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 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
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;
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 ( __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[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 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[0];
};
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