4. Remote Controller devices¶
4.1. Remote Controller core¶
The remote controller core implements infrastructure to receive and send remote controller keyboard keystrokes and mouse events.
Every time a key is pressed on a remote controller, a scan code is produced. Also, on most hardware, keeping a key pressed for more than a few dozens of milliseconds produce a repeat key event. That’s somewhat similar to what a normal keyboard or mouse is handled internally on Linux[1]. So, the remote controller core is implemented on the top of the linux input/evdev interface.
However, most of the remote controllers use infrared (IR) to transmit signals. As there are several protocols used to modulate infrared signals, one important part of the core is dedicated to adjust the driver and the core system to support the infrared protocol used by the emitter.
The infrared transmission is done by blinking a infrared emitter using a carrier. The carrier can be switched on or off by the IR transmitter hardware. When the carrier is switched on, it is called PULSE. When the carrier is switched off, it is called SPACE.
In other words, a typical IR transmission can be viewed as a sequence of PULSE and SPACE events, each with a given duration.
The carrier parameters (frequency, duty cycle) and the intervals for PULSE and SPACE events depend on the protocol. For example, the NEC protocol uses a carrier of 38kHz, and transmissions start with a 9ms PULSE and a 4.5ms SPACE. It then transmits 16 bits of scan code, being 8 bits for address (usually it is a fixed number for a given remote controller), followed by 8 bits of code. A bit “1” is modulated with 560µs PULSE followed by 1690µs SPACE and a bit “0” is modulated with 560µs PULSE followed by 560µs SPACE.
At receiver, a simple low-pass filter can be used to convert the received
signal in a sequence of PULSE/SPACE events, filtering out the carrier
frequency. Due to that, the receiver doesn’t care about the carrier’s
actual frequency parameters: all it has to do is to measure the amount
of time it receives PULSE/SPACE events.
So, a simple IR receiver hardware will just provide a sequence of timings
for those events to the Kernel. The drivers for hardware with such kind of
receivers are identified by  RC_DRIVER_IR_RAW, as defined by
rc_driver_type[2]. Other hardware come with a
microcontroller that decode the PULSE/SPACE sequence and return scan
codes to the Kernel. Such kind of receivers are identified
by RC_DRIVER_SCANCODE.
The RC core also supports devices that have just IR emitters,
without any receivers. Right now, all such devices work only in
raw TX mode. Such kind of hardware is identified as
RC_DRIVER_IR_RAW_TX.
When the RC core receives events produced by RC_DRIVER_IR_RAW IR
receivers, it needs to decode the IR protocol, in order to obtain the
corresponding scan code. The protocols supported by the RC core are
defined at enum rc_proto.
When the RC code receives a scan code (either directly, by a driver
of the type RC_DRIVER_SCANCODE, or via its IR decoders), it needs
to convert into a Linux input event code. This is done via a mapping
table.
The Kernel has support for mapping tables available on most media devices. It also supports loading a table in runtime, via some sysfs nodes. See the RC userspace API for more details.
4.1.1. Remote controller data structures and functions¶
- 
enum rc_driver_type¶
- type of the RC driver. 
Constants
- RC_DRIVER_SCANCODE
- Driver or hardware generates a scancode. 
- RC_DRIVER_IR_RAW
- Driver or hardware generates pulse/space sequences. It needs a Infra-Red pulse/space decoder 
- RC_DRIVER_IR_RAW_TX
- Device transmitter only, driver requires pulse/space data sequence. 
- 
struct rc_scancode_filter¶
- Filter scan codes. 
Definition:
struct rc_scancode_filter {
    u32 data;
    u32 mask;
};
Members
- data
- Scancode data to match. 
- mask
- Mask of bits of scancode to compare. 
- 
enum rc_filter_type¶
- Filter type constants. 
Constants
- RC_FILTER_NORMAL
- Filter for normal operation. 
- RC_FILTER_WAKEUP
- Filter for waking from suspend. 
- RC_FILTER_MAX
- Number of filter types. 
- 
struct lirc_fh¶
- represents an open lirc file 
Definition:
struct lirc_fh {
    struct list_head list;
    struct rc_dev *rc;
    int carrier_low;
    unsigned int *rawir;
    struct lirc_scancode *scancodes;
    wait_queue_head_t wait_poll;
    u8 send_mode;
    u8 rec_mode;
};
Members
- list
- list of open file handles 
- rc
- rcdev for this lirc chardev 
- carrier_low
- when setting the carrier range, first the low end must be set with an ioctl and then the high end with another ioctl 
- rawir
- queue for incoming raw IR 
- scancodes
- queue for incoming decoded scancodes 
- wait_poll
- poll struct for lirc device 
- send_mode
- lirc mode for sending, either LIRC_MODE_SCANCODE or LIRC_MODE_PULSE 
- rec_mode
- lirc mode for receiving, either LIRC_MODE_SCANCODE or LIRC_MODE_MODE2 
- 
struct rc_dev¶
- represents a remote control device 
Definition:
struct rc_dev {
    struct device                   dev;
    bool managed_alloc;
    const struct attribute_group    *sysfs_groups[5];
    const char                      *device_name;
    const char                      *input_phys;
    struct input_id                 input_id;
    const char                      *driver_name;
    const char                      *map_name;
    struct rc_map                   rc_map;
    struct mutex                    lock;
    unsigned int                    minor;
    struct ir_raw_event_ctrl        *raw;
    struct input_dev                *input_dev;
    enum rc_driver_type             driver_type;
    bool idle;
    bool encode_wakeup;
    u64 allowed_protocols;
    u64 enabled_protocols;
    u64 allowed_wakeup_protocols;
    enum rc_proto                   wakeup_protocol;
    struct rc_scancode_filter       scancode_filter;
    struct rc_scancode_filter       scancode_wakeup_filter;
    u32 scancode_mask;
    u32 users;
    void *priv;
    spinlock_t keylock;
    bool keypressed;
    unsigned long                   keyup_jiffies;
    struct timer_list               timer_keyup;
    struct timer_list               timer_repeat;
    u32 last_keycode;
    enum rc_proto                   last_protocol;
    u64 last_scancode;
    u8 last_toggle;
    u32 timeout;
    u32 min_timeout;
    u32 max_timeout;
    u32 rx_resolution;
#ifdef CONFIG_LIRC;
    struct device                   lirc_dev;
    struct cdev                     lirc_cdev;
    ktime_t gap_start;
    spinlock_t lirc_fh_lock;
    struct list_head                lirc_fh;
#endif;
    bool registered;
    int (*change_protocol)(struct rc_dev *dev, u64 *rc_proto);
    int (*open)(struct rc_dev *dev);
    void (*close)(struct rc_dev *dev);
    int (*s_tx_mask)(struct rc_dev *dev, u32 mask);
    int (*s_tx_carrier)(struct rc_dev *dev, u32 carrier);
    int (*s_tx_duty_cycle)(struct rc_dev *dev, u32 duty_cycle);
    int (*s_rx_carrier_range)(struct rc_dev *dev, u32 min, u32 max);
    int (*tx_ir)(struct rc_dev *dev, unsigned *txbuf, unsigned n);
    void (*s_idle)(struct rc_dev *dev, bool enable);
    int (*s_wideband_receiver)(struct rc_dev *dev, int enable);
    int (*s_carrier_report) (struct rc_dev *dev, int enable);
    int (*s_filter)(struct rc_dev *dev, struct rc_scancode_filter *filter);
    int (*s_wakeup_filter)(struct rc_dev *dev, struct rc_scancode_filter *filter);
    int (*s_timeout)(struct rc_dev *dev, unsigned int timeout);
};
Members
- dev
- driver model’s view of this device 
- managed_alloc
- devm_rc_allocate_device was used to create rc_dev 
- sysfs_groups
- sysfs attribute groups 
- device_name
- name of the rc child device 
- input_phys
- physical path to the input child device 
- input_id
- id of the input child device (struct input_id) 
- driver_name
- name of the hardware driver which registered this device 
- map_name
- name of the default keymap 
- rc_map
- current scan/key table 
- lock
- used to ensure we’ve filled in all protocol details before anyone can call show_protocols or store_protocols 
- minor
- unique minor remote control device number 
- raw
- additional data for raw pulse/space devices 
- input_dev
- the input child device used to communicate events to userspace 
- driver_type
- specifies if protocol decoding is done in hardware or software 
- idle
- used to keep track of RX state 
- encode_wakeup
- wakeup filtering uses IR encode API, therefore the allowed wakeup protocols is the set of all raw encoders 
- allowed_protocols
- bitmask with the supported RC_PROTO_BIT_* protocols 
- enabled_protocols
- bitmask with the enabled RC_PROTO_BIT_* protocols 
- allowed_wakeup_protocols
- bitmask with the supported RC_PROTO_BIT_* wakeup protocols 
- wakeup_protocol
- the enabled RC_PROTO_* wakeup protocol or RC_PROTO_UNKNOWN if disabled. 
- scancode_filter
- scancode filter 
- scancode_wakeup_filter
- scancode wakeup filters 
- scancode_mask
- some hardware decoders are not capable of providing the full scancode to the application. As this is a hardware limit, we can’t do anything with it. Yet, as the same keycode table can be used with other devices, a mask is provided to allow its usage. Drivers should generally leave this field in blank 
- users
- number of current users of the device 
- priv
- driver-specific data 
- keylock
- protects the remaining members of the struct 
- keypressed
- whether a key is currently pressed 
- keyup_jiffies
- time (in jiffies) when the current keypress should be released 
- timer_keyup
- timer for releasing a keypress 
- timer_repeat
- timer for autorepeat events. This is needed for CEC, which has non-standard repeats. 
- last_keycode
- keycode of last keypress 
- last_protocol
- protocol of last keypress 
- last_scancode
- scancode of last keypress 
- last_toggle
- toggle value of last command 
- timeout
- optional time after which device stops sending data 
- min_timeout
- minimum timeout supported by device 
- max_timeout
- maximum timeout supported by device 
- rx_resolution
- resolution (in us) of input sampler 
- lirc_dev
- lirc device 
- lirc_cdev
- lirc char cdev 
- gap_start
- start time for gap after timeout if non-zero 
- lirc_fh_lock
- protects lirc_fh list 
- lirc_fh
- list of open files 
- registered
- set to true by - rc_register_device(), false by rc_unregister_device
- change_protocol
- allow changing the protocol used on hardware decoders 
- open
- callback to allow drivers to enable polling/irq when IR input device is opened. 
- close
- callback to allow drivers to disable polling/irq when IR input device is opened. 
- s_tx_mask
- set transmitter mask (for devices with multiple tx outputs) 
- s_tx_carrier
- set transmit carrier frequency 
- s_tx_duty_cycle
- set transmit duty cycle (0% - 100%) 
- s_rx_carrier_range
- inform driver about carrier it is expected to handle 
- tx_ir
- transmit IR 
- s_idle
- enable/disable hardware idle mode, upon which, device doesn’t interrupt host until it sees IR pulses 
- s_wideband_receiver
- enable wide band receiver used for learning 
- s_carrier_report
- enable carrier reports 
- s_filter
- set the scancode filter 
- s_wakeup_filter
- set the wakeup scancode filter. If the mask is zero then wakeup should be disabled. wakeup_protocol will be set to a valid protocol if mask is nonzero. 
- s_timeout
- set hardware timeout in us 
- 
struct rc_dev *rc_allocate_device(enum rc_driver_type)¶
- Allocates a RC device 
Parameters
- enum rc_driver_type
- specifies the type of the RC output to be allocated returns a pointer to - struct rc_dev.
- 
struct rc_dev *devm_rc_allocate_device(struct device *dev, enum rc_driver_type)¶
- Managed RC device allocation 
Parameters
- struct device *dev
- pointer to - struct device
- enum rc_driver_type
- specifies the type of the RC output to be allocated returns a pointer to - struct rc_dev.
Parameters
- struct rc_dev *dev
- pointer to - struct rc_dev.
Parameters
- struct rc_dev *dev
- pointer to - struct rc_dev.
- 
int devm_rc_register_device(struct device *parent, struct rc_dev *dev)¶
- Manageded registering of a RC device 
Parameters
- struct device *parent
- pointer to - struct device.
- struct rc_dev *dev
- pointer to - struct rc_dev.
Parameters
- struct rc_dev *dev
- pointer to - struct rc_dev.
- 
struct rc_map_table¶
- represents a scancode/keycode pair 
Definition:
struct rc_map_table {
    u64 scancode;
    u32 keycode;
};
Members
- scancode
- scan code (u64) 
- keycode
- Linux input keycode 
- 
struct rc_map¶
- represents a keycode map table 
Definition:
struct rc_map {
    struct rc_map_table     *scan;
    unsigned int            size;
    unsigned int            len;
    unsigned int            alloc;
    enum rc_proto           rc_proto;
    const char              *name;
    spinlock_t lock;
};
Members
- scan
- pointer to struct - rc_map_table
- size
- Max number of entries 
- len
- Number of entries that are in use 
- alloc
- size of *scan, in bytes 
- rc_proto
- type of the remote controller protocol, as defined at enum - rc_proto
- name
- name of the key map table 
- lock
- lock to protect access to this structure 
Definition:
struct rc_map_list {
    struct list_head         list;
    struct rc_map map;
};
Members
- list
- pointer to struct - list_head
- map
- pointer to struct - rc_map
- 
int rc_map_register(struct rc_map_list *map)¶
- Registers a Remote Controller scancode map 
Parameters
- struct rc_map_list *map
- pointer to - struct rc_map_list
- 
void rc_map_unregister(struct rc_map_list *map)¶
- Unregisters a Remote Controller scancode map 
Parameters
- struct rc_map_list *map
- pointer to - struct rc_map_list
Parameters
- const char *name
- name of the RC scancode map