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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 | ||
ac2dc8ca | 24 | Phonet packets have a common header as follows: |
953f5517 RDC |
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 | ||
ac2dc8ca RDC |
36 | On Linux, the link-layer header includes the pn_media byte (see below). |
37 | The next 7 bytes are part of the network-layer header. | |
38 | ||
19f59460 | 39 | The device ID is split: the 6 higher-order bits constitute the device |
ac2dc8ca RDC |
40 | address, while the 2 lower-order bits are used for multiplexing, as are |
41 | the 8-bit object identifiers. As such, Phonet can be considered as a | |
953f5517 RDC |
42 | network layer with 6 bits of address space and 10 bits for transport |
43 | protocol (much like port numbers in IP world). | |
44 | ||
ac2dc8ca RDC |
45 | The modem always has address number zero. All other device have a their |
46 | own 6-bit address. | |
953f5517 RDC |
47 | |
48 | ||
49 | Link layer | |
50 | ---------- | |
51 | ||
52 | Phonet links are always point-to-point links. The link layer header | |
53 | consists of a single Phonet media type byte. It uniquely identifies the | |
54 | link through which the packet is transmitted, from the modem's | |
ac2dc8ca RDC |
55 | perspective. Each Phonet network device shall prepend and set the media |
56 | type byte as appropriate. For convenience, a common phonet_header_ops | |
57 | link-layer header operations structure is provided. It sets the | |
58 | media type according to the network device hardware address. | |
59 | ||
60 | Linux Phonet network interfaces support a dedicated link layer packets | |
61 | type (ETH_P_PHONET) which is out of the Ethernet type range. They can | |
62 | only send and receive Phonet packets. | |
63 | ||
64 | The virtual TUN tunnel device driver can also be used for Phonet. This | |
65 | requires IFF_TUN mode, _without_ the IFF_NO_PI flag. In this case, | |
66 | there is no link-layer header, so there is no Phonet media type byte. | |
953f5517 RDC |
67 | |
68 | Note that Phonet interfaces are not allowed to re-order packets, so | |
69 | only the (default) Linux FIFO qdisc should be used with them. | |
70 | ||
71 | ||
72 | Network layer | |
73 | ------------- | |
74 | ||
75 | The Phonet socket address family maps the Phonet packet header: | |
76 | ||
77 | struct sockaddr_pn { | |
78 | sa_family_t spn_family; /* AF_PHONET */ | |
79 | uint8_t spn_obj; /* Object ID */ | |
80 | uint8_t spn_dev; /* Device ID */ | |
81 | uint8_t spn_resource; /* Resource or function */ | |
82 | uint8_t spn_zero[...]; /* Padding */ | |
83 | }; | |
84 | ||
85 | The resource field is only used when sending and receiving; | |
86 | It is ignored by bind() and getsockname(). | |
87 | ||
88 | ||
89 | Low-level datagram protocol | |
90 | --------------------------- | |
91 | ||
92 | Applications can send Phonet messages using the Phonet datagram socket | |
93 | protocol from the PF_PHONET family. Each socket is bound to one of the | |
94 | 2^10 object IDs available, and can send and receive packets with any | |
95 | other peer. | |
96 | ||
97 | struct sockaddr_pn addr = { .spn_family = AF_PHONET, }; | |
98 | ssize_t len; | |
99 | socklen_t addrlen = sizeof(addr); | |
100 | int fd; | |
101 | ||
102 | fd = socket(PF_PHONET, SOCK_DGRAM, 0); | |
103 | bind(fd, (struct sockaddr *)&addr, sizeof(addr)); | |
104 | /* ... */ | |
105 | ||
106 | sendto(fd, msg, msglen, 0, (struct sockaddr *)&addr, sizeof(addr)); | |
107 | len = recvfrom(fd, buf, sizeof(buf), 0, | |
108 | (struct sockaddr *)&addr, &addrlen); | |
109 | ||
110 | This protocol follows the SOCK_DGRAM connection-less semantics. | |
111 | However, connect() and getpeername() are not supported, as they did | |
112 | not seem useful with Phonet usages (could be added easily). | |
113 | ||
114 | ||
274a517e RDC |
115 | Resource subscription |
116 | --------------------- | |
117 | ||
118 | A Phonet datagram socket can be subscribed to any number of 8-bits | |
119 | Phonet resources, as follow: | |
120 | ||
121 | uint32_t res = 0xXX; | |
122 | ioctl(fd, SIOCPNADDRESOURCE, &res); | |
123 | ||
124 | Subscription is similarly cancelled using the SIOCPNDELRESOURCE I/O | |
125 | control request, or when the socket is closed. | |
126 | ||
127 | Note that no more than one socket can be subcribed to any given | |
128 | resource at a time. If not, ioctl() will return EBUSY. | |
129 | ||
130 | ||
95430c0b RDC |
131 | Phonet Pipe protocol |
132 | -------------------- | |
133 | ||
134 | The Phonet Pipe protocol is a simple sequenced packets protocol | |
135 | with end-to-end congestion control. It uses the passive listening | |
136 | socket paradigm. The listening socket is bound to an unique free object | |
137 | ID. Each listening socket can handle up to 255 simultaneous | |
138 | connections, one per accept()'d socket. | |
139 | ||
140 | int lfd, cfd; | |
141 | ||
142 | lfd = socket(PF_PHONET, SOCK_SEQPACKET, PN_PROTO_PIPE); | |
143 | listen (lfd, INT_MAX); | |
144 | ||
145 | /* ... */ | |
146 | cfd = accept(lfd, NULL, NULL); | |
147 | for (;;) | |
148 | { | |
149 | char buf[...]; | |
150 | ssize_t len = read(cfd, buf, sizeof(buf)); | |
151 | ||
152 | /* ... */ | |
153 | ||
154 | write(cfd, msg, msglen); | |
155 | } | |
156 | ||
157 | Connections are established between two endpoints by a "third party" | |
158 | application. This means that both endpoints are passive; so connect() | |
159 | is not possible. | |
160 | ||
161 | WARNING: | |
162 | When polling a connected pipe socket for writability, there is an | |
163 | intrinsic race condition whereby writability might be lost between the | |
164 | polling and the writing system calls. In this case, the socket will | |
3497b2f2 RM |
165 | block until write becomes possible again, unless non-blocking mode |
166 | is enabled. | |
95430c0b RDC |
167 | |
168 | ||
169 | The pipe protocol provides two socket options at the SOL_PNPIPE level: | |
170 | ||
171 | PNPIPE_ENCAP accepts one integer value (int) of: | |
172 | ||
173 | PNPIPE_ENCAP_NONE: The socket operates normally (default). | |
174 | ||
175 | PNPIPE_ENCAP_IP: The socket is used as a backend for a virtual IP | |
176 | interface. This requires CAP_NET_ADMIN capability. GPRS data | |
177 | support on Nokia modems can use this. Note that the socket cannot | |
178 | be reliably poll()'d or read() from while in this mode. | |
179 | ||
180 | PNPIPE_IFINDEX is a read-only integer value. It contains the | |
181 | interface index of the network interface created by PNPIPE_ENCAP, | |
182 | or zero if encapsulation is off. | |
183 | ||
acaf7df6 RDC |
184 | PNPIPE_HANDLE is a read-only integer value. It contains the underlying |
185 | identifier ("pipe handle") of the pipe. This is only defined for | |
186 | socket descriptors that are already connected or being connected. | |
187 | ||
95430c0b | 188 | |
4d443a08 KS |
189 | Phonet Pipe-controller Implementation |
190 | ------------------------------------- | |
191 | ||
192 | Phonet Pipe-controller is enabled by selecting the CONFIG_PHONET_PIPECTRLR Kconfig | |
193 | option. It is useful when communicating with those Nokia Modems which do not | |
194 | implement Pipe controller in them e.g. Nokia Slim Modem used in ST-Ericsson | |
195 | U8500 platform. | |
196 | ||
197 | The implementation is based on the Data Connection Establishment Sequence | |
198 | depicted in 'Nokia Wireless Modem API - Wireless_modem_user_guide.pdf' | |
199 | document. | |
200 | ||
201 | It allows a phonet sequenced socket (host-pep) to initiate a Pipe connection | |
202 | between itself and a remote pipe-end point (e.g. modem). | |
203 | ||
204 | The implementation adds socket options at SOL_PNPIPE level: | |
205 | ||
03789f26 RDC |
206 | PNPIPE_ENABLE accepts one integer value (int). If set to zero, the pipe |
207 | is disabled. If the value is non-zero, the pipe is enabled. If the pipe | |
208 | is not (yet) connected, ENOTCONN is error is returned. | |
4d443a08 | 209 | |
f20ce779 KS |
210 | The implementation also adds socket 'connect'. On calling the 'connect', pipe |
211 | will be created between the source socket and the destination, and the pipe | |
212 | state will be set to PIPE_DISABLED. | |
4d443a08 | 213 | |
4d443a08 KS |
214 | After a pipe has been created and enabled successfully, the Pipe data can be |
215 | exchanged between the host-pep and remote-pep (modem). | |
216 | ||
f20ce779 KS |
217 | User-space would typically follow below sequence with Pipe controller:- |
218 | -socket | |
219 | -bind | |
220 | -setsockopt for PNPIPE_PIPE_HANDLE | |
221 | -connect | |
222 | -setsockopt for PNPIPE_ENCAP_IP | |
223 | -setsockopt for PNPIPE_ENABLE | |
224 | ||
225 | ||
953f5517 RDC |
226 | Authors |
227 | ------- | |
228 | ||
229 | Linux Phonet was initially written by Sakari Ailus. | |
230 | Other contributors include Mikä Liljeberg, Andras Domokos, | |
231 | Carlos Chinea and Rémi Denis-Courmont. | |
232 | Copyright (C) 2008 Nokia Corporation. |