NRF52820-QDAA-R datasheet(179/437 Pages) NORDIC

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Peripherals

IEEE 802.15.4 ED measurement example

#define ED_RSSISCALE 4 // From electrical specifications

uint8_t sample_ed(void)

{

int val;

NRF_RADIO->TASKS_EDSTART = 1; // Start

while (NRF_RADIO->EVENTS_EDEND != 1) {

// CPU can sleep here or do something else

// Use of interrupts are encouraged

}

val = NRF_RADIO->EDSAMPLE * ED_RSSISCALE; // Read level

return (uint8_t)(val>255 ? 255 : val);

// Convert to IEEE 802.15.4

scale

}

For scaling between hardware value and dBm, see equation Conversion between hardware value and dBm

on page 181.

The mlme-scan.req primitive of the MAC layer uses the ED measurement to detect channels where there

might be wireless activity. To assist this primitive, a tailored mode of operation is available where the

ED measurement runs for a defined number of iterations keeping track of the maximum ED level. This is

enganged by writing the EDCNT register to a value different from 0, where it will run the specified number

of iterations and report the maximum energy measurement in the EDSAMPLE register. The scan is started

with EDSTART task and its end indicated with the EDEND event. This significantly reduces the interrupt

frequency and therefore power consumption. The following figure shows how the ED measurement will

operate depending on the EDCNT register.

128 µs

EDCNT = 0

EDSTART

EDEND

Scan 0

EDCNT = N-1

EDSTART

EDEND

Scan 1

Scan N-1

...

128*(N) µs

Figure 69: Energy detection measurement examples

The scan is stopped by writing the EDSTOP task. It will be followed by the EDSTOPPED event when the

module has terminated.

6.12.13.4 Clear channel assessment (CCA)

4463_156 v1.0

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