diff --git a/Documentation/DocBook/v4l/lirc_device_interface.xml b/Documentation/DocBook/v4l/lirc_device_interface.xml new file mode 100644 index 000000000000..d9ae6803c2fc --- /dev/null +++ b/Documentation/DocBook/v4l/lirc_device_interface.xml @@ -0,0 +1,235 @@ +LIRC Device Interface + + +
+Introduction + +The LIRC device interface is a bi-directional interface for +transporting raw IR data between userspace and kernelspace. Fundamentally, +it is just a chardev (/dev/lircX, for X = 0, 1, 2, ...), with a number +of standard struct file_operations defined on it. With respect to +transporting raw IR data to and fro, the essential fops are read, write +and ioctl. + +Example dmesg output upon a driver registering w/LIRC: +
+ $ dmesg |grep lirc_dev + lirc_dev: IR Remote Control driver registered, major 248 + rc rc0: lirc_dev: driver ir-lirc-codec (mceusb) registered at minor = 0 +
+ + +What you should see for a chardev: +
+ $ ls -l /dev/lirc* + crw-rw---- 1 root root 248, 0 Jul 2 22:20 /dev/lirc0 +
+ + + +
+LIRC read fop + +The lircd userspace daemon reads raw IR data from the LIRC chardev. The +exact format of the data depends on what modes a driver supports, and what +mode has been selected. lircd obtains supported modes and sets the active mode +via the ioctl interface, detailed at . The generally +preferred mode is LIRC_MODE_MODE2, in which packets containing an int value +describing an IR signal are read from the chardev. + +See also http://www.lirc.org/html/technical.html for more info. + + +
+LIRC write fop + +The data written to the chardev is a pulse/space sequence of integer +values. Pulses and spaces are only marked implicitly by their position. The +data must start and end with a pulse, therefore, the data must always include +an unevent number of samples. The write function must block until the data has +been transmitted by the hardware. + + +
+ LIRC ioctl fop + +The LIRC device's ioctl definition is bound by the ioctl function +definition of struct file_operations, leaving us with an unsigned int +for the ioctl command and an unsigned long for the arg. For the purposes +of ioctl portability across 32-bit and 64-bit, these values are capped +to their 32-bit sizes. + +The following ioctls can be used to change specific hardware settings. +In general each driver should have a default set of settings. The driver +implementation is expected to re-apply the default settings when the device +is closed by user-space, so that every application opening the device can rely +on working with the default settings initially. + + + + LIRC_GET_FEATURES + + Obviously, get the underlying hardware device's features. If a driver + does not announce support of certain features, calling of the corresponding + ioctls is undefined. + + + + LIRC_GET_SEND_MODE + + Get supported transmit mode. Only LIRC_MODE_PULSE is supported by lircd. + + + + LIRC_GET_REC_MODE + + Get supported receive modes. Only LIRC_MODE_MODE2 and LIRC_MODE_LIRCCODE + are supported by lircd. + + + + LIRC_GET_SEND_CARRIER + + Get carrier frequency (in Hz) currently used for transmit. + + + + LIRC_GET_REC_CARRIER + + Get carrier frequency (in Hz) currently used for IR reception. + + + + LIRC_{G,S}ET_{SEND,REC}_DUTY_CYCLE + + Get/set the duty cycle (from 0 to 100) of the carrier signal. Currently, + no special meaning is defined for 0 or 100, but this could be used to switch + off carrier generation in the future, so these values should be reserved. + + + + LIRC_GET_REC_RESOLUTION + + Some receiver have maximum resolution which is defined by internal + sample rate or data format limitations. E.g. it's common that signals can + only be reported in 50 microsecond steps. This integer value is used by + lircd to automatically adjust the aeps tolerance value in the lircd + config file. + + + + LIRC_GET_M{IN,AX}_TIMEOUT + + Some devices have internal timers that can be used to detect when + there's no IR activity for a long time. This can help lircd in detecting + that a IR signal is finished and can speed up the decoding process. + Returns an integer value with the minimum/maximum timeout that can be + set. Some devices have a fixed timeout, in that case both ioctls will + return the same value even though the timeout cannot be changed. + + + + LIRC_GET_M{IN,AX}_FILTER_{PULSE,SPACE} + + Some devices are able to filter out spikes in the incoming signal + using given filter rules. These ioctls return the hardware capabilities + that describe the bounds of the possible filters. Filter settings depend + on the IR protocols that are expected. lircd derives the settings from + all protocols definitions found in its config file. + + + + LIRC_GET_LENGTH + + Retrieves the code length in bits (only for LIRC_MODE_LIRCCODE). + Reads on the device must be done in blocks matching the bit count. + The bit could should be rounded up so that it matches full bytes. + + + + LIRC_SET_{SEND,REC}_MODE + + Set send/receive mode. Largely obsolete for send, as only + LIRC_MODE_PULSE is supported. + + + + LIRC_SET_{SEND,REC}_CARRIER + + Set send/receive carrier (in Hz). + + + + LIRC_SET_TRANSMITTER_MASK + + This enables the given set of transmitters. The first transmitter + is encoded by the least significant bit, etc. When an invalid bit mask + is given, i.e. a bit is set, even though the device does not have so many + transitters, then this ioctl returns the number of available transitters + and does nothing otherwise. + + + + LIRC_SET_REC_TIMEOUT + + Sets the integer value for IR inactivity timeout (cf. + LIRC_GET_MIN_TIMEOUT and LIRC_GET_MAX_TIMEOUT). A value of 0 (if + supported by the hardware) disables all hardware timeouts and data should + be reported as soon as possible. If the exact value cannot be set, then + the next possible value _greater_ than the given value should be set. + + + + LIRC_SET_REC_TIMEOUT_REPORTS + + Enable (1) or disable (0) timeout reports in LIRC_MODE_MODE2. By + default, timeout reports should be turned off. + + + + LIRC_SET_REC_FILTER_{,PULSE,SPACE} + + Pulses/spaces shorter than this are filtered out by hardware. If + filters cannot be set independently for pulse/space, the corresponding + ioctls must return an error and LIRC_SET_REC_FILTER shall be used instead. + + + + LIRC_SET_MEASURE_CARRIER_MODE + + Enable (1)/disable (0) measure mode. If enabled, from the next key + press on, the driver will send LIRC_MODE2_FREQUENCY packets. By default + this should be turned off. + + + + LIRC_SET_REC_{DUTY_CYCLE,CARRIER}_RANGE + + To set a range use LIRC_SET_REC_DUTY_CYCLE_RANGE/LIRC_SET_REC_CARRIER_RANGE + with the lower bound first and later LIRC_SET_REC_DUTY_CYCLE/LIRC_SET_REC_CARRIER + with the upper bound. + + + + LIRC_NOTIFY_DECODE + + This ioctl is called by lircd whenever a successful decoding of an + incoming IR signal could be done. This can be used by supporting hardware + to give visual feedback to the user e.g. by flashing a LED. + + + + LIRC_SETUP_{START,END} + + Setting of several driver parameters can be optimized by encapsulating + the according ioctl calls with LIRC_SETUP_START/LIRC_SETUP_END. When a + driver receives a LIRC_SETUP_START ioctl it can choose to not commit + further setting changes to the hardware until a LIRC_SETUP_END is received. + But this is open to the driver implementation and every driver must also + handle parameter changes which are not encapsulated by LIRC_SETUP_START + and LIRC_SETUP_END. Drivers can also choose to ignore these ioctls. + + + + +