exist, it loads the factory calibrated frequency.  Both of these are skipped if ad936x_skip_ext_refclk is set.

Here is the command to make that happen:

fw_setenv adi_loadvals "fdt addr $"{fit_load_address}" && fdt get value fdt_choosen /configurations/$"{fit_config}"/ fdt && fdt get addr fdtaddr /images/$"{fdt_choosen}" data && fdt addr $"{fdtaddr}"; if test ! -n $"{ad936x_skip_ext_refclk}"; then if test -n $"{ad936x_custom_refclk}"; then fdt set /clocks/clock@0 clock-frequency $"{ad936x_custom_refclk}"; elif test -n $"{ad936x_ext_refclk}"; then fdt set /clocks/clock@0 clock-frequency $"{ad936x_ext_refclk}"; fi; fi; if test -n $"{model}"; then fdt set / model $"{model}"; fi; if test -n $"{attr_name}" && test -n $"{attr_val}"; then fdt set /amba/spi@e0006000/ad9361-phy@0 $"{attr_name}" $"{attr_val}"; fi"

Then, to set the custom frequency (26 MHz in my case...  note that the quotes and < > are required):

fw_setenv ad936x_custom_refclk "<26000000>"

Just wanted to post this as it may be easier for some... and maybe AD would consider adding this functionality in their baseline, so those of us with custom frequencies could easily change frequencies using the stock firmware.

Pat

Hi, this look to be very interesting. I'm a noob to adalm-pluto and not so expert to recompile the firmware.

I'm interested in use your solution to feed a 25mhz tcxo 0.1ppm but unfortunately while hardware mod is pretty easy to me,

I'm scratching my head trying to understand where your code must be located.

Any suggestion will be very apprecciated.

Best regards  J.

Figured out..

Hi, thank you so much for sharing this info. I have changed it to 10MHz from an external GPSDO but now I would like to change it to 25MHz, I tried the same commands above but PLUTO just got back to original 40MHz and seems no longer acceting to change to 25MHz staying locked on 40MHz, can you please detail the command sequence (including resets) to "re-change" the freq for an external reference please? Thanks.

Hello, 

thank you for an interesting solution. Did you check this code with Pluto Rev.D and SDR Console?
I tried to test Pluto rev.D with 25 MHz external reference and SDR Console application.
After loading this code Pluto is no longer detected by SDR Console. Any ideas?

Karen