1===============================
2IEEE 802.15.4 Developer's Guide
3===============================
4
5Introduction
6============
7The IEEE 802.15.4 working group focuses on standardization of the bottom
8two layers: Medium Access Control (MAC) and Physical access (PHY). And there
9are 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
14The goal of the Linux-wpan is to provide a complete implementation
15of the IEEE 802.15.4 and 6LoWPAN protocols. IEEE 802.15.4 is a stack
16of protocols for organizing Low-Rate Wireless Personal Area Networks.
17
18The 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
26Socket API
27==========
28
29.. c:function:: int sd = socket(PF_IEEE802154, SOCK_DGRAM, 0);
30
31The address family, socket addresses etc. are defined in the
32include/net/af_ieee802154.h header or in the special header
33in the userspace package (see either http://wpan.cakelab.org/ or the
34git tree at https://github.com/linux-wpan/wpan-tools).
35
366LoWPAN Linux implementation
37============================
38
39The IEEE 802.15.4 standard specifies an MTU of 127 bytes, yielding about 80
40octets of actual MAC payload once security is turned on, on a wireless link
41with a link throughput of 250 kbps or less.  The 6LoWPAN adaptation format
42[RFC4944] was specified to carry IPv6 datagrams over such constrained links,
43taking into account limited bandwidth, memory, or energy resources that are
44expected in applications such as wireless Sensor Networks.  [RFC4944] defines
45a Mesh Addressing header to support sub-IP forwarding, a Fragmentation header
46to support the IPv6 minimum MTU requirement [RFC2460], and stateless header
47compression for IPv6 datagrams (LOWPAN_HC1 and LOWPAN_HC2) to reduce the
48relatively large IPv6 and UDP headers down to (in the best case) several bytes.
49
50In September 2011 the standard update was published - [RFC6282].
51It deprecates HC1 and HC2 compression and defines IPHC encoding format which is
52used in this Linux implementation.
53
54All the code related to 6lowpan you may find in files: net/6lowpan/*
55and net/ieee802154/6lowpan/*
56
57To setup a 6LoWPAN interface you need:
581. Add IEEE802.15.4 interface and set channel and PAN ID;
592. Add 6lowpan interface by command like:
60# ip link add link wpan0 name lowpan0 type lowpan
613. Bring up 'lowpan0' interface
62
63Drivers
64=======
65
66Like with WiFi, there are several types of devices implementing IEEE 802.15.4.
671) 'HardMAC'. The MAC layer is implemented in the device itself, the device
68exports a management (e.g. MLME) and data API.
692) 'SoftMAC' or just radio. These types of devices are just radio transceivers
70possibly with some kinds of acceleration like automatic CRC computation and
71comparation, automagic ACK handling, address matching, etc.
72
73Those types of devices require different approach to be hooked into Linux kernel.
74
75HardMAC
76-------
77
78See the header include/net/ieee802154_netdev.h. You have to implement Linux
79net_device, with .type = ARPHRD_IEEE802154. Data is exchanged with socket family
80code via plain sk_buffs. On skb reception skb->cb must contain additional
81info as described in the struct ieee802154_mac_cb. During packet transmission
82the skb->cb is used to provide additional data to device's header_ops->create
83function. Be aware that this data can be overridden later (when socket code
84submits skb to qdisc), so if you need something from that cb later, you should
85store info in the skb->data on your own.
86
87To hook the MLME interface you have to populate the ml_priv field of your
88net_device with a pointer to struct ieee802154_mlme_ops instance. The fields
89assoc_req, assoc_resp, disassoc_req, start_req, and scan_req are optional.
90All other fields are required.
91
92SoftMAC
93-------
94
95The MAC is the middle layer in the IEEE 802.15.4 Linux stack. This moment it
96provides interface for drivers registration and management of slave interfaces.
97
98NOTE: Currently the only monitor device type is supported - it's IEEE 802.15.4
99stack interface for network sniffers (e.g. WireShark).
100
101This layer is going to be extended soon.
102
103See header include/net/mac802154.h and several drivers in
104drivers/net/ieee802154/.
105
106Fake drivers
107------------
108
109In addition there is a driver available which simulates a real device with
110SoftMAC (fakelb - IEEE 802.15.4 loopback driver) interface. This option
111provides a possibility to test and debug the stack without usage of real hardware.
112
113Device drivers API
114==================
115
116The include/net/mac802154.h defines following functions:
117
118.. c:function:: struct ieee802154_dev *ieee802154_alloc_device (size_t priv_size, struct ieee802154_ops *ops)
119
120Allocation of IEEE 802.15.4 compatible device.
121
122.. c:function:: void ieee802154_free_device(struct ieee802154_dev *dev)
123
124Freeing allocated device.
125
126.. c:function:: int ieee802154_register_device(struct ieee802154_dev *dev)
127
128Register PHY in the system.
129
130.. c:function:: void ieee802154_unregister_device(struct ieee802154_dev *dev)
131
132Freeing registered PHY.
133
134.. c:function:: void ieee802154_rx_irqsafe(struct ieee802154_hw *hw, struct sk_buff *skb, u8 lqi):
135
136Telling 802.15.4 module there is a new received frame in the skb with
137the RF Link Quality Indicator (LQI) from the hardware device.
138
139.. c:function:: void ieee802154_xmit_complete(struct ieee802154_hw *hw, struct sk_buff *skb, bool ifs_handling):
140
141Telling 802.15.4 module the frame in the skb is or going to be
142transmitted through the hardware device
143
144The device driver must implement the following callbacks in the IEEE 802.15.4
145operations structure at least::
146
147   struct ieee802154_ops {
148        ...
149        int     (*start)(struct ieee802154_hw *hw);
150        void    (*stop)(struct ieee802154_hw *hw);
151        ...
152        int     (*xmit_async)(struct ieee802154_hw *hw, struct sk_buff *skb);
153        int     (*ed)(struct ieee802154_hw *hw, u8 *level);
154        int     (*set_channel)(struct ieee802154_hw *hw, u8 page, u8 channel);
155        ...
156   };
157
158.. c:function:: int start(struct ieee802154_hw *hw):
159
160Handler that 802.15.4 module calls for the hardware device initialization.
161
162.. c:function:: void stop(struct ieee802154_hw *hw):
163
164Handler that 802.15.4 module calls for the hardware device cleanup.
165
166.. c:function:: int xmit_async(struct ieee802154_hw *hw, struct sk_buff *skb):
167
168Handler that 802.15.4 module calls for each frame in the skb going to be
169transmitted through the hardware device.
170
171.. c:function:: int ed(struct ieee802154_hw *hw, u8 *level):
172
173Handler that 802.15.4 module calls for Energy Detection from the hardware
174device.
175
176.. c:function:: int set_channel(struct ieee802154_hw *hw, u8 page, u8 channel):
177
178Set radio for listening on specific channel of the hardware device.
179
180Moreover IEEE 802.15.4 device operations structure should be filled.
181