Hmmm, Not that I’m aware of maybe someone else can comment, I would think the QSPI flash is where you can store the data before a sleep and system reset as the only wakeup method? I use only Mbed afaik it’s the only way to get BLE and IMU together and patch or hack Battery reading and Sleep mode lameness.
I’m looking toward getting RTC low power INT generated and save data in Flash for my next push. The BLE IMU data notify and connectivity to the MIT AI2 is very good and reliable for me. It’s battery reading and sleep ALL or nothing that SUCK. Nordic has it figured out and so does adafruit, SEEED ?
HTH
GL 
PJ