projects / deliverable / linux.git / blame
| Commit | Line | Data |
|---|---|---|
| 953f5517 RDC |
1 | Linux Phonet protocol family |
| 2 | ============================ | |
| 3 | ||
| 4 | Introduction | |
| 5 | ------------ | |
| 6 | ||
| 7 | Phonet is a packet protocol used by Nokia cellular modems for both IPC | |
| 8 | and RPC. With the Linux Phonet socket family, Linux host processes can | |
| 9 | receive and send messages from/to the modem, or any other external | |
| 10 | device attached to the modem. The modem takes care of routing. | |
| 11 | ||
| 12 | Phonet packets can be exchanged through various hardware connections | |
| 13 | depending on the device, such as: | |
| 14 | - USB with the CDC Phonet interface, | |
| 15 | - infrared, | |
| 16 | - Bluetooth, | |
| 17 | - an RS232 serial port (with a dedicated "FBUS" line discipline), | |
| 18 | - the SSI bus with some TI OMAP processors. | |
| 19 | ||
| 20 | ||
| 21 | Packets format | |
| 22 | -------------- | |
| 23 | ||
| 24 | Phonet packet have a common header as follow: | |
| 25 | ||
| 26 | struct phonethdr { | |
| 27 | uint8_t pn_media; /* Media type (link-layer identifier) */ | |
| 28 | uint8_t pn_rdev; /* Receiver device ID */ | |
| 29 | uint8_t pn_sdev; /* Sender device ID */ | |
| 30 | uint8_t pn_res; /* Resource ID or function */ | |
| 31 | uint16_t pn_length; /* Big-endian message byte length (minus 6) */ | |
| 32 | uint8_t pn_robj; /* Receiver object ID */ | |
| 33 | uint8_t pn_sobj; /* Sender object ID */ | |
| 34 | }; | |
| 35 | ||
| 36 | The device ID is split: the 6 higher order bits consitutes the device | |
| 37 | address, while the 2 lower order bits are used for multiplexing, as are | |
| 38 | the 8-bits object identifiers. As such, Phonet can be considered as a | |
| 39 | network layer with 6 bits of address space and 10 bits for transport | |
| 40 | protocol (much like port numbers in IP world). | |
| 41 | ||
| 42 | The modem always has address number zero. Each other device has a its | |
| 43 | own 6-bits address. | |
| 44 | ||
| 45 | ||
| 46 | Link layer | |
| 47 | ---------- | |
| 48 | ||
| 49 | Phonet links are always point-to-point links. The link layer header | |
| 50 | consists of a single Phonet media type byte. It uniquely identifies the | |
| 51 | link through which the packet is transmitted, from the modem's | |
| 52 | perspective. | |
| 53 | ||
| 54 | Linux Phonet network interfaces use a dedicated link layer type | |
| 55 | (ETH_P_PHONET) which is out of the Ethernet type range. They can only | |
| 56 | send and receive Phonet packets. | |
| 57 | ||
| 58 | Note that Phonet interfaces are not allowed to re-order packets, so | |
| 59 | only the (default) Linux FIFO qdisc should be used with them. | |
| 60 | ||
| 61 | ||
| 62 | Network layer | |
| 63 | ------------- | |
| 64 | ||
| 65 | The Phonet socket address family maps the Phonet packet header: | |
| 66 | ||
| 67 | struct sockaddr_pn { | |
| 68 | sa_family_t spn_family; /* AF_PHONET */ | |
| 69 | uint8_t spn_obj; /* Object ID */ | |
| 70 | uint8_t spn_dev; /* Device ID */ | |
| 71 | uint8_t spn_resource; /* Resource or function */ | |
| 72 | uint8_t spn_zero[...]; /* Padding */ | |
| 73 | }; | |
| 74 | ||
| 75 | The resource field is only used when sending and receiving; | |
| 76 | It is ignored by bind() and getsockname(). | |
| 77 | ||
| 78 | ||
| 79 | Low-level datagram protocol | |
| 80 | --------------------------- | |
| 81 | ||
| 82 | Applications can send Phonet messages using the Phonet datagram socket | |
| 83 | protocol from the PF_PHONET family. Each socket is bound to one of the | |
| 84 | 2^10 object IDs available, and can send and receive packets with any | |
| 85 | other peer. | |
| 86 | ||
| 87 | struct sockaddr_pn addr = { .spn_family = AF_PHONET, }; | |
| 88 | ssize_t len; | |
| 89 | socklen_t addrlen = sizeof(addr); | |
| 90 | int fd; | |
| 91 | ||
| 92 | fd = socket(PF_PHONET, SOCK_DGRAM, 0); | |
| 93 | bind(fd, (struct sockaddr *)&addr, sizeof(addr)); | |
| 94 | /* ... */ | |
| 95 | ||
| 96 | sendto(fd, msg, msglen, 0, (struct sockaddr *)&addr, sizeof(addr)); | |
| 97 | len = recvfrom(fd, buf, sizeof(buf), 0, | |
| 98 | (struct sockaddr *)&addr, &addrlen); | |
| 99 | ||
| 100 | This protocol follows the SOCK_DGRAM connection-less semantics. | |
| 101 | However, connect() and getpeername() are not supported, as they did | |
| 102 | not seem useful with Phonet usages (could be added easily). | |
| 103 | ||
| 104 | ||
| 105 | Authors | |
| 106 | ------- | |
| 107 | ||
| 108 | Linux Phonet was initially written by Sakari Ailus. | |
| 109 | Other contributors include Mikä Liljeberg, Andras Domokos, | |
| 110 | Carlos Chinea and Rémi Denis-Courmont. | |
| 111 | Copyright (C) 2008 Nokia Corporation. |