W1: Dallas’ 1-wire bus¶
| Author: | David Fries |
|---|
W1 API internal to the kernel¶
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;
__u64 id:48;
__u64 crc:8;
#elif defined(__BIG_ENDIAN_BITFIELD
__u64 crc:8;
__u64 id:48;
__u64 family:8;
#else
#error "Please fix \\\lt;asm/byteorder.h\\\gt;"
#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;
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);
};
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.
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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
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struct
w1_master¶ one per bus master
Definition
struct w1_master {
struct list_head w1_master_entry;
struct module * owner;
unsigned char name;
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- 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;
atomic_t refcnt;
};
Members
family_entry- family linked list
fid- 8 bit family identifier
fops- operations for this family
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
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_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 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 master bus id (msg.id) and slave device id (id[8]).
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.
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
-
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
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