RTOS/CC2640R2F: What's going on after calling SystemReset()?

Tool/software: TI-RTOS

My development environment is like below

- IAR 7.80.3

- simplelink_cc2640r2_sdk_1_35_00_33

- Base on simpleBLEperipheral project

I want to record log message via UART so there are two wires(RX, Gnd) connecting to my cc2640r2f board.

The cc2640r2f reset every 40 seconds by calling SystemReset().

And I find the clock in cc2640r2f is increasing without being affected by the reset.

So my question is why the clock not reset after calling SystemReset()?