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

int w1_process_callbacks(struct w1_master *dev)¶: execute each dev->async_list callback entry

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.

int w1_register_family(struct w1_family *newf)¶: register a device family driver

Parameters

struct w1_family *newf: family to register

void w1_unregister_family(struct w1_family *fent)¶: unregister a device family driver

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_cmd in 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: one of enum w1_netlink_message_types
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

void w1_write_8(struct w1_master *dev, u8 byte)¶: Writes 8 bits.

Parameters

struct w1_master *dev: the master device
u8 byte: the byte to write

u8 w1_triplet(struct w1_master *dev, int bdir)¶

Does a triplet - used for searching ROM addresses.

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

u8 w1_read_8(struct w1_master *dev)¶: Reads 8 bits.

Parameters

struct w1_master *dev: the master device

Return

the byte read

void w1_write_block(struct w1_master *dev, const u8 *buf, int len)¶: Writes a series of bytes.

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

void w1_touch_block(struct w1_master *dev, u8 *buf, int len)¶: Touches a series of bytes.

Parameters

struct w1_master *dev: the master device
u8 *buf: pointer to the data to write
int len: the number of bytes to write

u8 w1_read_block(struct w1_master *dev, u8 *buf, int len)¶: Reads a series of bytes.

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

int w1_reset_bus(struct w1_master *dev)¶: Issues a reset bus sequence.

Parameters

struct w1_master *dev: the master device

Return

0=Device present, 1=No device present or error

int w1_reset_select_slave(struct w1_slave *sl)¶: reset and select a slave

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

int w1_reset_resume_command(struct w1_master *dev)¶: resume instead of another match ROM

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.

void w1_next_pullup(struct w1_master *dev, int delay)¶: register for a strong pullup

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

void w1_write_bit(struct w1_master *dev, int bit)¶: Generates a write-0 or write-1 cycle.

Parameters

struct w1_master *dev: the master device
int bit: bit to write

Description

Only call if dev->bus_master->touch_bit is NULL

void w1_pre_write(struct w1_master *dev)¶: pre-write operations

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.

void w1_post_write(struct w1_master *dev)¶: post-write options

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.

u8 w1_read_bit(struct w1_master *dev)¶: Generates a write-1 cycle and samples the level.

Parameters

struct w1_master *dev: the master device

Description

Only call if dev->bus_master->touch_bit is NULL

The Linux Kernel

Contents

This Page

W1: Dallas’ 1-wire bus¶

W1 API internal to the kernel¶

include/linux/w1.h¶

drivers/w1/w1.c¶

drivers/w1/w1_family.c¶

drivers/w1/w1_internal.h¶

drivers/w1/w1_int.c¶

drivers/w1/w1_netlink.h¶

drivers/w1/w1_io.c¶