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Based on kernel version 3.13. Page generated on 2014-01-20 22:05 EST.

1	Userspace communication protocol over connector [1].
2	
3	
4	Message types.
5	=============
6	
7	There are three types of messages between w1 core and userspace:
8	1. Events. They are generated each time new master or slave device
9		found either due to automatic or requested search.
10	2. Userspace commands.
11	3. Replies to userspace commands.
12	
13	
14	Protocol.
15	========
16	
17	[struct cn_msg] - connector header.
18		Its length field is equal to size of the attached data
19	[struct w1_netlink_msg] - w1 netlink header.
20		__u8 type 	- message type.
21				W1_LIST_MASTERS
22					list current bus masters
23				W1_SLAVE_ADD/W1_SLAVE_REMOVE
24					slave add/remove events
25				W1_MASTER_ADD/W1_MASTER_REMOVE
26					master add/remove events
27				W1_MASTER_CMD
28					userspace command for bus master
29					device (search/alarm search)
30				W1_SLAVE_CMD
31					userspace command for slave device
32					(read/write/touch)
33		__u8 res	- reserved
34		__u16 len	- size of data attached to this header data
35		union {
36			__u8 id[8];			 - slave unique device id
37			struct w1_mst {
38				__u32		id;	 - master's id
39				__u32		res;	 - reserved
40			} mst;
41		} id;
42	
43	[struct w1_netlink_cmd] - command for given master or slave device.
44		__u8 cmd	- command opcode.
45				W1_CMD_READ 	- read command
46				W1_CMD_WRITE	- write command
47				W1_CMD_TOUCH	- touch command
48					(write and sample data back to userspace)
49				W1_CMD_SEARCH	- search command
50				W1_CMD_ALARM_SEARCH - alarm search command
51		__u8 res	- reserved
52		__u16 len	- length of data for this command
53			For read command data must be allocated like for write command
54		__u8 data[0]	- data for this command
55	
56	
57	Each connector message can include one or more w1_netlink_msg with
58	zero or more attached w1_netlink_cmd messages.
59	
60	For event messages there are no w1_netlink_cmd embedded structures,
61	only connector header and w1_netlink_msg strucutre with "len" field
62	being zero and filled type (one of event types) and id:
63	either 8 bytes of slave unique id in host order,
64	or master's id, which is assigned to bus master device
65	when it is added to w1 core.
66	
67	Currently replies to userspace commands are only generated for read
68	command request. One reply is generated exactly for one w1_netlink_cmd
69	read request. Replies are not combined when sent - i.e. typical reply
70	messages looks like the following:
71	
72	[cn_msg][w1_netlink_msg][w1_netlink_cmd]
73	cn_msg.len = sizeof(struct w1_netlink_msg) +
74		     sizeof(struct w1_netlink_cmd) +
75		     cmd->len;
76	w1_netlink_msg.len = sizeof(struct w1_netlink_cmd) + cmd->len;
77	w1_netlink_cmd.len = cmd->len;
78	
79	Replies to W1_LIST_MASTERS should send a message back to the userspace
80	which will contain list of all registered master ids in the following
81	format:
82	
83		cn_msg (CN_W1_IDX.CN_W1_VAL as id, len is equal to sizeof(struct
84		w1_netlink_msg) plus number of masters multiplied by 4)
85		w1_netlink_msg (type: W1_LIST_MASTERS, len is equal to
86			number of masters multiplied by 4 (u32 size))
87		id0 ... idN
88	
89		Each message is at most 4k in size, so if number of master devices
90		exceeds this, it will be split into several messages,
91		cn.seq will be increased for each one.
92	
93	W1 search and alarm search commands.
94	request:
95	[cn_msg]
96	  [w1_netlink_msg type = W1_MASTER_CMD
97	  	id is equal to the bus master id to use for searching]
98	  [w1_netlink_cmd cmd = W1_CMD_SEARCH or W1_CMD_ALARM_SEARCH]
99	
100	reply:
101	  [cn_msg, ack = 1 and increasing, 0 means the last message,
102	  	seq is equal to the request seq]
103	  [w1_netlink_msg type = W1_MASTER_CMD]
104	  [w1_netlink_cmd cmd = W1_CMD_SEARCH or W1_CMD_ALARM_SEARCH
105		len is equal to number of IDs multiplied by 8]
106	  [64bit-id0 ... 64bit-idN]
107	Length in each header corresponds to the size of the data behind it, so
108	w1_netlink_cmd->len = N * 8; where N is number of IDs in this message.
109		Can be zero.
110	w1_netlink_msg->len = sizeof(struct w1_netlink_cmd) + N * 8;
111	cn_msg->len = sizeof(struct w1_netlink_msg) +
112		      sizeof(struct w1_netlink_cmd) +
113		      N*8;
114	
115	W1 reset command.
116	[cn_msg]
117	  [w1_netlink_msg type = W1_MASTER_CMD
118	  	id is equal to the bus master id to use for searching]
119	  [w1_netlink_cmd cmd = W1_CMD_RESET]
120	
121	
122	Command status replies.
123	======================
124	
125	Each command (either root, master or slave with or without w1_netlink_cmd
126	structure) will be 'acked' by the w1 core. Format of the reply is the same
127	as request message except that length parameters do not account for data
128	requested by the user, i.e. read/write/touch IO requests will not contain
129	data, so w1_netlink_cmd.len will be 0, w1_netlink_msg.len will be size
130	of the w1_netlink_cmd structure and cn_msg.len will be equal to the sum
131	of the sizeof(struct w1_netlink_msg) and sizeof(struct w1_netlink_cmd).
132	If reply is generated for master or root command (which do not have
133	w1_netlink_cmd attached), reply will contain only cn_msg and w1_netlink_msg
134	structires.
135	
136	w1_netlink_msg.status field will carry positive error value
137	(EINVAL for example) or zero in case of success.
138	
139	All other fields in every structure will mirror the same parameters in the
140	request message (except lengths as described above).
141	
142	Status reply is generated for every w1_netlink_cmd embedded in the
143	w1_netlink_msg, if there are no w1_netlink_cmd structures,
144	reply will be generated for the w1_netlink_msg.
145	
146	All w1_netlink_cmd command structures are handled in every w1_netlink_msg,
147	even if there were errors, only length mismatch interrupts message processing.
148	
149	
150	Operation steps in w1 core when new command is received.
151	=======================================================
152	
153	When new message (w1_netlink_msg) is received w1 core detects if it is
154	master or slave request, according to w1_netlink_msg.type field.
155	Then master or slave device is searched for.
156	When found, master device (requested or those one on where slave device
157	is found) is locked. If slave command is requested, then reset/select
158	procedure is started to select given device.
159	
160	Then all requested in w1_netlink_msg operations are performed one by one.
161	If command requires reply (like read command) it is sent on command completion.
162	
163	When all commands (w1_netlink_cmd) are processed muster device is unlocked
164	and next w1_netlink_msg header processing started.
165	
166	
167	Connector [1] specific documentation.
168	====================================
169	
170	Each connector message includes two u32 fields as "address".
171	w1 uses CN_W1_IDX and CN_W1_VAL defined in include/linux/connector.h header.
172	Each message also includes sequence and acknowledge numbers.
173	Sequence number for event messages is appropriate bus master sequence number
174	increased with each event message sent "through" this master.
175	Sequence number for userspace requests is set by userspace application.
176	Sequence number for reply is the same as was in request, and
177	acknowledge number is set to seq+1.
178	
179	
180	Additional documantion, source code examples.
181	============================================
182	
183	1. Documentation/connector
184	2. http://www.ioremap.net/archive/w1
185	This archive includes userspace application w1d.c which uses
186	read/write/search commands for all master/slave devices found on the bus.
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