CC2755R10: No need for 32.768KHz crystal.

Hi Jens,

There is the understanding of clock accuracy between using the LF RCOSC and and LF XTAL, as demonstrated in the Clock configuration section of the BLE5-Stack User's Guide, but so long as this is an acceptable tradeoff for your application then the external 32 kHz crystal can be excluded.

Regards,
Ryan

We are not using sleepmode so the answer is yes?

That certainly helps the case for RCOSC, TI does not validate all radio operations without the external 32 kHz crystal and the LF clock source still supplies the RTC and Watchdog in any power mode so developers are advised to pay close attention to timings/accuracy during testing/certification of their product within this use case.

Regards,
Ryan

Here are some more details on the register involved: https://dev.ti.com/tirex/explore/content/simplelink_lowpower_f3_sdk_8_40_00_61/docs/driverlib/cc27xx/register_descriptions/CPU_MMAP/CKMD.html#LFCLKSEL 

Since LF clock and standby should be disabled, the F3 SDK examples need to be modified to select PowerCC23X0_doWFI as the Policy Function (SysConfig -> Power module) and not use the PowerLPF3_selectLFOSC or PowerLPF3_selectLFXT APIs in Board_init (inside ti_drivers_config.c generated by SysConfig).

Regards,
Ryan

It's ok to change power policy in syscfg tool but manually change ti_drivers_config.c to exclude PowerLPF3_selectLFOSC or PowerLPF3_selectLFXT is not great since ti_drives_config.c updates on every build

Hey Brian,

You will have to exclude the ti_drivers_config.c from building in the Sysconfig Generated Files view and copy a previous ti_drivers_config.c built file into your local workspace (which you can modify accordingly) to use instead.

Regards,
Ryan