Power Profiler Kit (PPK) - modify to enable higher power measurements

Question

Hi everyone! 
 I've been using the Power Profiler Kit quite successfully for the past few months. Instead of using the UI, I designed a python app to communicate with it (through pynrfjprog and JLink RTT) and perform long-term power consumption measurements. 
 It's been working super well and reliably to perform automated QA tests on a NRF52832-based custom board. 
 I now want to perform the same kind of tests on an NRF52840-based custom board that features a cellular modem. The issue is that the peak current consumption of that board is >200mA because of the cellular modem. It's higher than the max current supported by the PPK (~70mA). 
 Would you mind sharing a way to increase that max current by reworking the PPK and modifying the current measurement shunt resistor(s)? The hardware modification is easy, but a PPK firmware modification would also most likely be needed, so that the PPK reports the right current. Is there a way to change the config of the PPK firmware through a JLink RTT command, or by writing shunt resistor values to the flash or UICR? Would you mind open-sourcing the PPK firmware so that people could customize it if needed? 
 Thanks! Lucas

wlgrd · Answer

Hi Lucas. Nice to hear that you have had good use of the PPK. 
 You can have a look at this ppk api ( set_user_resistors) to see how you can change the user-defined resistor values. These values are exposed in the initial metadata coming from the PPK as you connect, and you can use these to calculate the new values. 
 Your mileage may vary though, since the ratio between resistors are carefully selected together with the switching circuitries reference voltages, meaning that you may end up with rapid switching at times. I would advise trying to e.g triple all the values at the same time. 
 The feature of changing the initial resistor values has not been exposed since users may forever break the factory stored EEPROM values. But if you want to, you should use the same syntax as the github-link I provided, with command byte 0x10. Please be very aware that this will overwrite the factory defaults, and is not able to restore it unless you write it correctly. The user resistors may still be used though. 
 We can unfortunately not open-source the firmware at the moment.