802.15.4 CCA mode 2 (Carrier Sense) implementation on CC2520

I think you just need to read the IEEE 802.15.4 standard. Honestly most chipsets provide this in low level source or even in HW level

Rui

Let me elaborate a bit.

CC2520 offers 4 CCA modes by setting CCACTRL1 bit 4:3 to the following:

00 : CCA always set to ‘1’
01 : CCA = ‘1’ when RSSI < CCA_THR-CCA_HYST, CCA = ‘0’ when RSSI >= CCA_THR
10 : CCA = ‘1’ when not receiving a frame, else CCA = ‘0’
11 : CCA = ‘1’ when RSSI < CCA_THR-CCA_HYSTand not receiving a frame, CCA=0 when RSSI >= CCA_THR or receiving a frame 

Compared to 802.15.4 CCA modes:

CCA Mode 1: Energy above threshold. CCA shall report a busy medium upon detecting any energy above the ED threshold.

CCA Mode 2: Carrier sense only. CCA shall report a busy medium only upon the detection of a DSSS signal. This signal may be above or below the ED threshold.

CCA Mode 3: Carrier sense with energy above threshold. CCA shall report a busy medium upon the detection of a DSSS signal with energy above the ED threshold.

It seems to be CC2520 does not offer an option to use Carrier sense for CCA?

Or I see, sorry for  my misunderstanding, I don't quite understanding your claim"CC2520 does not offer an option to use Carrier sense for CCA", CCA modes are provided, why it dose not offer CCA?

in your case, CC2520 CCACTRL1 bit 4:3 [01] = CCA mode 1 in 802.15.4, CC2520 CCACTRL1 bit 4:3[10] = CCA mode 2 in 802.15.4, CC2520 CCACTRL1 bit 4:3 [11] = CCA mode 3 in 802.15.4

Rui