W1: Dallas’ 1-wire bus¶
- Author:
- David Fries 
W1 API internal to the kernel¶
include/linux/w1.h¶
W1 kernel API functions.
- 
struct w1_reg_num¶
- broken out slave device id 
Definition:
struct w1_reg_num {
#if defined(__LITTLE_ENDIAN_BITFIELD);
    __u64 family:8,id:48, crc:8;
#elif defined(__BIG_ENDIAN_BITFIELD);
    __u64 crc:8,id:48, family:8;
#else;
#error "Please fix <asm/byteorder.h>";
#endif;
};
Members
- family
- identifies the type of device 
- id
- along with family is the unique device id 
- crc
- checksum of the other bytes 
- crc
- checksum of the other bytes 
- id
- along with family is the unique device id 
- family
- identifies the type of device 
- 
struct w1_slave¶
- holds a single slave device on the bus 
Definition:
struct w1_slave {
    struct module           *owner;
    unsigned char           name[W1_MAXNAMELEN];
    struct list_head        w1_slave_entry;
    struct w1_reg_num       reg_num;
    atomic_t refcnt;
    int ttl;
    unsigned long           flags;
    struct w1_master        *master;
    struct w1_family        *family;
    void *family_data;
    struct device           dev;
    struct device           *hwmon;
};
Members
- owner
- Points to the one wire “wire” kernel module. 
- name
- Device id is ascii. 
- w1_slave_entry
- data for the linked list 
- reg_num
- the slave id in binary 
- refcnt
- reference count, delete when 0 
- ttl
- decrement per search this slave isn’t found, deatch at 0 
- flags
- bit flags for W1_SLAVE_ACTIVE W1_SLAVE_DETACH 
- master
- bus which this slave is on 
- family
- module for device family type 
- family_data
- pointer for use by the family module 
- dev
- kernel device identifier 
- hwmon
- pointer to hwmon device 
- 
struct w1_bus_master¶
- operations available on a bus master 
Definition:
struct w1_bus_master {
    void *data;
    u8 (*read_bit)(void *);
    void (*write_bit)(void *, u8);
    u8 (*touch_bit)(void *, u8);
    u8 (*read_byte)(void *);
    void (*write_byte)(void *, u8);
    u8 (*read_block)(void *, u8 *, int);
    void (*write_block)(void *, const u8 *, int);
    u8 (*triplet)(void *, u8);
    u8 (*reset_bus)(void *);
    u8 (*set_pullup)(void *, int);
    void (*search)(void *, struct w1_master *, u8, w1_slave_found_callback);
    char *dev_id;
};
Members
- data
- the first parameter in all the functions below 
- read_bit
- Sample the line level return the level read (0 or 1) 
- write_bit
- Sets the line level 
- touch_bit
- the lowest-level function for devices that really support the 1-wire protocol. touch_bit(0) = write-0 cycle touch_bit(1) = write-1 / read cycle return the bit read (0 or 1) 
- read_byte
- Reads a byte. Same as 8 touch_bit(1) calls. return the byte read 
- write_byte
- Writes a byte. Same as 8 touch_bit(x) calls. 
- read_block
- Same as a series of read_byte() calls return the number of bytes read 
- write_block
- Same as a series of write_byte() calls 
- triplet
- Combines two reads and a smart write for ROM searches return bit0=Id bit1=comp_id bit2=dir_taken 
- reset_bus
- long write-0 with a read for the presence pulse detection return -1=Error, 0=Device present, 1=No device present 
- set_pullup
- Put out a strong pull-up pulse of the specified duration. return -1=Error, 0=completed 
- search
- Really nice hardware can handle the different types of ROM search w1_master* is passed to the slave found callback. u8 is search_type, W1_SEARCH or W1_ALARM_SEARCH 
- dev_id
- Optional device id string, which w1 slaves could use for creating names, which then give a connection to the w1 master 
Note
read_bit and write_bit are very low level functions and should only be used with hardware that doesn’t really support 1-wire operations, like a parallel/serial port. Either define read_bit and write_bit OR define, at minimum, touch_bit and reset_bus.
- 
enum w1_master_flags¶
- bitfields used in w1_master.flags 
Constants
- W1_ABORT_SEARCH
- abort searching early on shutdown 
- W1_WARN_MAX_COUNT
- limit warning when the maximum count is reached 
- 
struct w1_master¶
- one per bus master 
Definition:
struct w1_master {
    struct list_head        w1_master_entry;
    struct module           *owner;
    unsigned char           name[W1_MAXNAMELEN];
    struct mutex            list_mutex;
    struct list_head        slist;
    struct list_head        async_list;
    int max_slave_count, slave_count;
    unsigned long           attempts;
    int slave_ttl;
    int initialized;
    u32 id;
    int search_count;
    u64 search_id;
    atomic_t refcnt;
    void *priv;
    int enable_pullup;
    int pullup_duration;
    long flags;
    struct task_struct      *thread;
    struct mutex            mutex;
    struct mutex            bus_mutex;
    struct device_driver    *driver;
    struct device           dev;
    struct w1_bus_master    *bus_master;
    u32 seq;
};
Members
- w1_master_entry
- master linked list 
- owner
- module owner 
- name
- dynamically allocate bus name 
- list_mutex
- protect slist and async_list 
- slist
- linked list of slaves 
- async_list
- linked list of netlink commands to execute 
- max_slave_count
- maximum number of slaves to search for at a time 
- slave_count
- current number of slaves known 
- attempts
- number of searches ran 
- slave_ttl
- number of searches before a slave is timed out 
- initialized
- prevent init/removal race conditions 
- id
- w1 bus number 
- search_count
- number of automatic searches to run, -1 unlimited 
- search_id
- allows continuing a search 
- refcnt
- reference count 
- priv
- private data storage 
- enable_pullup
- allows a strong pullup 
- pullup_duration
- time for the next strong pullup 
- flags
- one of w1_master_flags 
- thread
- thread for bus search and netlink commands 
- mutex
- protect most of w1_master 
- bus_mutex
- pretect concurrent bus access 
- driver
- sysfs driver 
- dev
- sysfs device 
- bus_master
- io operations available 
- seq
- sequence number used for netlink broadcasts 
- 
struct w1_family_ops¶
- operations for a family type 
Definition:
struct w1_family_ops {
    int (*add_slave)(struct w1_slave *sl);
    void (*remove_slave)(struct w1_slave *sl);
    const struct attribute_group **groups;
    const struct hwmon_chip_info *chip_info;
};
Members
- add_slave
- add_slave 
- remove_slave
- remove_slave 
- groups
- sysfs group 
- chip_info
- pointer to struct hwmon_chip_info 
- 
struct w1_family¶
- reference counted family structure. 
Definition:
struct w1_family {
    struct list_head        family_entry;
    u8 fid;
    const struct w1_family_ops *fops;
    const struct of_device_id *of_match_table;
    atomic_t refcnt;
};
Members
- family_entry
- family linked list 
- fid
- 8 bit family identifier 
- fops
- operations for this family 
- of_match_table
- open firmware match table 
- refcnt
- reference counter 
- 
module_w1_family¶
module_w1_family (__w1_family)
Helper macro for registering a 1-Wire families
Parameters
- __w1_family
- w1_family struct 
Description
Helper macro for 1-Wire families which do not do anything special in module
init/exit. This eliminates a lot of boilerplate. Each module may only
use this macro once, and calling it replaces module_init() and module_exit()
drivers/w1/w1.c¶
W1 core functions.
- 
void w1_search(struct w1_master *dev, u8 search_type, w1_slave_found_callback cb)¶
- Performs a ROM Search & registers any devices found. 
Parameters
- struct w1_master *dev
- The master device to search 
- u8 search_type
- W1_SEARCH to search all devices, or W1_ALARM_SEARCH to return only devices in the alarmed state 
- w1_slave_found_callback cb
- Function to call when a device is found 
Description
The 1-wire search is a simple binary tree search. For each bit of the address, we read two bits and write one bit. The bit written will put to sleep all devies that don’t match that bit. When the two reads differ, the direction choice is obvious. When both bits are 0, we must choose a path to take. When we can scan all 64 bits without having to choose a path, we are done.
See “Application note 187 1-wire search algorithm” at www.maxim-ic.com
Parameters
- struct w1_master *dev
- w1_master device 
Description
The w1 master list_mutex must be held.
Return
1 if there were commands to executed 0 otherwise
drivers/w1/w1_family.c¶
Allows registering device family operations.
Parameters
- struct w1_family *newf
- family to register 
Parameters
- struct w1_family *fent
- family to unregister 
drivers/w1/w1_internal.h¶
W1 internal initialization for master devices.
- 
struct w1_async_cmd¶
- execute callback from the w1_process kthread 
Definition:
struct w1_async_cmd {
    struct list_head        async_entry;
    void (*cb)(struct w1_master *dev, struct w1_async_cmd *async_cmd);
};
Members
- async_entry
- link entry 
- cb
- callback function, must list_del and destroy this list before returning 
Description
When inserted into the w1_master async_list, w1_process will execute the callback. Embed this into the structure with the command details.
drivers/w1/w1_int.c¶
W1 internal initialization for master devices.
- 
int w1_add_master_device(struct w1_bus_master *master)¶
- registers a new master device 
Parameters
- struct w1_bus_master *master
- master bus device to register 
- 
void w1_remove_master_device(struct w1_bus_master *bm)¶
- unregister a master device 
Parameters
- struct w1_bus_master *bm
- master bus device to remove 
drivers/w1/w1_netlink.h¶
W1 external netlink API structures and commands.
- 
enum w1_cn_msg_flags¶
- bitfield flags for struct cn_msg.flags 
Constants
- W1_CN_BUNDLE
- Request bundling replies into fewer messagse. Be prepared to handle multiple struct cn_msg, - struct w1_netlink_msg, and- struct w1_netlink_cmdin one packet.
- 
enum w1_netlink_message_types¶
- message type 
Constants
- W1_SLAVE_ADD
- notification that a slave device was added 
- W1_SLAVE_REMOVE
- notification that a slave device was removed 
- W1_MASTER_ADD
- notification that a new bus master was added 
- W1_MASTER_REMOVE
- notification that a bus masterwas removed 
- W1_MASTER_CMD
- initiate operations on a specific master 
- W1_SLAVE_CMD
- sends reset, selects the slave, then does a read/write/touch operation 
- W1_LIST_MASTERS
- used to determine the bus master identifiers 
- 
struct w1_netlink_msg¶
- holds w1 message type, id, and result 
Definition:
struct w1_netlink_msg {
    __u8 type;
    __u8 status;
    __u16 len;
    union {
        __u8 id[8];
        struct w1_mst {
            __u32 id;
            __u32 res;
        } mst;
    } id;
    __u8 data[];
};
Members
- type
- status
- kernel feedback for success 0 or errno failure value 
- len
- length of data following w1_netlink_msg 
- id
- union holding bus master id (msg.id) and slave device id (id[8]). 
- id.id
- Slave ID (8 bytes) 
- id.mst
- bus master identification 
- id.mst.id
- bus master ID 
- id.mst.res
- bus master reserved 
- data
- start address of any following data 
Description
The base message structure for w1 messages over netlink.
The netlink connector data sequence is, struct nlmsghdr, struct cn_msg,
then one or more struct w1_netlink_msg (each with optional data).
- 
enum w1_commands¶
- commands available for master or slave operations 
Constants
- W1_CMD_READ
- read len bytes 
- W1_CMD_WRITE
- write len bytes 
- W1_CMD_SEARCH
- initiate a standard search, returns only the slave devices found during that search 
- W1_CMD_ALARM_SEARCH
- search for devices that are currently alarming 
- W1_CMD_TOUCH
- Touches a series of bytes. 
- W1_CMD_RESET
- sends a bus reset on the given master 
- W1_CMD_SLAVE_ADD
- adds a slave to the given master, 8 byte slave id at data[0] 
- W1_CMD_SLAVE_REMOVE
- removes a slave to the given master, 8 byte slave id at data[0] 
- W1_CMD_LIST_SLAVES
- list of slaves registered on this master 
- W1_CMD_MAX
- number of available commands 
- 
struct w1_netlink_cmd¶
- holds the command and data 
Definition:
struct w1_netlink_cmd {
    __u8 cmd;
    __u8 res;
    __u16 len;
    __u8 data[];
};
Members
- cmd
- one of - enum w1_commands
- res
- reserved 
- len
- length of data following w1_netlink_cmd 
- data
- start address of any following data 
Description
One or more struct w1_netlink_cmd is placed starting at w1_netlink_msg.data
each with optional data.
drivers/w1/w1_io.c¶
W1 input/output.
- 
u8 w1_touch_bit(struct w1_master *dev, int bit)¶
- Generates a write-0 or write-1 cycle and samples the level. 
Parameters
- struct w1_master *dev
- the master device 
- int bit
- 0 - write a 0, 1 - write a 0 read the level 
Parameters
- struct w1_master *dev
- the master device 
- u8 byte
- the byte to write 
Parameters
- struct w1_master *dev
- the master device 
- int bdir
- the bit to write if both id_bit and comp_bit are 0 
Description
- Return bits:
- bit 0 = id_bit bit 1 = comp_bit bit 2 = dir_taken 
If both bits 0 & 1 are set, the search should be restarted.
Return
bit fields - see above
Parameters
- struct w1_master *dev
- the master device 
Return
the byte read
Parameters
- struct w1_master *dev
- the master device 
- const u8 *buf
- pointer to the data to write 
- int len
- the number of bytes to write 
Parameters
- struct w1_master *dev
- the master device 
- u8 *buf
- pointer to the data to write 
- int len
- the number of bytes to write 
Parameters
- struct w1_master *dev
- the master device 
- u8 *buf
- pointer to the buffer to fill 
- int len
- the number of bytes to read 
Return
the number of bytes read
Parameters
- struct w1_master *dev
- the master device 
Return
0=Device present, 1=No device present or error
Parameters
- struct w1_slave *sl
- the slave to select 
Description
Resets the bus and then selects the slave by sending either a skip rom or a rom match. A skip rom is issued if there is only one device registered on the bus. The w1 master lock must be held.
Return
0=success, anything else=error
Parameters
- struct w1_master *dev
- the master device 
Description
When the workflow with a slave amongst many requires several successive commands a reset between each, this function is similar to doing a reset then a match ROM for the last matched ROM. The advantage being that the matched ROM step is skipped in favor of the resume command. The slave must support the command of course.
If the bus has only one slave, traditionnaly the match ROM is skipped and a “SKIP ROM” is done for efficiency. On multi-slave busses, this doesn’t work of course, but the resume command is the next best thing.
The w1 master lock must be held.
Parameters
- struct w1_master *dev
- the master device 
- int delay
- time in milliseconds 
Description
Put out a strong pull-up of the specified duration after the next write operation. Not all hardware supports strong pullups. Hardware that doesn’t support strong pullups will sleep for the given time after the write operation without a strong pullup. This is a one shot request for the next write, specifying zero will clear a previous request. The w1 master lock must be held.
Return
0=success, anything else=error
Parameters
- struct w1_master *dev
- the master device 
- int bit
- bit to write 
Description
Only call if dev->bus_master->touch_bit is NULL
Parameters
- struct w1_master *dev
- the master device 
Description
Pre-write operation, currently only supporting strong pullups. Program the hardware for a strong pullup, if one has been requested and the hardware supports it.
Parameters
- struct w1_master *dev
- the master device 
Description
Post-write operation, currently only supporting strong pullups. If a strong pullup was requested, clear it if the hardware supports them, or execute the delay otherwise, in either case clear the request.
Parameters
- struct w1_master *dev
- the master device 
Description
Only call if dev->bus_master->touch_bit is NULL