IR User Guide¶

REVISION HISTORY¶

Revision No.	Description	Date
1.0	Initial release	12/25/2023
1.1	Add Chapter VIII DEBUG&FAQ	11/27/2025

1. Overview¶

Infrared Receiver (IR) is mainly used to analyze the signal sent by the infrared remote control, which is a series of binary pulse codes. In order to prevent the infrared signal from being interfered by other signals during wireless transmission, it is usually modulated at a specific carrier frequency (38KHZ) and then transmitted through the infrared transmitting diode. The IR receives the signal of the specific frequency after filtering out other clutter and restores it to a binary pulse code, that is, demodulation. The decoding methods supported by Sgs IR are Full, Raw, SW and RC, and the protocols supported are NEC, RC5 and RC6.

2. Keyword¶

None.

3. FUNCTION DESCRIPTION¶

3.1. Basic Function¶

Support 5 groups of IR hardware.
Pulse signals less than 170us will be filtered.
The default clock frequency is 12MHZ, and the clock adjustment is not supported.
Supported decoding modes are Full, Raw, SW and RC5 (note that RC6 software is not supported yet), for configuration details, see IR DTS Configuration Description.

3.2. IR Decoding Method¶

Sgs's IR_IN signal can be decoded in four decoding modes: Full mode, Raw mode, SW mode, and RC mode.

If the IR_IN is in NEC/NEC-like format, you can use Full/Raw/SW mode to decode.

If the IR_IN is in RC format, you can use RC/SW mode to decode. (Note that, currently, only RC5 is supported by the driver.)

And if the format of the IR_IN is none of the above, you can only use SW mode (together with a decoder) to decode.

Full mode

Hardware can decode IR_IN signal in NEC/NEC-like format, and distinguish customer code from key code.
Raw mode

Hardware can decode IR_IN signal in NEC/NEC-like format, but cannot distinguish customer code from key code. This can only be determined by software.
SW mode

Hardware cannot identify any format from the IR_IN signal. Software decoding sigmal format, customer code and key code are required.
RC mode

Hardware can decode IR_IN signal in RC format, and distinguish customer code from key code.

As shown in the figure below, IR decode contains two main paths. The upper path is for Full/Raw/SW mode, while the lower path is for RC mode.

Figure 2-1: IR Decode Block Diagram

3.3. Each Protocol Level Standard¶

NEC format:

Logic0: 0.56ms high + 0.56ms low
Logic1: 0.56ms high + 1.68ms low
Header code: 9ms high pulse
Off code: 4.5ms low pulse
Customer code: 8-bit customer code + 8-bit inverse or 16-bit customer code
Command code: 8-bit command code + 8-bit inverse
Total cycle time: 108ms
Repeat key: 9ms Header code and 2.5ms Off code

Figure 2-2: NEC Format Standard

NEC-like format:

Logic0: short high + short low (usually 1:1)
Logic1: short high + long low (usually 1:3)
Header code: ultra long high width
Off code: ultra long low width

RC5 format:

Logic0: 888us high + 888us low (Manchester code)
Logic1: 888us low + 888us high (Manchester code)
Start bits: 2-bit logic1
Toggle bit: Inverted every time when the key is released and pressed again
Customer code: 5-bit customer code
Command code: 6-bit command code
Total cycle time: 114ms
If a key is held over 114ms, it will repeat the signal every cycle time

Figure 2-3: RC5 Format Standard

RC5-Extended format:

Same as RC5, only the second bit of SB is represented as the 6^th bit of the address code.

Figure 2-4: RC5-Extended Format Standard

RC6 mode 0 format:

Logic0: 444us low + 444us high (Manchester code)
Logic1: 444us high + 444us low (Manchester code)

(Note the logic length is half of RC5 format and the level order is opposite)
Header code: 2.666ms high pulse + 888us low pulse
Start bit: 1-bit logic1
Mode bits: 3-bit logic0 (in mode 0)
Toggle bit: Inverted every time when the key is released and pressed again
Customer code: 8-bit customer code
Command code: 8-bit key code
If a key is held over 114ms, it will repeat the signal every cycle time.

Figure 2-5: RC6 Mode 0 Format Standard

4. HARDWARE CONNECTION INTRODUCTION¶

Connect the infrared receiver to the development board according to the direction indicated in the schematic.

Figure 4-1: IR Hardware Schematic

5. Uboot USAGE INTRODUCTION¶

Not Support.

6. KERNEL USAGE INTRODUCTION¶

Driver path: kernel/drivers/sstar/ir

6.1. Configure Kernel Config¶

The configurations required for configuring kernel are set forth below.

If SW mode is not used, only the following two config options are required:

Device Driver->

    <*> SStar SoC platform drivers->

        <*> Sstar IR driver

Device Driver->

    Input device support->

        <*> Generic input layer(needed for keyboard, mouse….)

If SW mode is used, a decoder is required. You can use the decoder in Kernel to decode. Let's take NEC protocol as an example:

Device Driver->

    <*> Remote Controller support->

        <*> Remote Controller decoders->

            <*> Enable IR raw decoder for the NEC protocol

6.2. Configure DTS¶

To configure the IR DTS, you need only configure the following information in the corresponding chipname.dtsi.

ir: ir@1F007A00 {
    compatible = "sstar,ir";
    reg = <0x1F007A00 0x200>;
    clocks = <&CLK_ir>;
    interrupts = <GIC_SPI INT_FIQ_IR IRQ_TYPE_LEVEL_HIGH>,<GIC_SPI INT_FIQ_IR_RC IRQ_TYPE_LEVEL_HIGH>;
    group = <0>;
    /*
     * decode mode selection
     * FULL   1  Format: NEC/NECX
     * RAW    2  Format: NEC/NECX
     * RC5    3  Format: RC5
     * SW     4  Format: /
     */
    mode = <2>;
    //choose enum rc_proto for sw mode
    protocol = <9>;
    vendor = <0x000E>;
    product = <0x3412>;
    //rc-map-table = <customer_code + command_code  input_key_code>
    rc-map-table =
        //NEC Remote Control NO.1
        <0x00FFA8 KEY_POWER>,          <0x00FFC0 KEY_F5>,            <0x00FFDD KEY_GREEN>,
        <0x00FF44 KEY_F19>,            <0x00FFCA KEY_UP>,            <0x00FFD2 KEY_DOWN>,
        <0x00FF99 KEY_LEFT>,           <0x00FFC1 KEY_RIGHT>,         <0x00FFCE KEY_ENTER>,
        <0x00FFCB KEY_BACK>,           <0x00FF87 KEY_HOMEPAGE>,      <0x00FF97 KEY_COMPOSE>,
        <0x00FF41 KEY_PLAYPAUSE>,      <0x00FF0F KEY_F16>,           <0x00FF60 KEY_F20>,
        <0x00FF90 KEY_VOLUMEUP>,       <0x00FF98 KEY_VOLUMEDOWN>,    <0x00FFD1 KEY_MUTE>,
        //NEC Remote Control NO.2
        <0x807F46  KEY_POWER>,          <0x807F50  KEY_0>,           <0x807F49  KEY_1>,
        <0x807F55  KEY_2>,              <0x807F59  KEY_3>,           <0x807F4D  KEY_4>,
        <0x807F51  KEY_5>,              <0x807F5D  KEY_6>,           <0x807F48  KEY_7>,
        <0x807F54  KEY_8>,              <0x807F58  KEY_9>,           <0x807F47  KEY_RED>,
        <0x807F4B  KEY_GREEN>,          <0x807F57  KEY_YELLOW>,      <0x807F5B  KEY_BLUE>,
        <0x807F52  KEY_UP>,             <0x807F13  KEY_DOWN>,        <0x807F06  KEY_LEFT>,
        <0x807F1A  KEY_RIGHT>,          <0x807F0F  KEY_ENTER>,       <0x807F1F  KEY_CHANNELUP>,
        <0x807F19  KEY_CHANNELDOWN>,    <0x807F16  KEY_VOLUMEUP>,    <0x807F15  KEY_VOLUMEDOWN>,
        <0x807F03  KEY_PAGEUP>,         <0x807F05  KEY_PAGEDOWN>,    <0x807F17  KEY_HOME>,
        <0x807F07  KEY_MENU>,           <0x807F1B  KEY_BACK>,        <0x807F5A  KEY_MUTE>,
        <0x807F0D  KEY_RECORD>,         <0x807F42  KEY_HELP>,        <0x807F14  KEY_INFO>,
        <0x807F40  KEY_KP0>,            <0x807F04  KEY_KP1>,         <0x807F0E  KEY_REWIND>,
        <0x807F12  KEY_FORWARD>,        <0x807F4C  KEY_ZOOM>,        <0x807F02  KEY_PREVIOUSSONG>,
        <0x807F1E  KEY_NEXTSONG>,       <0x807F01  KEY_PLAY>,        <0x807F1D  KEY_PAUSE>,
        <0x807F11  KEY_STOP>,           <0x807F44  KEY_AUDIO>,       <0x807F56  KEY_CAMERA>,
        <0x807F5C  KEY_CHANNEL>,        <0x807F45  KEY_SLEEP>,       <0x807F4A  KEY_EPG>,
        <0x807F10  KEY_LIST>,           <0x807F53  KEY_SUBTITLE>,    <0x807F41  KEY_FN_F1>,
        <0x807F4E  KEY_FN_F2>,          <0x807F0A  KEY_FN_F3>,       <0x807F09  KEY_FN_F4>,
        <0x807F1C  KEY_FN_F5>,          <0x807F08  KEY_FN_F6>,       <0x807F0B  KEY_F1>,
        <0x807F18  KEY_F2>,             <0x807F00  KEY_F3>,          <0x807F0C  KEY_F4>,
        <0x807F4F  KEY_F5>,             <0x807F5E  KEY_F6>,          <0x807F43  KEY_F7>,
        <0x807F5F  KEY_F8>,             <0x807FFE  KEY_POWER2>,      <0x807FFF  KEY_OK>,
        //RC5 Remote Control
        <0x150C  KEY_POWER>,          <0x153F  KEY_AUX>,         <0x141D  KEY_MEDIA_REPEAT>,
        <0x141C  KEY_SHUFFLE>,        <0x100D  KEY_MUTE>,        <0x104F  KEY_F4>,
        <0x143F  KEY_F1>,             <0x112D  KEY_F2>,          <0x112E  KEY_F3>,
        <0x1010  KEY_VOLUMEUP>,       <0x1011  KEY_VOLUMEDOWN>,  <0x1521  KEY_PREVIOUSSONG>,
        <0x1520  KEY_NEXTSONG>,       <0x1536  KEY_PAUSE>,       <0x1535  KEY_PLAY>,
        <0x151F  KEY_BACK>,           <0x151E  KEY_FORWARD>,     <0x1063  KEY_MAX>,
        <0x1040  KEY_F6>,             <0x1120  KEY_CHANNELUP>,   <0x1121  KEY_CHANNELDOWN>;
    status = "ok";
};

IR DTS Configuration Description：

Attribute	Description	Value	Notes
compatible	Used to match the driver for driver registration	"sstar,ir"	Modification not allowed
reg	Used to set the register bank address	<0x1F007A00 0x200>	Modification not allowed
interrupts	Used to set interrupts and their properties	INT_FIQ_IR , INT_FIQ_IR_RC	Modification not allowed
clocks	Used to set the clock source	<&CLK_ir>	Modification not required
group	Used to set IR hardware group serial number	0	Modification not required
mode	Used to set the decode mode during initialization	½/¾, corresponding respectively to FULL/RAW/RC5/SW	Can be modified where necessary
protocol	Used to match the decoder protocol in SW mode	See Figure 5-5	Can be modified where necessary
vendor	Used to set the input id property of RC device	0x0000~0XFFFF, can be used to distinguish the remote controller	Can be modified depending on the controller setting
product	Used to set the input id property of RC device	0x0000~0XFFFF, can be used to distinguish the remote controller	Can be modified depending on the controller setting
rc-map-table	Code value transmitted by the remote controller and its corresponding input event code	0x00FFA8: Higher 16 bits are for customer code, and lower 8 bits are for key code; KEY_POWER: Input event codes	Different map table can be set for different controller
status	Used to enable or disable the IR driver	"ok" or "disable"	Can be modified where necessary

With reference to Figure 5-4 below, here are some notes on the rc-map-table configuration.

ADDR + IADDR: 0x807F, which means that the customer code is located at 0x807F.

CMD: 0x4A, which means that the key code is located at 0x4A.

Therefore, for the key value pair in the rc-map-table, the left column should be filled with the value 0x804A, and the right column should be filled with a certain input event code to be reported.

Figure 5-4: Remote Controller Signal Analyzed by Logic Analyzer

If SW mode is used, after configuring the native decoder of the kernel or the self-defined decoder through make menuconfig, you need to modify the following configuration in DTS:

If the user code of the attribute "rc-map-table" is complementary to the high 8-bit and low 8-bit, the native decoder of the kernel will process the reported user code and modify it as follows:
```
<0x00FFA8 KEY_POWER> -> <0x00A8 KEY_POWER>
```
Modify the "protocol" in DTS to match the decoder. Let's take NEC protocol as an example:
```
protocol = <9>;
```

The protocol options supported by kernel version 5.10 are illustrated below:

Figure 5-5: Options in rc_proto

6.3. Configure Padmux¶

To configure the padmux of IR, you only need to add the following code to the corresponding arch/arm/boot/dts/iford-xxxx-padmux.dtsi according to the selected pin (only one MODE needs to be configured):

<PAD_PM_GPIO8   PINMUX_FOR_PM_IR_IN_MODE_1  MDRV_PUSE_IR>;
<PAD_PM_GPIO3   PINMUX_FOR_PM_IR_IN_MODE_2  MDRV_PUSE_IR>;

The first column is the pin index number, which can be found in /drivers/sstar/hal/chip_name/pub/gpio.h;

The second column is the mode definition. In the m_hal_gpio_st_padmode_info_tbl array in /drivers/sstar/gpio/hal/chip_name/src/hal_pinmux.c, the multiplexing relationship of all pins is listed. You can query the array to check which multiplexing functions the pin supports;

The third column is the index name of the pin and the matching mode, which can be found in /drivers/sstar/include/drv_puse.h.

6.4. Module Usage Introduction¶

The IR driver will generate the corresponding event file in the /dev/input/ directory. You can obtain the key value decoded by the driver and reported to the input system by operating the event interface:

Get the key value in the Linux environment: Enter hexdump /dev/input/event0, and send a signal with the remote control to see the information in Figure 5-6 (the number of event nodes corresponds to the number of IR device groups configured).

Figure 5-6: Data Received Under /dev/input/event0
The IR decoding mode can be switched in user space. You can check the files under /sys/class/mstar. The number of IR devices corresponds to the number of IR nodes. To switch the IR decoding mode, go to echo [mode] > decode_mode to select the mode needed. The values allowed include 1 (FULL), 2 (RAW), 3 (RC5) and 4 (SW).

Figure 5-7: Cat /sys/class/mstar/ir0/decode_mode Results

6.5. Sample Code¶

Under the path driver/sstar/ir/ut, enter the command make and compile ut_ir.c. A file named ut_ir will be created under that path.

ut_ir.c mainly obtains the input event type and key value by reading the event interface, and transmits the information to the user state through struct input_event. Every time the remote control sends an IR signal, the event type of input_event will change in the following order: EV_MSC->EV_KEY->EV_SYN->EV_KEY->EV_SYN.

Type	Code	Value
EV_MSC	MSC_SCAN(0x4)	Code value
EV_SYN	SYN_REPORT (0x0)	0x0
EV_KEY	The key value corresponding to the code value in rc_map_table	1: Key down, 0： Key up

Copy the generated ut_ir file to the board and run it. Enter ./ut_ir [group][event][mode] [count], where count is the number of times the remote control button is pressed. For example, enter ./ut_ir 0 event0 1 5 to test the function when the IR0 decoding mode is FULL. Press the button of the remote control facing the IR, and the log prints the read press and lift signal and the related key value. As shown in Figure 5-8, the remote control test results, where EV_MSC is the code value of the remote control signal after IR decoding, and the EV_KEY_DONW/EV_KEY_UP value is the key value after the code value is converted through the rc-map-table.

Figure 5-8: Run ut_ir and Receive Signal Log

7. API Refernece¶

No external API available at the moment.

8. FAQ¶

If the remote control does not trigger the Input event after being pressed, that is, hexdump /dev/input/event0 does not print any information, you can check from the following aspects:

8.1 IR Driver Cannot Receive IR Signal¶

Check if padmux is configured. See 5.1. Configuring Padmux for details.
Check if kernel config is configured. See 5.2. Configuring Kennel Config for details.
Check if the status of DTS IR node is ok.
Check if there is a place that needs to be shorted in the IR Receiver within the hardware schematic (e.g. JP55 in Figure 5-14).

Figure 5-9: IR Hardware Schematic
Check the waveform of the remote control to judge whether the IR_IN signal conforms to the NEC, RC5 format and whether the current decoding mode matches the source signal.

8.2 EVENT Event Are not Triggered¶

If neither the EV_MISC event nor the EV_KEY event is triggered, check the rc_map_table of DTS to see if the code value in the left column of the key-value pair is consistent with the one transmitted by the remote control.
If the EV_MISC event is triggered but the EV_KEY event is not triggered, check the rc_map_table of DTS to see if the code value in the left column of the key-value pair corresponds to the input event code in the right column one by one and is supported by the kernel.
If the decoding mode is SW mode, check if the decoder of the protocol to which the remote control belongs is compiled.