decaWave DW1000, User Manual

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DW1000 User Manual
© Decawave Ltd 2017 Version 2.12 Page 220 of 242
11 APPENDIX 2: The IEEE 802.15.4 MAC layer
This appendix gives an introduction to some aspects of the MAC layer defined in the IEEE 802.15.4 – 2011
standard. The DW1000 transceiver does not implement the MAC layer. The MAC layer implementation is
the responsibility of the host microprocessor system controlling the DW1000. However the DW1000
includes some features to help with the MAC layer implementation. These are:

CRC generation and checking, (see section 5.1 – Cyclic redundancy check ).

Frame filtering, (see section 5.2 – Frame filtering ).

Automatic acknowledgement, (see section 5.3 – Automatic Acknowledgement ).

Automatic turn-around to receive acknowledgement and other responses, (see section 5.4 –
Transmit and automatically wait for response )
An introduction to the MAC frame format is given by the sub-sections below. For more details the reader is
referred to the standard itself [1].
11.1 General MAC message format
The MAC message occupies the Data portion of the UWB Frame as described in section 10.1 – Frame
structure overview and shown in Figure 31. This may be up to 127 octets in length according to the standard,
and up to 1023 octets when employing the DW1000’s non-standard long frame mode, see section 3.4 –
Extended Length Data Frames . The general structure of a MAC message consists of a header that identifies
the frame, followed by a variable length (possibly zero) payload typically from the upper layers but
sometimes (as in the case of MAC command frames) generated within the MAC itself, and finally ended by
the MAC footer which is the FCS (Frame Checking Sequence) CRC used to detect transmission errors. Figure
34 shows the components of the MAC message frame in more detail, indicating the number of octets in each
component.
Figure 34: General MAC message format
The MAC header is parsed by the DW1000 as part of the frame filtering function to determine if its
destination address matches the IC’s address information programmed in
Register file: 0x01 – Extended
Unique Identifier and Register file: 0x03 – PAN Identifier and Short Address (or if the frame is a broadcast
message). This parsing of receive frame is based on the contents of the Frame Control field (at the start of
the MAC header) described in section 11.2 below.
Frame
Control
2
octets
MAC Header (MHR) MAC Payload
MAC Footer
(MFR)
Sequence
Number
1
octet
Destination
PAN Identifier
Destination
Address
Source PAN
Identifier
Source
Address
Aux Security
Header
Frame Payload FCS
0 or 2
octets
0, 2 or 8
octets
0 or 2
octets
0, 2 or 8
octets
0, 5, 6 10 or 14
octets
Variable number of
octets
2
octets