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+.. SPDX-License-Identifier: GPL-2.0 OR GFDL-1.1-no-invariants-or-later
+
+.. _Remote_controllers_Protocols:
+
+*****************************************
+Remote Controller Protocols and Scancodes
+*****************************************
+
+IR is encoded as a series of pulses and spaces, using a protocol. These
+protocols can encode e.g. an address (which device should respond) and a
+command: what it should do. The values for these are not always consistent
+across different devices for a given protocol.
+
+Therefore out the output of the IR decoder is a scancode; a single u32
+value. Using keymap tables this can be mapped to linux key codes.
+
+Other things can be encoded too. Some IR protocols encode a toggle bit; this
+is to distinguish whether the same button is being held down, or has been
+released and pressed again. If has been released and pressed again, the
+toggle bit will invert from one IR message to the next.
+
+Some remotes have a pointer-type device which can used to control the
+mouse; some air conditioning systems can have their target temperature
+target set in IR.
+
+The following are the protocols the kernel knows about and also lists
+how scancodes are encoded for each protocol.
+
+rc-5 (RC_PROTO_RC5)
+-------------------
+
+This IR protocol uses manchester encoding to encode 14 bits. There is a
+detailed description here https://www.sbprojects.net/knowledge/ir/rc5.php.
+
+The scancode encoding is *not* consistent with the lirc daemon (lircd) rc5
+protocol, or the manchester BPF decoder.
+
+.. flat-table:: rc5 bits scancode mapping
+ :widths: 1 1 2
+
+ * - rc-5 bit
+
+ - scancode bit
+
+ - description
+
+ * - 1
+
+ - none
+
+ - Start bit, always set
+
+ * - 1
+
+ - 6 (inverted)
+
+ - 2nd start bit in rc5, re-used as 6th command bit
+
+ * - 1
+
+ - none
+
+ - Toggle bit
+
+ * - 5
+
+ - 8 to 13
+
+ - Address
+
+ * - 6
+
+ - 0 to 5
+
+ - Command
+
+There is a variant of rc5 called either rc5x or extended rc5
+where there the second stop bit is the 6th commmand bit, but inverted.
+This is done so it the scancodes and encoding is compatible with existing
+schemes. This bit is stored in bit 6 of the scancode, inverted. This is
+done to keep it compatible with plain rc-5 where there are two start bits.
+
+rc-5-sz (RC_PROTO_RC5_SZ)
+-------------------------
+This is much like rc-5 but one bit longer. The scancode is encoded
+differently.
+
+.. flat-table:: rc-5-sz bits scancode mapping
+ :widths: 1 1 2
+
+ * - rc-5-sz bits
+
+ - scancode bit
+
+ - description
+
+ * - 1
+
+ - none
+
+ - Start bit, always set
+
+ * - 1
+
+ - 13
+
+ - Address bit
+
+ * - 1
+
+ - none
+
+ - Toggle bit
+
+ * - 6
+
+ - 6 to 11
+
+ - Address
+
+ * - 6
+
+ - 0 to 5
+
+ - Command
+
+rc-5x-20 (RC_PROTO_RC5X_20)
+---------------------------
+
+This rc-5 extended to encoded 20 bits. The is a 3555 microseconds space
+after the 8th bit.
+
+.. flat-table:: rc-5x-20 bits scancode mapping
+ :widths: 1 1 2
+
+ * - rc-5-sz bits
+
+ - scancode bit
+
+ - description
+
+ * - 1
+
+ - none
+
+ - Start bit, always set
+
+ * - 1
+
+ - 14
+
+ - Address bit
+
+ * - 1
+
+ - none
+
+ - Toggle bit
+
+ * - 5
+
+ - 16 to 20
+
+ - Address
+
+ * - 6
+
+ - 8 to 13
+
+ - Address
+
+ * - 6
+
+ - 0 to 5
+
+ - Command
+
+
+jvc (RC_PROTO_JVC)
+------------------
+
+The jvc protocol is much like nec, without the inverted values. It is
+described here https://www.sbprojects.net/knowledge/ir/jvc.php.
+
+The scancode is a 16 bits value, where the address is the lower 8 bits
+and the command the higher 8 bits; this is reversed from IR order.
+
+sony-12 (RC_PROTO_SONY12)
+-------------------------
+
+The sony protocol is a pulse-width encoding. There are three variants,
+which just differ in number of bits and scancode encoding.
+
+.. flat-table:: sony-12 bits scancode mapping
+ :widths: 1 1 2
+
+ * - sony-12 bits
+
+ - scancode bit
+
+ - description
+
+ * - 5
+
+ - 16 to 20
+
+ - device
+
+ * - 7
+
+ - 0 to 6
+
+ - function
+
+sony-15 (RC_PROTO_SONY15)
+-------------------------
+
+The sony protocol is a pulse-width encoding. There are three variants,
+which just differ in number of bits and scancode encoding.
+
+.. flat-table:: sony-12 bits scancode mapping
+ :widths: 1 1 2
+
+ * - sony-12 bits
+
+ - scancode bit
+
+ - description
+
+ * - 8
+
+ - 16 to 23
+
+ - device
+
+ * - 7
+
+ - 0 to 6
+
+ - function
+
+sony-20 (RC_PROTO_SONY20)
+-------------------------
+
+The sony protocol is a pulse-width encoding. There are three variants,
+which just differ in number of bits and scancode encoding.
+
+.. flat-table:: sony-20 bits scancode mapping
+ :widths: 1 1 2
+
+ * - sony-20 bits
+
+ - scancode bit
+
+ - description
+
+ * - 5
+
+ - 16 to 20
+
+ - device
+
+ * - 7
+
+ - 0 to 7
+
+ - device
+
+ * - 8
+
+ - 8 to 15
+
+ - extended bits
+
+nec (RC_PROTO_NEC)
+------------------
+
+The nec protocol encodes an 8 bit address and an 8 bit command. It is
+described here https://www.sbprojects.net/knowledge/ir/nec.php. Note
+that the protocol sends least significant bit first.
+
+As a check, the nec protocol sends the address and command twice; the
+second time it is inverted. This is done for verification.
+
+A plain nec IR message has 16 bits; the high 8 bits are the address
+and the low 8 bits are the command.
+
+nec-x (RC_PROTO_NECX)
+---------------------
+
+Extended nec has a 16 bit address and a 8 bit command. This is encoded
+as a 24 bit value as you would expect, with the lower 8 bits the command
+and the upper 16 bits the address.
+
+nec-32 (RC_PROTO_NEC32)
+-----------------------
+
+nec-32 does not send an inverted address or an inverted command; the
+entire message, all 32 bits, are used.
+
+For this to be decoded correctly, the second 8 bits must not be the
+inverted value of the first, and also the last 8 bits must not be the
+inverted value of the third 8 bit value.
+
+The scancode has a somewhat unusual encoding.
+
+.. flat-table:: nec-32 bits scancode mapping
+
+ * - nec-32 bits
+
+ - scancode bit
+
+ * - First 8 bits
+
+ - 16 to 23
+
+ * - Second 8 bits
+
+ - 24 to 31
+
+ * - Third 8 bits
+
+ - 0 to 7
+
+ * - Fourth 8 bits
+
+ - 8 to 15
+
+sanyo (RC_PROTO_SANYO)
+----------------------
+
+The sanyo protocol is like the nec protocol, but with 13 bits address
+rather than 8 bits. Both the address and the command are followed by
+their inverted versions, but these are not present in the scancodes.
+
+Bis 8 to 20 of the scancode is the 13 bits address, and the lower 8
+bits are the command.
+
+mcir2-kbd (RC_PROTO_MCIR2_KBD)
+------------------------------
+
+This protocol is generated by the Microsoft MCE keyboard for keyboard
+events. Refer to the ir-mce_kbd-decoder.c to see how it is encoded.
+
+mcir2-mse (RC_PROTO_MCIR2_MSE)
+------------------------------
+
+This protocol is generated by the Microsoft MCE keyboard for pointer
+events. Refer to the ir-mce_kbd-decoder.c to see how it is encoded.
+
+rc-6-0 (RC_PROTO_RC6_0)
+-----------------------
+
+This is the rc-6 in mode 0. rc-6 is described here
+https://www.sbprojects.net/knowledge/ir/rc6.php.
+The scancode is the exact 16 bits as in the protocol. There is also a
+toggle bit.
+
+rc-6-6a-20 (RC_PROTO_RC6_6A_20)
+-------------------------------
+
+This is the rc-6 in mode 6a, 20 bits. rc-6 is described here
+https://www.sbprojects.net/knowledge/ir/rc6.php.
+The scancode is the exact 20 bits
+as in the protocol. There is also a toggle bit.
+
+rc-6-6a-24 (RC_PROTO_RC6_6A_24)
+-------------------------------
+
+This is the rc-6 in mode 6a, 24 bits. rc-6 is described here
+https://www.sbprojects.net/knowledge/ir/rc6.php.
+The scancode is the exact 24 bits
+as in the protocol. There is also a toggle bit.
+
+rc-6-6a-32 (RC_PROTO_RC6_6A_32)
+-------------------------------
+
+This is the rc-6 in mode 6a, 32 bits. rc-6 is described here
+https://www.sbprojects.net/knowledge/ir/rc6.php.
+The upper 16 bits are the vendor,
+and the lower 16 bits are the vendor-specific bits. This protocol is
+for the non-Microsoft MCE variant (vendor != 0x800f).
+
+
+rc-6-mce (RC_PROTO_RC6_MCE)
+---------------------------
+
+This is the rc-6 in mode 6a, 32 bits. The upper 16 bits are the vendor,
+and the lower 16 bits are the vendor-specific bits. This protocol is
+for the Microsoft MCE variant (vendor = 0x800f). The toggle bit in the
+protocol itself is ignored, and the 16th bit should be takes as the toggle
+bit.
+
+sharp (RC_PROTO_SHARP)
+----------------------
+
+This is a protocol used by Sharp VCRs, is described here
+https://www.sbprojects.net/knowledge/ir/sharp.php. There is a very long
+(40ms) space between the normal and inverted values, and some IR receivers
+cannot decode this.
+
+There is a 5 bit address and a 8 bit command. In the scancode the address is
+in bits 8 to 12, and the command in bits 0 to 7.
+
+xmp (RC_PROTO_XMP)
+------------------
+
+This protocol has several versions and only version 1 is supported. Refer
+to the decoder (ir-xmp-decoder.c) to see how it is encoded.
+
+
+cec (RC_PROTO_CEC)
+------------------
+
+This is not an IR protocol, this is a protocol over CEC. The CEC
+infrastructure uses rc-core for handling CEC commands, so that they
+can easily be remapped.
+
+imon (RC_PROTO_IMON)
+--------------------
+
+This protocol is used by Antec Veris/SoundGraph iMON remotes.
+
+The protocol
+describes both button presses and pointer movements. The protocol encodes
+31 bits, and the scancode is simply the 31 bits with the top bit always 0.
+
+rc-mm-12 (RC_PROTO_RCMM12)
+--------------------------
+
+The rc-mm protocol is described here
+https://www.sbprojects.net/knowledge/ir/rcmm.php. The scancode is simply
+the 12 bits.
+
+rc-mm-24 (RC_PROTO_RCMM24)
+--------------------------
+
+The rc-mm protocol is described here
+https://www.sbprojects.net/knowledge/ir/rcmm.php. The scancode is simply
+the 24 bits.
+
+rc-mm-32 (RC_PROTO_RCMM32)
+--------------------------
+
+The rc-mm protocol is described here
+https://www.sbprojects.net/knowledge/ir/rcmm.php. The scancode is simply
+the 32 bits.
+
+xbox-dvd (RC_PROTO_XBOX_DVD)
+----------------------------
+
+This protocol is used by XBox DVD Remote, which was made for the original
+XBox. There is no in-kernel decoder or encoder for this protocol. The usb
+device decodes the protocol. There is a BPF decoder available in v4l-utils.