Texas Instruments SimpleLink CC2620 Technical Reference Manual page 1532

IEEE 802.15.4
23.5.4.1 RX Operation
The receive radio operation is a background-level operation, started with the CMD_IEEE_RX command
and using the command structure given in
At the start of an RX operation, the radio CPU waits for the start trigger, then programs the frequency
based on the channel parameter. If channel is 0xFF, the operation keeps running on an already
configured channel. This requires that the operation follows another receive operation or a synthesizer
programming operation. If the frequency synthesizer is not running, the operation ends with an error. After
programming the frequency, the radio CPU configures the receiver to receive IEEE 802.15.4 packets.
When the demodulator obtains sync on a frame, the PHY header is read first. The 7 LSBs of this byte give
the frame length. The further treatment depends on the setting of frameFiltOpt. If frameFiltOpt.frameFiltEn
is 1, further frame filtering is done as explained below. If it is 0, no frame filtering is done.
The number of bytes given by the received PHY header are received and stored in the receive queue
given by pRxQ. The format depends on rxConfig, and is as explained in
bytes of the PHY payload are the FCS, or CRC, for the packet. These bytes are checked according to the
FCS specification, and the further treatment depends on the CRC result.
If there is a CRC error and rxConfig.bAutoFlushCrc is 1, the packet is discarded from the RX buffer. If
there is no available RX buffer with enough available space to hold the received packet, the received data
is discarded. If frameFiltOpt.frameFiltStop is 1, the reception stops, otherwise the packet is received so
that the CRC can be checked.
23.5.4.1.1 Frame Filtering and Source Matching
If frameFiltOpt.frameFiltEn is 1, frame filtering and source matching are performed as described in this
section. The frame filtering may have several purposes:
• Distinction between different packet types
• Rejection of packets with a nonmatching destination address
• Rejection of packets with unknown version or illegal fields
• Automatic identification of source address
• Automatic acknowledgment transmission
• Automatic insertion of pending data bit based on source address
23.5.4.1.1.1 Frame Filtering
When frame filtering is enabled, the MAC header of the packet is investigated by the radio CPU. The
frame control field (FCF) is checked first. The frame type subfield is the first subfield of the FCF to be
checked, and determines the further processing. The MSB of the frame type is processed according to
frameFiltOpt.modifyFtFilter before the check is made. The result of this modification is only used when
checking, not when storing the FCF in the RX queue entry. For each of the eight possible values of the
frame type field (included 4 reserved ones), the frame can be setup to be accepted or rejected. This is
controlled by the bits of frameTypes. If the frame type is Acknowledgment (010b) and a CMD_RX_ACK
operation is running in the foreground, the packet is processed further, even if frameTypes.bAcceptFt2Ack
is 0. More details on the processing in that case are given in
Filtering is performed on the Frame Version and Reserved subfields. If the frame version is greater than
frameFiltOpt.maxFrameVersion, the frame is rejected.
If the Reserved subfield AND-ed with frameFiltOpt.fcfReservedMask is nonzero, the frame is rejected. The
addressing fields are checked to see if the frame must be accepted or not. This filtering follows the rules
for third-level filtering (refer to the IEEE 802.15.4 standard). When checking against the local address, the
localExtAddr or localShortAddr field is used, and when checking against the local PAN ID, the localPanID
field is used.
If frameFiltOpt.bStrictLenFilter is 1 and the frame type indicates that the frame is an acknowledgment
frame, the frame is rejected if the length of the PHY payload is not 5, which is the length of a correctly-
formulated ACK frame.
1532
Radio
Table 23-59.
Copyright © 2015, Texas Instruments Incorporated
Section 23.6.3.1. The last two
Section 23.5.4.5.
SWCU117C – February 2015 – Revised September 2015
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