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Based on kernel version 3.9. Page generated on 2013-05-02 23:17 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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