This section describes, how the ED measurement for the current channel is done. The ED value is calculated by averaging the RSSI values over 8 symbols (128 us). Due to the internal processing in the radio transceiver, an ED measurement is finished after 140 us.
The 8 bit value, which is read from RG_PHY_ED_LEVEL has a valid range from ed = [0...84]
, all values from 85...255
are reserved. The power level during the measurement period is RSSI_BASE_VAL + ed
, whereas RSSI_BASE_VAL
is given in dBm
. The constant RSSI_BASE_VAL is defined in the AT86RF230 data sheet. The value ed=0
means, that the measured energy is energy<=RSSI_BASE_VAL
.
- Note:
- The ED value is erased, if the receiver detects a preamble. Therefore it is invalid within 140 us after a preamble detection.
There are two methods, how to get the ED value:
An ED measurement can be started by writing an arbitrary value to the register RG_PHY_ED_LEVEL. After 140 us the ED measurement procedure is completed and the ED value can be read from the register.
- Code example
An ED measurement is automatically started after detection of an SFD. The register RG_PHY_ED_LEVEL can be read in a time period which starts 140 us after the TRX_IRQ_RX_START interrupt (time to complete the measurement) and ends 96 us after the TRX_IRQ_TRX_END interrupt (minimum time which is needed to detect the next SFD).
- Code example
-
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