RSSI period

Hi,

I want to use the RSSI feature for CCA, i.e. measure background signal strength. The radio is started in RX mode, then I use the following code to get one RSSI sample:

NRF_RADIO->EVENTS_RSSIEND = 0;
NRF_RADIO->TASKS_RSSISTART = 1U;
while (NRF_RADIO->EVENTS_RSSIEND == 0)
{
    // wait
}
rssi = NRF_RADIO->RSSISAMPLE;

According to the documentation I would assume that the while loop waits for about 8 usecs (typical RSSI_PERIOD), but when measuring it (using timer), it takes less than 1 usecs only. Is this expected behaviour? The value looks reasonable, but can I trust it?

-Cornelius