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:: 30 31 int sd = socket(PF_IEEE802154, SOCK_DGRAM, 0); 32 33The address family, socket addresses etc. are defined in the 34include/net/af_ieee802154.h header or in the special header 35in the userspace package (see either https://linux-wpan.org/wpan-tools.html 36or the git tree at https://github.com/linux-wpan/wpan-tools). 37 386LoWPAN Linux implementation 39============================ 40 41The IEEE 802.15.4 standard specifies an MTU of 127 bytes, yielding about 80 42octets of actual MAC payload once security is turned on, on a wireless link 43with a link throughput of 250 kbps or less. The 6LoWPAN adaptation format 44[RFC4944] was specified to carry IPv6 datagrams over such constrained links, 45taking into account limited bandwidth, memory, or energy resources that are 46expected in applications such as wireless Sensor Networks. [RFC4944] defines 47a Mesh Addressing header to support sub-IP forwarding, a Fragmentation header 48to support the IPv6 minimum MTU requirement [RFC2460], and stateless header 49compression for IPv6 datagrams (LOWPAN_HC1 and LOWPAN_HC2) to reduce the 50relatively large IPv6 and UDP headers down to (in the best case) several bytes. 51 52In September 2011 the standard update was published - [RFC6282]. 53It deprecates HC1 and HC2 compression and defines IPHC encoding format which is 54used in this Linux implementation. 55 56All the code related to 6lowpan you may find in files: net/6lowpan/* 57and net/ieee802154/6lowpan/* 58 59To setup a 6LoWPAN interface you need: 601. Add IEEE802.15.4 interface and set channel and PAN ID; 612. Add 6lowpan interface by command like: 62# ip link add link wpan0 name lowpan0 type lowpan 633. Bring up 'lowpan0' interface 64 65Drivers 66======= 67 68Like with WiFi, there are several types of devices implementing IEEE 802.15.4. 691) 'HardMAC'. The MAC layer is implemented in the device itself, the device 70exports a management (e.g. MLME) and data API. 712) 'SoftMAC' or just radio. These types of devices are just radio transceivers 72possibly with some kinds of acceleration like automatic CRC computation and 73comparation, automagic ACK handling, address matching, etc. 74 75Those types of devices require different approach to be hooked into Linux kernel. 76 77HardMAC 78------- 79 80See the header include/net/ieee802154_netdev.h. You have to implement Linux 81net_device, with .type = ARPHRD_IEEE802154. Data is exchanged with socket family 82code via plain sk_buffs. On skb reception skb->cb must contain additional 83info as described in the struct ieee802154_mac_cb. During packet transmission 84the skb->cb is used to provide additional data to device's header_ops->create 85function. Be aware that this data can be overridden later (when socket code 86submits skb to qdisc), so if you need something from that cb later, you should 87store info in the skb->data on your own. 88 89To hook the MLME interface you have to populate the ml_priv field of your 90net_device with a pointer to struct ieee802154_mlme_ops instance. The fields 91assoc_req, assoc_resp, disassoc_req, start_req, and scan_req are optional. 92All other fields are required. 93 94SoftMAC 95------- 96 97The MAC is the middle layer in the IEEE 802.15.4 Linux stack. This moment it 98provides interface for drivers registration and management of slave interfaces. 99 100NOTE: Currently the only monitor device type is supported - it's IEEE 802.15.4 101stack interface for network sniffers (e.g. WireShark). 102 103This layer is going to be extended soon. 104 105See header include/net/mac802154.h and several drivers in 106drivers/net/ieee802154/. 107 108Fake drivers 109------------ 110 111In addition there is a driver available which simulates a real device with 112SoftMAC (fakelb - IEEE 802.15.4 loopback driver) interface. This option 113provides a possibility to test and debug the stack without usage of real hardware. 114 115Device drivers API 116================== 117 118The 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 122Allocation of IEEE 802.15.4 compatible device. 123 124.. c:function:: void ieee802154_free_device(struct ieee802154_dev *dev) 125 126Freeing allocated device. 127 128.. c:function:: int ieee802154_register_device(struct ieee802154_dev *dev) 129 130Register PHY in the system. 131 132.. c:function:: void ieee802154_unregister_device(struct ieee802154_dev *dev) 133 134Freeing registered PHY. 135 136.. c:function:: void ieee802154_rx_irqsafe(struct ieee802154_hw *hw, struct sk_buff *skb, u8 lqi) 137 138Telling 802.15.4 module there is a new received frame in the skb with 139the 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 143Telling 802.15.4 module the frame in the skb is or going to be 144transmitted through the hardware device 145 146The device driver must implement the following callbacks in the IEEE 802.15.4 147operations 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 162Handler that 802.15.4 module calls for the hardware device initialization. 163 164.. c:function:: void stop(struct ieee802154_hw *hw) 165 166Handler 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 170Handler that 802.15.4 module calls for each frame in the skb going to be 171transmitted through the hardware device. 172 173.. c:function:: int ed(struct ieee802154_hw *hw, u8 *level) 174 175Handler that 802.15.4 module calls for Energy Detection from the hardware 176device. 177 178.. c:function:: int set_channel(struct ieee802154_hw *hw, u8 page, u8 channel) 179 180Set radio for listening on specific channel of the hardware device. 181 182Moreover IEEE 802.15.4 device operations structure should be filled. 183