1 ===============================
2 IEEE 802.15.4 Developer's Guide
3 ===============================
4
5 Introduction
6 ============
7 The IEEE 802.15.4 working group focuses on standardization of the bottom
8 two layers: Medium Access Control (MAC) and Physical access (PHY). And there
9 are mainly two options available for upper layers:
10
11 - ZigBee - proprietary protocol from the ZigBee Alliance
12 - 6LoWPAN - IPv6 networking over low rate personal area networks
13
14 The goal of the Linux-wpan is to provide a complete implementation
15 of the IEEE 802.15.4 and 6LoWPAN protocols. IEEE 802.15.4 is a stack
16 of protocols for organizing Low-Rate Wireless Personal Area Networks.
17
18 The stack is composed of three main parts:
19
20 - IEEE 802.15.4 layer; We have chosen to use plain Berkeley socket API,
21 the generic Linux networking stack to transfer IEEE 802.15.4 data
22 messages and a special protocol over netlink for configuration/management
23 - MAC - provides access to shared channel and reliable data delivery
24 - PHY - represents device drivers
25
26 Socket API
27 ==========
28
29 ::
30
31 int sd = socket(PF_IEEE802154, SOCK_DGRAM, 0);
32
33 The address family, socket addresses etc. are defined in the
34 include/net/af_ieee802154.h header or in the special header
35 in the userspace package (see either https://linux-wpan.org/wpan-tools.html
36 or the git tree at https://github.com/linux-wpan/wpan-tools).
37
38 6LoWPAN Linux implementation
39 ============================
40
41 The IEEE 802.15.4 standard specifies an MTU of 127 bytes, yielding about 80
42 octets of actual MAC payload once security is turned on, on a wireless link
43 with a link throughput of 250 kbps or less. The 6LoWPAN adaptation format
44 [RFC4944] was specified to carry IPv6 datagrams over such constrained links,
45 taking into account limited bandwidth, memory, or energy resources that are
46 expected in applications such as wireless Sensor Networks. [RFC4944] defines
47 a Mesh Addressing header to support sub-IP forwarding, a Fragmentation header
48 to support the IPv6 minimum MTU requirement [RFC2460], and stateless header
49 compression for IPv6 datagrams (LOWPAN_HC1 and LOWPAN_HC2) to reduce the
50 relatively large IPv6 and UDP headers down to (in the best case) several bytes.
51
52 In September 2011 the standard update was published - [RFC6282].
53 It deprecates HC1 and HC2 compression and defines IPHC encoding format which is
54 used in this Linux implementation.
55
56 All the code related to 6lowpan you may find in files: net/6lowpan/*
57 and net/ieee802154/6lowpan/*
58
59 To setup a 6LoWPAN interface you need:
60 1. Add IEEE802.15.4 interface and set channel and PAN ID;
61 2. Add 6lowpan interface by command like:
62 # ip link add link wpan0 name lowpan0 type lowpan
63 3. Bring up 'lowpan0' interface
64
65 Drivers
66 =======
67
68 Like with WiFi, there are several types of devices implementing IEEE 802.15.4.
69 1) 'HardMAC'. The MAC layer is implemented in the device itself, the device
70 exports a management (e.g. MLME) and data API.
71 2) 'SoftMAC' or just radio. These types of devices are just radio transceivers
72 possibly with some kinds of acceleration like automatic CRC computation and
73 comparison, automagic ACK handling, address matching, etc.
74
75 Those types of devices require different approach to be hooked into Linux kernel.
76
77 HardMAC
78 -------
79
80 See the header include/net/ieee802154_netdev.h. You have to implement Linux
81 net_device, with .type = ARPHRD_IEEE802154. Data is exchanged with socket family
82 code via plain sk_buffs. On skb reception skb->cb must contain additional
83 info as described in the struct ieee802154_mac_cb. During packet transmission
84 the skb->cb is used to provide additional data to device's header_ops->create
85 function. Be aware that this data can be overridden later (when socket code
86 submits skb to qdisc), so if you need something from that cb later, you should
87 store info in the skb->data on your own.
88
89 To hook the MLME interface you have to populate the ml_priv field of your
90 net_device with a pointer to struct ieee802154_mlme_ops instance. The fields
91 assoc_req, assoc_resp, disassoc_req, start_req, and scan_req are optional.
92 All other fields are required.
93
94 SoftMAC
95 -------
96
97 The MAC is the middle layer in the IEEE 802.15.4 Linux stack. This moment it
98 provides interface for drivers registration and management of slave interfaces.
99
100 NOTE: Currently the only monitor device type is supported - it's IEEE 802.15.4
101 stack interface for network sniffers (e.g. WireShark).
102
103 This layer is going to be extended soon.
104
105 See header include/net/mac802154.h and several drivers in
106 drivers/net/ieee802154/.
107
108 Fake drivers
109 ------------
110
111 In addition there is a driver available which simulates a real device with
112 SoftMAC (fakelb - IEEE 802.15.4 loopback driver) interface. This option
113 provides a possibility to test and debug the stack without usage of real hardware.
114
115 Device drivers API
116 ==================
117
118 The include/net/mac802154.h defines following functions:
119
120 .. c:function:: struct ieee802154_dev *ieee802154_alloc_device (size_t priv_size, struct ieee802154_ops *ops)
121
122 Allocation of IEEE 802.15.4 compatible device.
123
124 .. c:function:: void ieee802154_free_device(struct ieee802154_dev *dev)
125
126 Freeing allocated device.
127
128 .. c:function:: int ieee802154_register_device(struct ieee802154_dev *dev)
129
130 Register PHY in the system.
131
132 .. c:function:: void ieee802154_unregister_device(struct ieee802154_dev *dev)
133
134 Freeing registered PHY.
135
136 .. c:function:: void ieee802154_rx_irqsafe(struct ieee802154_hw *hw, struct sk_buff *skb, u8 lqi)
137
138 Telling 802.15.4 module there is a new received frame in the skb with
139 the RF Link Quality Indicator (LQI) from the hardware device.
140
141 .. c:function:: void ieee802154_xmit_complete(struct ieee802154_hw *hw, struct sk_buff *skb, bool ifs_handling)
142
143 Telling 802.15.4 module the frame in the skb is or going to be
144 transmitted through the hardware device
145
146 The device driver must implement the following callbacks in the IEEE 802.15.4
147 operations structure at least::
148
149 struct ieee802154_ops {
150 ...
151 int (*start)(struct ieee802154_hw *hw);
152 void (*stop)(struct ieee802154_hw *hw);
153 ...
154 int (*xmit_async)(struct ieee802154_hw *hw, struct sk_buff *skb);
155 int (*ed)(struct ieee802154_hw *hw, u8 *level);
156 int (*set_channel)(struct ieee802154_hw *hw, u8 page, u8 channel);
157 ...
158 };
159
160 .. c:function:: int start(struct ieee802154_hw *hw)
161
162 Handler that 802.15.4 module calls for the hardware device initialization.
163
164 .. c:function:: void stop(struct ieee802154_hw *hw)
165
166 Handler that 802.15.4 module calls for the hardware device cleanup.
167
168 .. c:function:: int xmit_async(struct ieee802154_hw *hw, struct sk_buff *skb)
169
170 Handler that 802.15.4 module calls for each frame in the skb going to be
171 transmitted through the hardware device.
172
173 .. c:function:: int ed(struct ieee802154_hw *hw, u8 *level)
174
175 Handler that 802.15.4 module calls for Energy Detection from the hardware
176 device.
177
178 .. c:function:: int set_channel(struct ieee802154_hw *hw, u8 page, u8 channel)
179
180 Set radio for listening on specific channel of the hardware device.
181
182 Moreover IEEE 802.15.4 device operations structure should be filled.
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