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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. Includes read/write and search/alarm search comamnds.
- 3. Replies to userspace commands.
- Protocol.
- ========
- [struct cn_msg] - connector header. It's length field is equal to size of the attached data.
- [struct w1_netlink_msg] - w1 netlink header.
- __u8 type - message type.
- 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/ search/alarm search
- for bus master device where given slave device found).
- __u8 res - reserved
- __u16 len - size of attached to this header data.
- union {
- __u8 id; - slave unique device id
- struct w1_mst {
- __u32 id; - master's id.
- __u32 res; - reserved
- } mst;
- } id;
- [strucrt w1_netlink_cmd] - command for gived master or slave device.
- __u8 cmd - command opcode.
- W1_CMD_READ - read command.
- W1_CMD_WRITE - write command.
- 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 of 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;
- 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 of 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://tservice.net.ru/~s0mbre/archive/w1
- This archive includes userspace application w1d.c which
- uses read/write/search commands for all master/slave devices found on the bus.
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