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-Userspace communication protocol over connector [1].
-
-
-Message types.
-=============
-
-There are three types of messages between w1 core and userspace:
-1. Events. They are generated each time new master or slave device
- found either due to automatic or requested search.
-2. Userspace commands.
-3. Replies to userspace commands.
-
-
-Protocol.
-========
-
-[struct cn_msg] - connector header.
- Its length field is equal to size of the attached data
-[struct w1_netlink_msg] - w1 netlink header.
- __u8 type - message type.
- W1_LIST_MASTERS
- list current bus masters
- W1_SLAVE_ADD/W1_SLAVE_REMOVE
- slave add/remove events
- W1_MASTER_ADD/W1_MASTER_REMOVE
- master add/remove events
- W1_MASTER_CMD
- userspace command for bus master
- device (search/alarm search)
- W1_SLAVE_CMD
- userspace command for slave device
- (read/write/touch)
- __u8 res - reserved
- __u16 len - size of data attached to this header data
- union {
- __u8 id[8]; - slave unique device id
- struct w1_mst {
- __u32 id; - master's id
- __u32 res; - reserved
- } mst;
- } id;
-
-[struct w1_netlink_cmd] - command for given master or slave device.
- __u8 cmd - command opcode.
- W1_CMD_READ - read command
- W1_CMD_WRITE - write command
- W1_CMD_TOUCH - touch command
- (write and sample data back to userspace)
- W1_CMD_SEARCH - search command
- W1_CMD_ALARM_SEARCH - alarm search command
- __u8 res - reserved
- __u16 len - length of data for this command
- For read command data must be allocated like for write command
- __u8 data[0] - data for this command
-
-
-Each connector message can include one or more w1_netlink_msg with
-zero or more attached w1_netlink_cmd messages.
-
-For event messages there are no w1_netlink_cmd embedded structures,
-only connector header and w1_netlink_msg strucutre with "len" field
-being zero and filled type (one of event types) and id:
-either 8 bytes of slave unique id in host order,
-or master's id, which is assigned to bus master device
-when it is added to w1 core.
-
-Currently replies to userspace commands are only generated for read
-command request. One reply is generated exactly for one w1_netlink_cmd
-read request. Replies are not combined when sent - i.e. typical reply
-messages looks like the following:
-
-[cn_msg][w1_netlink_msg][w1_netlink_cmd]
-cn_msg.len = sizeof(struct w1_netlink_msg) +
- sizeof(struct w1_netlink_cmd) +
- cmd->len;
-w1_netlink_msg.len = sizeof(struct w1_netlink_cmd) + cmd->len;
-w1_netlink_cmd.len = cmd->len;
-
-Replies to W1_LIST_MASTERS should send a message back to the userspace
-which will contain list of all registered master ids in the following
-format:
-
- cn_msg (CN_W1_IDX.CN_W1_VAL as id, len is equal to sizeof(struct
- w1_netlink_msg) plus number of masters multiplied by 4)
- w1_netlink_msg (type: W1_LIST_MASTERS, len is equal to
- number of masters multiplied by 4 (u32 size))
- id0 ... idN
-
- Each message is at most 4k in size, so if number of master devices
- exceeds this, it will be split into several messages,
- cn.seq will be increased for each one.
-
-W1 search and alarm search commands.
-request:
-[cn_msg]
- [w1_netlink_msg type = W1_MASTER_CMD
- id is equal to the bus master id to use for searching]
- [w1_netlink_cmd cmd = W1_CMD_SEARCH or W1_CMD_ALARM_SEARCH]
-
-reply:
- [cn_msg, ack = 1 and increasing, 0 means the last message,
- seq is equal to the request seq]
- [w1_netlink_msg type = W1_MASTER_CMD]
- [w1_netlink_cmd cmd = W1_CMD_SEARCH or W1_CMD_ALARM_SEARCH
- len is equal to number of IDs multiplied by 8]
- [64bit-id0 ... 64bit-idN]
-Length in each header corresponds to the size of the data behind it, so
-w1_netlink_cmd->len = N * 8; where N is number of IDs in this message.
- Can be zero.
-w1_netlink_msg->len = sizeof(struct w1_netlink_cmd) + N * 8;
-cn_msg->len = sizeof(struct w1_netlink_msg) +
- sizeof(struct w1_netlink_cmd) +
- N*8;
-
-W1 reset command.
-[cn_msg]
- [w1_netlink_msg type = W1_MASTER_CMD
- id is equal to the bus master id to use for searching]
- [w1_netlink_cmd cmd = W1_CMD_RESET]
-
-
-Command status replies.
-======================
-
-Each command (either root, master or slave with or without w1_netlink_cmd
-structure) will be 'acked' by the w1 core. Format of the reply is the same
-as request message except that length parameters do not account for data
-requested by the user, i.e. read/write/touch IO requests will not contain
-data, so w1_netlink_cmd.len will be 0, w1_netlink_msg.len will be size
-of the w1_netlink_cmd structure and cn_msg.len will be equal to the sum
-of the sizeof(struct w1_netlink_msg) and sizeof(struct w1_netlink_cmd).
-If reply is generated for master or root command (which do not have
-w1_netlink_cmd attached), reply will contain only cn_msg and w1_netlink_msg
-structires.
-
-w1_netlink_msg.status field will carry positive error value
-(EINVAL for example) or zero in case of success.
-
-All other fields in every structure will mirror the same parameters in the
-request message (except lengths as described above).
-
-Status reply is generated for every w1_netlink_cmd embedded in the
-w1_netlink_msg, if there are no w1_netlink_cmd structures,
-reply will be generated for the w1_netlink_msg.
-
-All w1_netlink_cmd command structures are handled in every w1_netlink_msg,
-even if there were errors, only length mismatch interrupts message processing.
-
-
-Operation steps in w1 core when new command is received.
-=======================================================
-
-When new message (w1_netlink_msg) is received w1 core detects if it is
-master or slave request, according to w1_netlink_msg.type field.
-Then master or slave device is searched for.
-When found, master device (requested or those one on where slave device
-is found) is locked. If slave command is requested, then reset/select
-procedure is started to select given device.
-
-Then all requested in w1_netlink_msg operations are performed one by one.
-If command requires reply (like read command) it is sent on command completion.
-
-When all commands (w1_netlink_cmd) are processed muster device is unlocked
-and next w1_netlink_msg header processing started.
-
-
-Connector [1] specific documentation.
-====================================
-
-Each connector message includes two u32 fields as "address".
-w1 uses CN_W1_IDX and CN_W1_VAL defined in include/linux/connector.h header.
-Each message also includes sequence and acknowledge numbers.
-Sequence number for event messages is appropriate bus master sequence number
-increased with each event message sent "through" this master.
-Sequence number for userspace requests is set by userspace application.
-Sequence number for reply is the same as was in request, and
-acknowledge number is set to seq+1.
-
-
-Additional documantion, source code examples.
-============================================
-
-1. Documentation/connector
-2. http://www.ioremap.net/archive/w1
-This archive includes userspace application w1d.c which uses
-read/write/search commands for all master/slave devices found on the bus.