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