Add api doc of en

doc/en/mainpage.md

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+# MYNT EYE SDK {#mainpage}
+
+* <a class="el" href="annotated.html">API Classes</a>
+* <a class="el" href="modules.html">API Modules</a>
+  * \link enumerations Enumerations\endlink
+  * \link datatypes Datatypes\endlink
+  * \link utils Utiliities\endlink
+  * \link calibration Intrinsics & Extrinsics\endlink
+* <span style="font-weight:bold">Device Specifications</span>
+  * @subpage specs_data
+  * @subpage specs_ctrl

doc/en/spec_control_api.md

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+# Control Protocols {#spec_control_api}
+
+There are two control modes, one is through UVC standard protocol, the other is through UVC custom protocol with extension unit.
+
+## Standard Protocol
+
+| Name | Field | Bytes | Default | Min | Max | Stored | Flash Address | Note |
+| :--- | :---- | :---- | :------ | :-- | :-- | :----- | :------------ | :--- |
+| Gain | gain | 2 | 24 | 0 | 48 | √ | 0x12 | valid if manual-exposure |
+| Brightness | brightness/exposure_time | 2 | 120 | 0 | 240 | √ | 0x14 | valid if manual-exposure |
+| Contrast | contrast/black_level_calibration | 2 | 127 | 0 | 255 | √ | 0x10 | valid if manual-exposure |
+
+## Custom Protocol
+
+| Name | Field | Bytes | Default | Min | Max | Stored | Flash Address | Channel | Note |
+| :--- | :---- | :---- | :------ | :-- | :-- | :----- | :------------ | :------ | :----- |
+| Frame rate | frame_rate | 2 | 25 | 10 | 60 | √ | 0x21 | XU_CAM_CTRL | values: {10,15,20,25,30,35,40,45,50,55,60} |
+| IMU frequency | imu_frequency | 2 | 200 | 100 | 500 | √ | 0x23 | XU_CAM_CTRL | values: {100,200,250,333,500} |
+| Exposure mode | exposure_mode | 1 | 0 | 0 | 1 | √ | 0x0F | XU_CAM_CTRL | 0: enable auto-exposure; 1: manual-exposure |
+| Max gain | max_gain | 2 | 48 | 0 | 48 | √ | 0x1D | XU_CAM_CTRL | valid if auto-exposure |
+| Max exposure time | max_exposure_time | 2 | 240 | 0 | 240 | √ | 0x1B | XU_CAM_CTRL | valid if auto-exposure |
+| Desired brightness | desired_brightness | 2 | 192 | 0 | 255 | √ | 0x19 | XU_CAM_CTRL | valid if auto-exposure |
+| IR control | ir_control | 1 | 0 | 0 | 160 | × | - | XU_CAM_CTRL | |
+| HDR mode | hdr_mode | 1 | 0 | 0 | 1 | √ | 0x1F | XU_CAM_CTRL | 0: 10-bit; 1: 12-bit |
+| Zero drift calibration | zero_drift_calibration | | - | - | - | × | - | XU_HALF_DUPLEX | |
+| Erase chip | erase_chip | | - | - | - | × | - | XU_HALF_DUPLEX | |

doc/en/spec_control_channel.md

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+# Control Channels {#spec_control_channel}
+
+| Name | Field | Address | Bandwidth | Node |
+| :----- | :----- | :----- | :----- | :----- |
+| Camera control channel | XU_CAM_CTRL_CHANNEL | 1 | 3 | |
+| Half-Duplex channel | XU_HALF_DUPLEX_CHANNEL | 2 | 20 | |
+| IMU write channel | XU_IMUDATA_WRITE_CHANNEL | 3 | 5 | |
+| IMU read channel | XU_IMUDATA_READ_CHANNEL | 4 | 2000 | |
+| File channel | XU_FILE_CHANNEL | 5 | 2000 | |
+
+## Camera Control Channel
+
+The channel provides get, set and query (min, max, default).
+
+## Half-Duplex Channel
+
+The channel only provides set, such as zero drift correction.
+
+## IMU Channel
+
+The channel is used to request and response IMU data, see @ref spec_imu_data.
+
+## File Channel
+
+The channel is used to read and write device information, image params, and IMU params.
+
+| Name | Header | Size | File | Checksum |
+| :--- | :- | :--- | :--- | :-------- |
+| Bytes | 1 | 2 | - | 1 |
+| Type | uint8_t | uint16_t | - | uint8_t |
+| Description | Flags | Content size | Content data | Checksum, XOR of all content bytes |
+
+| Header Bit Subscript | Description |
+| :------------------- | :---------- |
+| 0 | Device information |
+| 1 | Image params |
+| 2 | IMU params |
+| 3~6 | Undefined |
+| 7 | 0: Get; 1: Set |
+
+### File Content Packet
+
+| Name | ID | Size | Content |
+| :--- | :- | :--- | :------ |
+| Bytes | 1 | 2 | - |
+| Type | uint8_t | uint16_t | - |
+| Description | Content ID | Content size | Content data |
+
+| File | ID | Max Size |
+| :--- | :- | :------- |
+| Device information | 1 | 250 |
+| Image params | 2 | 250 |
+| IMU params | 4 | 500 |

doc/en/spec_hardware_info.md

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+# Device Information {#spec_hardware_info}
+
+| Name | Field | Fixed Value | USB Descriptor | UVC Extension Unit | Bytes | Note |
+| :----- | :----- | :-------- | :-------------- | :----------------- | :-------- | :----- |
+| VID | vid | 0x04B4 | √ | × | 2 | |
+| PID | pid | 0x00F9 | √ | × | 2 | |
+| Device name | name | MYNT-EYE-? | √ | √ Get | 16 | MYNT-EYE-S1000 |
+| Serial number | serial_number | - | √ | √ Get | 16 | |
+| Firmware version | firmware_version | - | √ | √ Get | 2 | major,minor |
+| Hardware version | hardware_version | - | × | √ Get | 3 | major,minor,flag |
+| Spec version | spec_version | - | × | √ Get | 2 | major,minor |
+| Lens type | lens_type | - | × | √ Get/Set | 4 | vendor(2),product(2); default: 0 |
+| IMU type | imu_type | - | × | √ Get/Set | 4 | vendor(2),product(2); default: 0 |
+| Nominal baseline | nominal_baseline | - | × | √ Get/Set | 2 | unit: mm; default: 0 |

doc/en/spec_image_data.md

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+# Image Data {#spec_image_data}
+
+| Name | Field | Unit | Bytes | Note |
+| :----- | :----- | :----- | :-------- | :----- |
+| Frame ID | frame_id | - | 2 | uint16_t; [0,65535] |
+| Timestamp | timestamp | 10 us | 4 | uint32_t |
+| Exposure Time | exposure_time | 10 us | 2 | uint16_t |
+
+## Image Packet
+
+| Name | Header | Size | Frame ID | Timestamp | Exposure Time | Checksum |
+| :--- | :----- | :--- | :------- | :-------- | :------------ | :------- |
+| Bytes | 1 | 1 | 2 | 4 | 2 | 1 |
+| Type | uint8_t | uint8_t | uint16_t | uint32_t | uint16_t | uint8_t |
+| Description | 0x3B | 0x08, content size | Frame ID | Timestamp | Exposure time | Checksum, XOR of all content bytes |
+
+* The image packet will be dropped, if checksum is incorrect.
+* The accuracy of the time unit: 0.01 ms / 10 us.
+  * The timestamp could indicate 11.9 hours, it will accumulate again after overflow.
+* The timestamp accumulation starts from the time of power-on, instead of opening.

doc/en/spec_image_params.md

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+# Image Params {#spec_image_params}
+
+## Image Intrinsics
+
+| Name | Field | Unit | Bytes | Note |
+| :----- | :----- | :----- | :-------- | :----- |
+| Image width | width | px | 2 | uint16_t; [0,65535] |
+| Image height | height | px | 2 | uint16_t; [0,65535] |
+| Focal length | fx | - | 8 | double |
+| ^ | fy | - | 8 | double |
+| Principal point | cx | - | 8 | double |
+| ^ | cy | - | 8 | double |
+| Distortion model | model | - | 1 | uint8_t; pinhole,... |
+| Distortion coefficients | coeffs[5] | - | 40 | double; k1,k2,p1,p2,k3 |
+
+## Image Extrinsics
+
+Transformation matrix from left image to right image.
+
+| Name | Field | Unit | Bytes | Note |
+| :----- | :----- | :----- | :-------- | :----- |
+| Rotation matrix | rotation[3][3] | - | 72 | double |
+| Translation vector | translation[3] | - | 24 | double |

doc/en/spec_imu_data.md

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+# IMU Data {#spec_imu_data}
+
+## IMU Request Packet
+
+| Name | Header | Serial Number |
+| :--- | :----- | :------------ |
+| Bytes | 1 | 4 |
+| Type | uint8_t | uint32_t |
+| Description | 0x5A | First request should be 0, otherwise the last one |
+
+## IMU Response Packet
+
+The IMU response packet contains multiple IMU packets, and each IMU packet contains multiple IMU segments.
+
+| Name | Header | State | Size | IMU Packets | Checksum |
+| :--- | :----- | :---- | :--- | :---------- | :------- |
+| Bytes | 1 | 1 | 2 | ... | 1 |
+| Type | uint8_t | uint8_t | uint16_t | - | uint8_t |
+| Description | 0x5B | 0 is success, others are failed | Content size | IMU packets | Checksum, XOR of all content bytes |
+
+### IMU Packet
+
+The IMU packet is an array of IMU datas.
+
+| Name | Serial Number | Timestamp | Count | IMU Datas |
+| :--- | :------------ | :-------- | :---- | :-------- |
+| Bytes | 4 | 4 | 1 | ... |
+| Type | uint32_t | uint32_t | uint8_t | - |
+| Description | Serial number | IMU basic timestamp | The number of IMU datas | IMU datas |
+
+### IMU Segment
+
+| Name | Offset | Frame ID | Accelerometer | Temperature | Gyroscope |
+| :--- | :----- | :------- | :------------ | :---------- | :-------- |
+| Bytes | 2 | 2 | 6 | 2 | 6 |
+| Type | int16_t | uint16_t | int16_t * 3 | int16_t | int16_t * 3 |
+| Description | The timestamp offset | Image frame ID | Accel x,y,z values | IMU temperature | Gyro x,y,z values |
+
+* Formula for converting the accel & gyro values to real ones: **real = data * range / 0x10000** .
+  * ``accel`` default ``range`` is **8 g**, ``gyro`` default ``range`` is **1000 deg/s**.
+* Formula for converting the temperature to real value: **real = data / ratio + offset** .
+  * default ``ratio`` is **326.8**, default ``offset`` is **25℃**.

doc/en/spec_imu_params.md

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+# IMU Params {#spec_imu_params}
+
+## IMU Intrinsics
+
+| Name | Field | Unit | Bytes | Note |
+| :----- | :----- | :----- | :-------- | :----- |
+| Scale matrix | acc_scale[3][3] | - | 72 | double |
+| ^ | gyro_scale[3][3] | - | 72 | double |
+| Zero-drift | acc_drift[3] | - | 24 | double |
+| ^ | gyro_drift[3] | - | 24 | double |
+| Noise density | acc_noise[3] | - | 24 | double |
+| ^ | gyro_noise[3] | - | 24 | double |
+| Random walk | acc_bias[3] | - | 24 | double |
+| ^ | gyro_bias[3] | - | 24 | double |
+
+## IMU Extrinsics
+
+Transformation matrix from left image to IMU.
+
+| Name | Field | Unit | Bytes | Note |
+| :----- | :----- | :----- | :-------- | :----- |
+| Rotation matrix | rotation[3][3] | - | 72 | double |
+| Translation vector | translation[3] | - | 24 | double |

doc/en/specs_ctrl.md

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+# Device Control Specification {#specs_ctrl}
+
+* @subpage spec_control_api
+* @subpage spec_control_channel

doc/en/specs_data.md

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+# Device Data Specification {#specs_data}
+
+* @subpage spec_hardware_info
+* @subpage spec_image_params
+* @subpage spec_imu_params
+* @subpage spec_image_data
+* @subpage spec_imu_data