summaryrefslogtreecommitdiff
path: root/Documentation/w1/w1.generic
diff options
context:
space:
mode:
Diffstat (limited to 'Documentation/w1/w1.generic')
-rw-r--r--Documentation/w1/w1.generic113
1 files changed, 113 insertions, 0 deletions
diff --git a/Documentation/w1/w1.generic b/Documentation/w1/w1.generic
new file mode 100644
index 000000000..b2033c64c
--- /dev/null
+++ b/Documentation/w1/w1.generic
@@ -0,0 +1,113 @@
+The 1-wire (w1) subsystem
+------------------------------------------------------------------
+The 1-wire bus is a simple master-slave bus that communicates via a single
+signal wire (plus ground, so two wires).
+
+Devices communicate on the bus by pulling the signal to ground via an open
+drain output and by sampling the logic level of the signal line.
+
+The w1 subsystem provides the framework for managing w1 masters and
+communication with slaves.
+
+All w1 slave devices must be connected to a w1 bus master device.
+
+Example w1 master devices:
+ DS9490 usb device
+ W1-over-GPIO
+ DS2482 (i2c to w1 bridge)
+ Emulated devices, such as a RS232 converter, parallel port adapter, etc
+
+
+What does the w1 subsystem do?
+------------------------------------------------------------------
+When a w1 master driver registers with the w1 subsystem, the following occurs:
+
+ - sysfs entries for that w1 master are created
+ - the w1 bus is periodically searched for new slave devices
+
+When a device is found on the bus, w1 core tries to load the driver for its family
+and check if it is loaded. If so, the family driver is attached to the slave.
+If there is no driver for the family, default one is assigned, which allows to perform
+almost any kind of operations. Each logical operation is a transaction
+in nature, which can contain several (two or one) low-level operations.
+Let's see how one can read EEPROM context:
+1. one must write control buffer, i.e. buffer containing command byte
+and two byte address. At this step bus is reset and appropriate device
+is selected using either W1_SKIP_ROM or W1_MATCH_ROM command.
+Then provided control buffer is being written to the wire.
+2. reading. This will issue reading eeprom response.
+
+It is possible that between 1. and 2. w1 master thread will reset bus for searching
+and slave device will be even removed, but in this case 0xff will
+be read, since no device was selected.
+
+
+W1 device families
+------------------------------------------------------------------
+Slave devices are handled by a driver written for a family of w1 devices.
+
+A family driver populates a struct w1_family_ops (see w1_family.h) and
+registers with the w1 subsystem.
+
+Current family drivers:
+w1_therm - (ds18?20 thermal sensor family driver)
+ provides temperature reading function which is bound to ->rbin() method
+ of the above w1_family_ops structure.
+
+w1_smem - driver for simple 64bit memory cell provides ID reading method.
+
+You can call above methods by reading appropriate sysfs files.
+
+
+What does a w1 master driver need to implement?
+------------------------------------------------------------------
+
+The driver for w1 bus master must provide at minimum two functions.
+
+Emulated devices must provide the ability to set the output signal level
+(write_bit) and sample the signal level (read_bit).
+
+Devices that support the 1-wire natively must provide the ability to write and
+sample a bit (touch_bit) and reset the bus (reset_bus).
+
+Most hardware provides higher-level functions that offload w1 handling.
+See struct w1_bus_master definition in w1.h for details.
+
+
+w1 master sysfs interface
+------------------------------------------------------------------
+<xx-xxxxxxxxxxxxx> - a directory for a found device. The format is family-serial
+bus - (standard) symlink to the w1 bus
+driver - (standard) symlink to the w1 driver
+w1_master_add - Manually register a slave device
+w1_master_attempts - the number of times a search was attempted
+w1_master_max_slave_count
+ - maximum number of slaves to search for at a time
+w1_master_name - the name of the device (w1_bus_masterX)
+w1_master_pullup - 5V strong pullup 0 enabled, 1 disabled
+w1_master_remove - Manually remove a slave device
+w1_master_search - the number of searches left to do, -1=continual (default)
+w1_master_slave_count
+ - the number of slaves found
+w1_master_slaves - the names of the slaves, one per line
+w1_master_timeout - the delay in seconds between searches
+
+If you have a w1 bus that never changes (you don't add or remove devices),
+you can set the module parameter search_count to a small positive number
+for an initially small number of bus searches. Alternatively it could be
+set to zero, then manually add the slave device serial numbers by
+w1_master_add device file. The w1_master_add and w1_master_remove files
+generally only make sense when searching is disabled, as a search will
+redetect manually removed devices that are present and timeout manually
+added devices that aren't on the bus.
+
+
+w1 slave sysfs interface
+------------------------------------------------------------------
+bus - (standard) symlink to the w1 bus
+driver - (standard) symlink to the w1 driver
+name - the device name, usually the same as the directory name
+w1_slave - (optional) a binary file whose meaning depends on the
+ family driver
+rw - (optional) created for slave devices which do not have
+ appropriate family driver. Allows to read/write binary data.