# W1: Dallas' 1-wire bus

David
Fries

                David@Fries.net

2013

This documentation is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License version 2.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. For more details see the file COPYING in the source distribution of Linux.

## W1 API internal to the kernel

### W1 API internal to the kernel

#### drivers/w1/w1.h

W1 core functions.

##### LINUX

Kernel Hackers Manual April 2018
struct w1_reg_num
9
4.4.0-121-

##### struct w1_reg_num

broken out slave device id

###### Synopsis

    struct w1_reg_num {
    #if defined(__LITTLE_ENDIAN_BITFIELD)
      __u64 family:8;
      __u64 id:48;
      __u64 crc:8;
    #elif defined(__BIG_ENDIAN_BITFIELD)
      __u64 crc:8;
      __u64 id:48;
      __u64 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

##### LINUX

Kernel Hackers Manual April 2018
struct w1_slave
9
4.4.0-121-

##### struct w1_slave

holds a single slave device on the bus

###### Synopsis

    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;
    };

###### Members

owner

  Points to the one wire wire kernel module.

name[W1_MAXNAMELEN]

  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

##### LINUX

Kernel Hackers Manual April 2018
struct w1_bus_master
9
4.4.0-121-

##### struct w1_bus_master

operations available on a bus master

###### Synopsis

    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);
    };

###### 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 bytes. 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 handles 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

###### 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.

##### LINUX

Kernel Hackers Manual April 2018
enum w1_master_flags
9
4.4.0-121-

##### enum w1_master_flags

bitfields used in w1_master.flags

###### Synopsis

    enum w1_master_flags {
      W1_ABORT_SEARCH,
      W1_WARN_MAX_COUNT
    };

###### Constants

W1_ABORT_SEARCH

  abort searching early on shutdown

W1_WARN_MAX_COUNT

  limit warning when the maximum count is reached

##### LINUX

Kernel Hackers Manual April 2018
struct w1_master
9
4.4.0-121-

##### struct w1_master

one per bus master

###### Synopsis

    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;
      int 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[W1_MAXNAMELEN]

  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

##### LINUX

Kernel Hackers Manual April 2018
struct w1_async_cmd
9
4.4.0-121-

##### struct w1_async_cmd

execute callback from the w1_process kthread

###### Synopsis

    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.c

W1 core functions.

##### LINUX

Kernel Hackers Manual April 2018
w1_search
9
4.4.0-121-

##### w1_search

Performs a ROM Search & registers any devices found.

###### Synopsis

       void w1_search
       struct w1_master * dev
       u8 search_type
       w1_slave_found_callback cb

###### Arguments

`dev`

  The master device to search

`search_type`

  W1_SEARCH to search all devices, or W1_ALARM_SEARCH to return only devices in the alarmed state

`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

##### LINUX

Kernel Hackers Manual April 2018
w1_process_callbacks
9
4.4.0-121-

##### w1_process_callbacks

execute each dev->async_list callback entry

###### Synopsis

       int w1_process_callbacks
       struct w1_master * dev

###### Arguments

`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.h

Allows registering device family operations.

##### LINUX

Kernel Hackers Manual April 2018
struct w1_family_ops
9
4.4.0-121-

##### struct w1_family_ops

operations for a family type

###### Synopsis

    struct w1_family_ops {
      int (* add_slave) (struct w1_slave *);
      void (* remove_slave) (struct w1_slave *);
      const struct attribute_group ** groups;
    };

###### Members

add_slave

  add_slave

remove_slave

  remove_slave

groups

  sysfs group

##### LINUX

Kernel Hackers Manual April 2018
struct w1_family
9
4.4.0-121-

##### struct w1_family

reference counted family structure.

###### Synopsis

    struct w1_family {
      struct list_head family_entry;
      u8 fid;
      struct w1_family_ops * fops;
      atomic_t refcnt;
    };

###### Members

family_entry

  family linked list

fid

  8 bit family identifier

fops

  operations for this family

refcnt

  reference counter

#### drivers/w1/w1_family.c

Allows registering device family operations.

##### LINUX

Kernel Hackers Manual April 2018
w1_register_family
9
4.4.0-121-

##### w1_register_family

register a device family driver

###### Synopsis

       int w1_register_family
       struct w1_family * newf

###### Arguments

`newf`

  family to register

##### LINUX

Kernel Hackers Manual April 2018
w1_unregister_family
9
4.4.0-121-

##### w1_unregister_family

unregister a device family driver

###### Synopsis

       void w1_unregister_family
       struct w1_family * fent

###### Arguments

`fent`

  family to unregister

#### drivers/w1/w1_int.c

W1 internal initialization for master devices.

##### LINUX

Kernel Hackers Manual April 2018
w1_add_master_device
9
4.4.0-121-

##### w1_add_master_device

registers a new master device

###### Synopsis

       int w1_add_master_device
       struct w1_bus_master * master

###### Arguments

`master`

  master bus device to register

##### LINUX

Kernel Hackers Manual April 2018
w1_remove_master_device
9
4.4.0-121-

##### w1_remove_master_device

unregister a master device

###### Synopsis

       void w1_remove_master_device
       struct w1_bus_master * bm

###### Arguments

`bm`

  master bus device to remove

#### drivers/w1/w1_netlink.h

W1 external netlink API structures and commands.

##### LINUX

Kernel Hackers Manual April 2018
enum w1_cn_msg_flags
9
4.4.0-121-

##### enum w1_cn_msg_flags

bitfield flags for struct cn_msg.flags

###### Synopsis

    enum w1_cn_msg_flags {
      W1_CN_BUNDLE
    };

###### 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.

##### LINUX

Kernel Hackers Manual April 2018
enum w1_netlink_message_types
9
4.4.0-121-

##### enum w1_netlink_message_types

message type

###### Synopsis

    enum w1_netlink_message_types {
      W1_SLAVE_ADD,
      W1_SLAVE_REMOVE,
      W1_MASTER_ADD,
      W1_MASTER_REMOVE,
      W1_MASTER_CMD,
      W1_SLAVE_CMD,
      W1_LIST_MASTERS
    };

###### 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

##### LINUX

Kernel Hackers Manual April 2018
struct w1_netlink_msg
9
4.4.0-121-

##### struct w1_netlink_msg

holds w1 message type, id, and result

###### Synopsis

    struct w1_netlink_msg {
      __u8 type;
      __u8 status;
      __u16 len;
      union id;
      __u8 data[0];
    };

###### 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 master bus id (msg.id) and slave device id (id[8]).

data[0]

  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).

##### LINUX

Kernel Hackers Manual April 2018
enum w1_commands
9
4.4.0-121-

##### enum w1_commands

commands available for master or slave operations

###### Synopsis

    enum w1_commands {
      W1_CMD_READ,
      W1_CMD_WRITE,
      W1_CMD_SEARCH,
      W1_CMD_ALARM_SEARCH,
      W1_CMD_TOUCH,
      W1_CMD_RESET,
      W1_CMD_SLAVE_ADD,
      W1_CMD_SLAVE_REMOVE,
      W1_CMD_LIST_SLAVES,
      W1_CMD_MAX
    };

###### 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

##### LINUX

Kernel Hackers Manual April 2018
struct w1_netlink_cmd
9
4.4.0-121-

##### struct w1_netlink_cmd

holds the command and data

###### Synopsis

    struct w1_netlink_cmd {
      __u8 cmd;
      __u8 res;
      __u16 len;
      __u8 data[0];
    };

###### Members

cmd

  one of enum w1_commands

res

  reserved

len

  length of data following w1_netlink_cmd

data[0]

  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.

##### LINUX

Kernel Hackers Manual April 2018
w1_write_8
9
4.4.0-121-

##### w1_write_8

Writes 8 bits.

###### Synopsis

       void w1_write_8
       struct w1_master * dev
       u8 byte

###### Arguments

`dev`

  the master device

`byte`

  the byte to write

##### LINUX

Kernel Hackers Manual April 2018
w1_read_8
9
4.4.0-121-

##### w1_read_8

Reads 8 bits.

###### Synopsis

       u8 w1_read_8
       struct w1_master * dev

###### Arguments

`dev`

  the master device

###### Return

the byte read

##### LINUX

Kernel Hackers Manual April 2018
w1_write_block
9
4.4.0-121-

##### w1_write_block

Writes a series of bytes.

###### Synopsis

       void w1_write_block
       struct w1_master * dev
       const u8 * buf
       int len

###### Arguments

`dev`

  the master device

`buf`

  pointer to the data to write

`len`

  the number of bytes to write

##### LINUX

Kernel Hackers Manual April 2018
w1_touch_block
9
4.4.0-121-

##### w1_touch_block

Touches a series of bytes.

###### Synopsis

       void w1_touch_block
       struct w1_master * dev
       u8 * buf
       int len

###### Arguments

`dev`

  the master device

`buf`

  pointer to the data to write

`len`

  the number of bytes to write

##### LINUX

Kernel Hackers Manual April 2018
w1_read_block
9
4.4.0-121-

##### w1_read_block

Reads a series of bytes.

###### Synopsis

       u8 w1_read_block
       struct w1_master * dev
       u8 * buf
       int len

###### Arguments

`dev`

  the master device

`buf`

  pointer to the buffer to fill

`len`

  the number of bytes to read

###### Return

the number of bytes read

##### LINUX

Kernel Hackers Manual April 2018
w1_reset_bus
9
4.4.0-121-

##### w1_reset_bus

Issues a reset bus sequence.

###### Synopsis

       int w1_reset_bus
       struct w1_master * dev

###### Arguments

`dev`

  the master device

###### Return

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

##### LINUX

Kernel Hackers Manual April 2018
w1_reset_select_slave
9
4.4.0-121-

##### w1_reset_select_slave

reset and select a slave

###### Synopsis

       int w1_reset_select_slave
       struct w1_slave * sl

###### Arguments

`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

##### LINUX

Kernel Hackers Manual April 2018
w1_reset_resume_command
9
4.4.0-121-

##### w1_reset_resume_command

resume instead of another match ROM

###### Synopsis

       int w1_reset_resume_command
       struct w1_master * dev

###### Arguments

`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.

##### LINUX

Kernel Hackers Manual April 2018
w1_next_pullup
9
4.4.0-121-

##### w1_next_pullup

register for a strong pullup

###### Synopsis

       void w1_next_pullup
       struct w1_master * dev
       int delay

###### Arguments

`dev`

  the master device

`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

##### LINUX

Kernel Hackers Manual April 2018
w1_touch_bit
9
4.4.0-121-

##### w1_touch_bit

Generates a write-0 or write-1 cycle and samples the level.

###### Synopsis

       u8 w1_touch_bit
       struct w1_master * dev
       int bit

###### Arguments

`dev`

  the master device

`bit`

  0 - write a 0, 1 - write a 0 read the level

##### LINUX

Kernel Hackers Manual April 2018
w1_write_bit
9
4.4.0-121-

##### w1_write_bit

Generates a write-0 or write-1 cycle.

###### Synopsis

       void w1_write_bit
       struct w1_master * dev
       int bit

###### Arguments

`dev`

  the master device

`bit`

  bit to write

###### Description

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

##### LINUX

Kernel Hackers Manual April 2018
w1_pre_write
9
4.4.0-121-

##### w1_pre_write

pre-write operations

###### Synopsis

       void w1_pre_write
       struct w1_master * dev

###### Arguments

`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.

##### LINUX

Kernel Hackers Manual April 2018
w1_post_write
9
4.4.0-121-

##### w1_post_write

post-write options

###### Synopsis

       void w1_post_write
       struct w1_master * dev

###### Arguments

`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.

##### LINUX

Kernel Hackers Manual April 2018
w1_read_bit
9
4.4.0-121-

##### w1_read_bit

Generates a write-1 cycle and samples the level.

###### Synopsis

       u8 w1_read_bit
       struct w1_master * dev

###### Arguments

`dev`

  the master device

###### Description

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

##### LINUX

Kernel Hackers Manual April 2018
w1_triplet
9
4.4.0-121-

##### w1_triplet

* Does a triplet - used for searching ROM addresses.

###### Synopsis

       u8 w1_triplet
       struct w1_master * dev
       int bdir

###### Arguments

`dev`

  the master device

`bdir`

  the bit to write if both id_bit and comp_bit are 0

###### 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