Hi there. I am using an NRF52832 target and have configuration code in my target image which sets up the SWO port to run at 4 MHz (CPU @ 64 MHz). I would like to use my Segger J-Link Base and the jLinkSWOViewerCL command-line application (JLink_V632a) to view the SWO output from the board: I do not want jLinkSWOViewerCL to configure my target hardware at all, I just want it to view the SWO output from the target HW as I have already configured it.

I have tried various combinations of command line options but I cannot make jLinkSWOViewerCL simply read the output: it always wants to configure the target and figure out an SWO frequency for itself and I can't make it stop doing that.

Is there a way?

In case it is of interest, this is the target code that configures the SWO output (it is an mbed-os environment):

FYI, this is the closest I have got. With the command-line below my prints of "Hello World.\n" every second come out as "H" (i.e. the initial letter) followed by nothing else every second, so I don't think jLinkSWOViewerCL has listened to my -cpufreq (and it also says 0 kHz in the command output).

jLinkSWOViewerCL -cpufreq 64000000 -swofreq 4000000 -device NRF52832_XXAA

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* SEGGER Microcontroller GmbH *
* Solutions for real time microcontroller applications *
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* (c) 2012 - 2017 SEGGER Microcontroller GmbH *
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* SEGGER J-Link SWO Viewer Compiled Apr 30 2018 15:46:03 *
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------------------------------------------------------------
Usage:
In the configuration dialog enter the target CPU frequency
or the target device name.
SWO Viewer can show data from stimulus ports 1 to 16.
0 - 9 and a - f keys toggle display of stimulus port data.
Ctrl-C and any other key closes SWO Viewer
------------------------------------------------------------


Target CPU (NRF52832_XXAA) is running @ 64712 kHz.
Receiving SWO data @ 0 kHz.
Showing data from stimulus port(s): 0
-----------------------------------------------
HHHH
HHrHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH

Unfortunately I'm using software which always configures the ITM; Nordic's NRF52832 target in mbed-os does this at boot. I will try hacking it out and see if that helps but it's not ideal as I then can't use the master mbed-os code directly: surely I should be able to tell J-Link what I've configured as the SWO clock frequency and it will just do it? That's certainly what the -swofreq command-line option looks as though it should be for.

I've now removed the TRACECONFIG, PIN_CNF (for pin 18) and TPI->ACPR lines, so the entire ITM init, from the code but the result remains the same as above (just the initial letter of my printf() appears); I suppose this is to be expected as starting jLinkSWOViewerCL with the command-line:

jLinkSWOViewerCL -device NRF52832_XXAA

...will likely overwrite the boot settings anyway.

Interestingly, if I leave the ITM initialisation in my code and then use GDB to download the code and view the SWO output (through my JLink Base) then it is able to view the SWO output, though it adds three white-spaces after each character:

H e l l o w o r l d .

[Can't make this forum leave my formatting alone: there are THREE white-spaces between each character above, not one]

I expect this is because the ITM register outputs 4-byte words and, of course, I'm only writing characters. Could it be that jLinkSWOViewerCL is seeing the other three NULL bytes and interpreting them as an end of string?

Sorry, posted at the same time. Many thanks for checking this. I am using V632a and the target is a commercial u-blox NINA-B1 module on its evaluation board. I think there's something in the above: how does jLinkSWOViewerCL interpret the four bytes coming out of the SWO output?

Yes, that's definitely it, you're off the hook: writing four characters into the 4 bytes of the ITM register at a time does the trick. I've raised this with mbed-os to get their implementation changed to be friendly to this sort of client. Many thanks!