CC2520 auto ack mode

Hi,
are you sure AUTOCRC field in FRMCTRL0 register is not set to '0' when the ACK is received?
The ACK frame should be received by the node and FCS is correct, and the receiver node has auto-crc setting, then the most significant bit of the first byte of the FCS frame returns the result of the FCS computation as done by the HW.
However, if AUTOCRC is set to 0, then the two FCS bytes contain the actual FCS field OTA and the CRC computation must be done in SW.

Thanks,
TheDarkSide

Hi TheDarkSide, thank you for your prompt answer.
With AUTOCRC = 1 you wrote the FCS computation result is the MSBit of the first byte of the FCS field, but in the datasheet is the MSBit in the second one (section 20.3.4) is it an error in the ds?

I'm using your basicRf source code ported on my microcontroller (not TI), so the AUTOCRC is set only once during the init routine. Also I see the two FCS bytes changing even keeping the seq number unchanged (this should produce always the same value of the FCS if AUTOCRC=0)

regards
Stefano

Hi again,
I did some more investigations...AUTOCRC is always set to 1.
Receiving a "standard" frame (not automatically sent by the chip) the two FCS (rssi+crc_ok bit+correlation) bytes are ok, but receiving the automatically generated ack, these two bytes are swapped in the rxfifo
very strange!

Stefano

Hi Stefano,
my mistake on the byte which carries the CRC_OK bit. It is the second one.
I checked in the TI-MAC code and the way we check the CRC is the same whether that was a plain 802.15.4 data frame or a MAC ACK frame. It is very unlikely that there was an issue like that, because that would mean we wouldn't be able to recognize any acknowledgment.

One thing I want to make sure is whether you are retrieving the right data for the MAC ACK.
MACK ACK is a special frame, only 5 bytes + 1 byte of PHY header (which carries the length of the PHY payload, ie 5 bytes).
So your array should contain 6 bytes in the fifo, and byte 5 and 6 should be respectively RSSI and CRC_OK+correlation.

Please check out for your reference the code in Components\mac\low_level\srf04\mac_rx.c

Thanks,
TheDarkSide