High-Definition Multimedia Interface (HDMI) is an audio/video transmission protocol released by Hitachi, Panasonic, Philips, Silicon Image, Sony, Thomson, and Toshiba.
## Overview
HDMI works in master/slave mode and usually has a source and a sink.
### HDMI
The HDMI APIs provide a set of common functions for HDMI transmission, including:
- High-definition multimedia interface (HDMI) is an interface for transmitting audio and video data from a source device, such as a DVD player or set-top box (STB), to a sink device, such as a TV or display.
- HDMI works in master/slave mode and usually has a source and a sink.
- The HDMI APIs provide a set of common functions for HDMI transmission, including:
- Opening and closing an HDMI controller
- Starting and stopping HDMI transmission
- Setting audio, video, and High Dynamic Range (HDR) attributes, color depth, and AV mute
- Reading the raw Extended Display Identification Data (EDID) from a sink
- Registering and unregistering a callback for HDMI hot plug detect (HPD)
- Opening and closing an HDMI controller
- Starting and stopping HDMI transmission
- Setting audio, video, and High Dynamic Range (HDR) attributes, color depth, and AV mute
- Reading the raw Extended Display Identification Data (EDID) from a sink
- Registering and unregistering a callback for HDMI hot plug detect (HPD).
[Figure 1](#fig1) shows the HDMI physical connection.
HDMI is an audio and video transmission protocol released by Hitachi, Panasonic, Philips, Silicon Image, Sony, Thomson, and Toshiba. The transmission process complies with the Transition-minimized Differential Signaling (TMDS).
- TMDS is used to transmit audio, video, and various auxiliary data.
- Display data channel (DDC) allows the TX and RX ends to obtain the sending and receiving capabilities. However, the HDMI only needs to unidirectionally obtain the capabilities of the RX end (display).
- Consumer Electronics Control (CEC) enables interaction between the HDMI TX and RX devices.
- Fixed rate link (FRL) allows the maximum TMDS bandwidth to be increased from 18 Gbit/s to 48 Gbit/s.
- High-bandwidth Digital Content Protection (HDCP) prevents copying of digital audio and video content being transmitted across devices.
- Extended Display Identification Data (EDID), usually stored in the display firmware, provides the vendor information, EDID version, maximum image size, color settings, vendor pre-settings, frequency range limit, display name, and serial number.
## Available APIs<a name="section2"></a>
### Working Principles
The HDMI source end provides +5 V and GND for DDC and CEC communication. Through the DDC, the source end obtains the sink end parameters, such as the RX capabilities. The CEC is optional. It is used to synchronize the control signals between the source and sink ends to improve user experience. There are four TMDS channels between the HDMI source and sink ends. The TMDS clock channel provides clock signals for TMDS, and the other three channels transmit audio, video, and auxiliary data. HPD is the hot plug detect port. When the sink end is connected, the source end responds by using an interrupt program.
The figure below shows the HDMI physical connection.
Currently, the HDMI module supports only the kernels (LiteOS) of mini and small systems.
## Development Guidelines
### When to Use
HDMI features high transmission rate, wide transmission bandwidth, high compatibility, and can transmit uncompressed audio and video signals. Compared with the traditional full analog interface, HDMI simplifies connection between devices and provides HDMI-specific intelligent features, which are ideal for high-quality audio and video transmission of small-sized devices.
High-Definition Multimedia Interface (HDMI) is an audio/video transmission protocol released by Hitachi, Panasonic, Philips, Silicon Image, Sony, Thomson, and Toshiba. It is used to transmit audio or video data from an audio or video source device, such as a DVD player or STB, to a sink device, such as a TV or monitor. The transmission process complies with the Transition Minimized Differential Signaling (TMDS) protocol.
### HDMI
High-definition multimedia interface (HDMI) is an interface for transmitting audio and video data from a source device, such as a DVD player or set-top box (STB), to a sink device, such as a TV or display.
### Basic Concepts
HDMI is an audio and video transmission protocol released by Hitachi, Panasonic, Philips, Silicon Image, Sony, Thomson, and Toshiba. The transmission process complies with the Transition Minimized Differential Signaling (TMDS) protocol.
- TMDS is used to transmit audio, video, and various auxiliary data.
- Display data channel (DDC) allows the TX and RX ends to obtain the sending and receiving capabilities. However, the HDMI only needs to unidirectionally obtain the capabilities of the RX end (display).
- Consumer Electronics Control (CEC) enables interaction between the HDMI TX and RX devices.
- Fixed rate link (FRL) allows the maximum TMDS bandwidth to be increased from 18 Gbit/s to 48 Gbit/s.
- High-bandwidth Digital Content Protection (HDCP) prevents copying of digital audio and video content being transmitted across devices.
### Working Principles
In the HDF, the HDMI module uses the independent service mode for API adaptation. In this mode, each device independently publishes a device service to process external access requests. After receiving an access request, the device manager extracts the parameters in the request to call the internal method of the target device. In the independent service mode, the service management capabilities of the HDFDeviceManager can be directly used. However, you need to configure a node for each device, which increases the memory usage.
**Figure 1** Independent service mode<aname="fig1"></a>
Currently, the HDMI module supports only the kernels (LiteOS) of mini and small systems.
## Development Guidelines
### Use Cases
HDMI features high transmission rate, wide transmission bandwidth, high compatibility, and can transmit uncompressed audio and video signals. Compared with the traditional full analog interface, HDMI simplifies connection between devices and provides HDMI-specific intelligent features, which are ideal for high-quality audio and video transmission of small-sized devices.
| hardWareInit | **cntlr**: structure pointer to an HDMI controller at the core layer.| –| –| Initializes the HDMI hardware.|
| hardWareStatusGet | **cntlr**: structure pointer to an HDMI controller at the core layer.<br>| **status**: pointer to the HDMI hardware status.| –| Obtains the HDMI hardware status. |
| controllerReset | **cntlr**: structure pointer to an HDMI controller at the core layer.| – | –| Resets an HDMI controller. |
| hotPlugStateGet | **cntlr**: structure pointer to an HDMI controller at the core layer. | – | **bool**: HDMI hot-plug status.| Obtains the HDMI hot-plug status. |
| hotPlugInterruptStateGet | **cntlr**: structure pointer to an HDMI controller at the core layer. | – | **bool**: HDMI hot-plug interrupt status.| Obtains the HDMI hot-plug interrupt status. |
| lowPowerSet | **cntlr**: structure pointer to an HDMI controller at the core layer.<br>**enable**: whether to enable low power consumption.| – | –| Enables or disables low power consumption.|
| tmdsModeSet | **cntlr**: structure pointer to an HDMI controller at the core layer.<br>**mode**: TMDS mode.| – | –| Sets the TMDS mode. |
|tmdsConfigSet|**cntlr**: structure pointer to an HDMI controller at the core layer.<br>**mode**: TMDS parameters.|–|HDF_STATUS|Sets TMDS parameters.|
|infoFrameEnable|**cntlr**: structure pointer to an HDMI controller at the core layer.<br>**infoFrameType**: packet type.<br>**enable**: whether to enable infoFrame.|–|–|Enables or disables infoFrame.|
|infoFrameSend|**cntlr**: structure pointer to an HDMI controller at the core layer.<br>**infoFrameType**: packet type.<br>**data**: pointer to infoFrame data.<br>**len**: data length.|–|HDF_STATUS|Sends an infoFrame.|
|cecMsgSend|**cntlr**: structure pointer to an HDMI controller at the core layer.<br>**msg**: pointer to the CEC message|–|HDF_STATUS|Sends a CEC message.|
|audioPathEnable|**cntlr**: structure pointer to an HDMI controller at the core layer.<br>**enable**: whether to enable the audio path.|–|–|Enables or disables the audio path.|
|audioPathSet|**cntlr**: structure pointer to an HDMI controller at the core layer.<br>**config**: pointer to the audio path configuration.|–|–|Sets the audio path.|
|phyOutputEnable|**cntlr**: structure pointer to an HDMI controller at the core layer.<br>**enable**: whether to enable the physical layer output.|–|–|Enables or disables the physical layer output.|
|phyOutputSet|**cntlr**: structure pointer to an HDMI controller at the core layer.<br>**cfg**: pointer to the physical layer configuration.|–|–|Sets the physical layer information.|
|blackDataSet|**cntlr**: structure pointer to an HDMI controller at the core layer.<br>**enable**: whether to enable the black screen.|–|–|Sets the black screen.|
|videoMuteEnable|**cntlr**: structure pointer to an HDMI controller at the core layer.<br>**enable**: whether to enable the video mute feature.|–|–|Enables or disables the video mute feature.|
|videoPathSet|**cntlr**: structure pointer to an HDMI controller at the core layer.<br>**attr**: pointer to the video path configuration.|–|–|Sets the video path.|
|audioMuteEnable|**cntlr**: structure pointer to an HDMI controller at the core layer.<br>**enable**: whether to enable the audio mute feature.|–|–|Enables or disables the audio mute feature.|
|avmuteSet|**cntlr**: structure pointer to an HDMI controller at the core layer.<br>**enable**: whether to enable the AV mute feature.|–|–|Enables or disables the AV mute feature.|
|ddcTransfer|**cntlr**: structure pointer to an HDMI controller at the core layer.<br>**ddcCfg**: pointer to the DDC configuration.|**ddcCfg**: DDC configuration.|HDF_STATUS|Reads and writes data through the DDC.|
|scdcSourceScrambleGet|**cntlr**: structure pointer to an HDMI controller at the core layer.|–|Scrambling status of the source.|Obtains the scrambling status of the source.|
|scdcSourceScrambleSet|**cntlr**: structure pointer to an HDMI controller at the core layer.<br>**enable**: whether to enable the scrambling for the source.|–|HDF_STATUS|Enables or disable scrambling for the source.|
|frlEnable|**cntlr**: structure pointer to an HDMI controller at the core layer.<br>**enable**: whether to enable the FRL.|–|HDF_STATUS|Enables or disables the FRL.|
|audioNctsSet|**cntlr**: structure pointer to an HDMI controller at the core layer.<br>**cfg**: pointer to the N/CTS configuration.|–|HDF_STATUS|Sets the audio N/CTS information.|
|frlTrainingConfigSet|**cntlr**: structure pointer to an HDMI controller at the core layer.<br>**cfg**: pointer to the FRL training configuration.|–|–|Sets FRL training information.|
|frlTrainingStart|**cntlr**: structure pointer to an HDMI controller at the core layer.|–|–|Starts FRL training.|
|frlGetTriningRslt|**cntlr**: structure pointer to an HDMI controller at the core layer.|**rslt**: FRL training result.|–|Obtains the FRL training result.|
|hdcpRegInit|**cntlr**: structure pointer to an HDMI controller at the core layer.|–|–|Initializes registers related to the High-bandwidth Digital Content Protection (HDCP) process.|
|hdcpGenerateAksvAndAn|**cntlr**: structure pointer to an HDMI controller at the core layer.|–|HDF_STATUS|Generates the **Aksv** and **An** in the HDCP process.|
|hdcpOptReg|**cntlr**: structure pointer to an HDMI controller at the core layer.<br>**type**: operation type.<br>**data**: register data.<br>**len**: data length.|**data**: register data.|HDF_STATUS|Reads or writes the registers during the HDCP process.|
|hdrTimerSet|**cntlr**: structure pointer to an HDMI controller at the core layer.<br>**config**: pointer to the timer configuration|–|–|Sets the HDR-related timer.|
**Table 1** APIs for the members in the HdmiCntlrOps structure
| hardWareInit | **cntlr**: structure pointer to an HDMI controller at the core layer.| –| –| Initializes HDMI hardware.|
| hardWareStatusGet | **cntlr**: structure pointer to an HDMI controller at the core layer.<br/>| **status**: pointer to the HDMI hardware status.| –| Obtains the HDMI hardware status.|
| controllerReset | **cntlr**: structure pointer to an HDMI controller at the core layer.| –| –| Resets an HDMI controller.|
| hotPlugStateGet | **cntlr**: structure pointer to an HDMI controller at the core layer.| –| **bool**: HDMI hot-plug status.| Obtains the HDMI hot-plug status.|
| hotPlugInterruptStateGet | **cntlr**: structure pointer to an HDMI controller at the core layer.| –| **bool**: HDMI hot-plug interrupt status.| Obtains the HDMI hot-plug interrupt status.|
| lowPowerSet | **cntlr**: structure pointer to an HDMI controller at the core layer.<br/>**enable**: whether to enable low power consumption.| –| –| Enables or disables low power consumption.|
| tmdsModeSet | **cntlr**: structure pointer to an HDMI controller at the core layer. <br/>**mode**: TMDS mode.| –| –| Sets the TMDS mode. |
|tmdsConfigSet|**cntlr**: structure pointer to an HDMI controller at the core layer. <br/>**mode**: TMDS parameters.|–|HDF_STATUS|Sets TMDS parameters.|
|infoFrameEnable|**cntlr**: structure pointer to an HDMI controller at the core layer. <br/>**infoFrameType**: packet type.<br/>**enable**: whether to enable infoFrame.|–|–|Enables or disables infoFrame.|
|infoFrameSend|**cntlr**: structure pointer to an HDMI controller at the core layer. <br/>**infoFrameType**: packet type.<br/>**data**: pointer to infoFrame data.<br/>**len**: data length.|–|HDF_STATUS|Sends an infoFrame.|
|cecMsgSend|**cntlr**: structure pointer to an HDMI controller at the core layer. <br/>**msg**: pointer to the Consumer Electronics Control (CEC) message.|–|HDF_STATUS|Sends a CEC message.|
|audioPathEnable|**cntlr**: structure pointer to an HDMI controller at the core layer. <br/>**enable**: whether to enable the audio path.|–|–|Enables or disables the audio path.|
|audioPathSet|**cntlr**: structure pointer to an HDMI controller at the core layer. <br/>**config**: pointer to the audio path configuration.|–|–|Sets the audio path.|
|phyOutputEnable|**cntlr**: structure pointer to an HDMI controller at the core layer.<br/>**enable**: whether to enable the physical layer output.|–|–|Enables or disables the physical layer output.|
|phyOutputSet|**cntlr**: structure pointer to an HDMI controller at the core layer. <br/>**cfg**: pointer to the physical layer configuration.|–|–|Sets the physical layer information.|
|blackDataSet|**cntlr**: structure pointer to an HDMI controller at the core layer. <br/>**enable**: whether to enable the black screen.|–|–|Sets the black screen.|
|videoMuteEnable|**cntlr**: structure pointer to an HDMI controller at the core layer. <br/>**enable**: whether to enable the video mute feature.|–|–|Enables or disables the video mute feature.|
|videoPathSet|**cntlr**: structure pointer to an HDMI controller at the core layer. <br/>**attr**: pointer to the video path configuration.|–|–|Sets the video path.|
|audioMuteEnable|**cntlr**: structure pointer to an HDMI controller at the core layer. <br/>**enable**: whether to enable the audio mute feature.|–|–|Enables or disables the audio mute feature.|
|avmuteSet|**cntlr**: structure pointer to an HDMI controller at the core layer.<br/>**enable**: whether to enable the AV mute feature.|–|–|Enables or disables the AV mute feature.|
|ddcTransfer|**cntlr**: structure pointer to an HDMI controller at the core layer. <br/>**ddcCfg**: pointer to the display data channel (DDC) configuration.|**ddcCfg**: DDC configuration.|HDF_STATUS|Reads and writes data through the DDC.|
|scdcSourceScrambleGet|**cntlr**: structure pointer to an HDMI controller at the core layer.|–|Scrambling status of the source.|Obtains the scrambling status of the source.|
|scdcSourceScrambleSet|**cntlr**: structure pointer to an HDMI controller at the core layer. <br/>**enable**: whether to enable scrambling for the source.|–|HDF_STATUS|Enables or disable scrambling for the source.|
|frlEnable|**cntlr**: structure pointer to an HDMI controller at the core layer. <br/>**enable**: whether to enable the fixed rate link (FRL).|–|HDF_STATUS|Enables or disables the FRL.|
|audioNctsSet|**cntlr**: structure pointer to an HDMI controller at the core layer. <br/>**cfg**: pointer to the N/CTS configuration.|–|HDF_STATUS|Sets the audio N/CTS information.|
|frlTrainingConfigSet|**cntlr**: structure pointer to an HDMI controller at the core layer. <br/>**cfg**: pointer to the FRL training configuration.|–|–|Sets FRL training information.|
|frlTrainingStart|**cntlr**: structure pointer to an HDMI controller at the core layer.|–|–|Starts FRL training.|
|frlGetTriningRslt|**cntlr**: structure pointer to an HDMI controller at the core layer.|**rslt**: FRL training result.|–|Obtains the FRL training result.|
|hdcpRegInit|**cntlr**: structure pointer to an HDMI controller at the core layer.|–|–|Initializes registers related to the High-bandwidth Digital Content Protection (HDCP) process.|
|hdcpGenerateAksvAndAn|**cntlr**: structure pointer to an HDMI controller at the core layer.|–|HDF_STATUS|Generates the **Aksv** and **An** in the HDCP process.|
|hdcpOptReg|**cntlr**: structure pointer to an HDMI controller at the core layer. <br/>**type**: operation type. <br/>**data**: pointer to the register data. <br/>**len**: data length.|**data**: register data.|HDF_STATUS|Reads or writes the registers in the HDCP process.|
|hdrTimerSet|**cntlr**: structure pointer to an HDMI controller at the core layer. <br/>**config**: pointer to the timer configuration.|–|–|Sets the HDR-related timer.|
## How to Develop<a name="3"></a>
### How to Develop
The HDMI module adaptation involves the following steps:
1. Instantiate the driver entry.
- Instantiate the driver entry.
- Instantiate the **HdfDriverEntry** structure.
- Call **HDF_INIT** to register the **HdfDriverEntry** instance with the HDF.
2. Configure attribute files.
- Configure attribute files.
- Add the **deviceNode** information to the **device_info.hcs** file.
- (Optional) Add the **hdmi_config.hcs** file.
3. Instantiate the HDMI controller object.
- Instantiate the HDMI controller object.
- Initialize **HdmiCntlr**.
- Instantiate **HdmiCntlrOps** in **HdmiCntlr**. For details, see [Available APIs](#available_apis).
- Instantiate **HdmiCntlrOps** in **HdmiCntlr**.
## Development Example<a name="4"></a>
1. Instantiate the driver entry.
1. Instantiate the driver entry. The driver entry must be a global variable of the **HdfDriverEntry** type (defined in **hdf\_device\_desc.h**), and the value of **moduleName** must be the same as that in **device\_info.hcs**. In the HDF, the start address of each **HdfDriverEntry** object of all loaded drivers are collected to form a segment address space similar to an array for the upper layer to invoke.
The driver entry must be a global variable of the **HdfDriverEntry** type (which is defined in **hdf_device_desc.h**), and the value of **moduleName** must be the same as that in **device_info.hcs**. In the HDF, the start address of each **HdfDriverEntry** object of all loaded drivers is collected to form a segment address space similar to an array for the upper layer to invoke.
Generally, the HDF calls the **Bind** function and then the **Init** function to load a driver. If **Init** fails to be called, the HDF calls **Release** to release driver resources and exit.
Generally, the HDF calls the **Bind()** function and then the **Init()** function to load a driver. If **Init()** fails to be called, the HDF calls **Release()** to release driver resources and exit.
HDMI driver entry reference:
...
...
@@ -128,7 +154,9 @@ The HDMI module adaptation involves the following steps:
HDF_INIT(g_hdmiDriverEntry); // Call HDF_INIT to register the driver entry with the HDF.
```
2. Add **deviceNode** to the **device_info.hcs** file, and configure the device attributes in the **hdmi\_config.hcs** file. The **deviceNode** information is related to registration of the driver entry. The device attribute values are closely related to the driver implementation and the default values or restriction ranges of the **HdmiCntlr** members at the core layer.
2. Configure attribute files.
Add **deviceNode** to the **device_info.hcs** file, and configure the device attributes in the **hdmi\_config.hcs** file. The **deviceNode** information is related to registration of the driver entry. The device attribute values are closely related to the driver implementation and the default values or restriction ranges of the **HdmiCntlr** members at the core layer.
Configure HDMI controller information from the first node. This node specifies a type of HDMI controllers rather than a specific HDMI controller. In this example, there is only one HDMI controller. If there are multiple HDMI controllers, you need to add the **deviceNode** information to the **device\_info** file and add the corresponding device attributes to the **hdmi\_config** file.
...
...
@@ -200,14 +228,15 @@ The HDMI module adaptation involves the following steps:
}
```
3. Initialize the **HdmiCntlr** object at the core layer, including initializing the vendor custom structure (passing parameters and data) and instantiating the **HdmiCntlrOps** (used to call the underlying functions of the driver). The **HdfDriverEntry** member functions (**Bind**, **Init**, and **Release**) must be implemented in this step.
Initialize the **HdmiCntlr** object at the core layer, including initializing the vendor custom structure (passing parameters and data) and instantiating the **HdmiCntlrOps** (used to call the underlying functions of the driver). The **HdfDriverEntry** member functions (**Bind**, **Init**, and **Release**) must be implemented in this step.
> To the driver, the custom structure carries parameters and data. The values in the **hdmi_config.hcs** file are read by the HDF, and structure members are initialized by **DeviceResourceIface**. Some important values (such as the device number and bus number) are also passed to the **HdmiCntlr** object at the core layer.
```c
struct HdmiAdapterHost {
struct HdmiCntlr *cntlr; // (Mandatory) Control object at the core layer. The details are as follows:
...
...
@@ -216,8 +245,8 @@ The HDMI module adaptation involves the following steps:
uint32_t regSize; // (Mandatory) Register bit width.
uint32_t irqNum; // (Mandatory) IRQ number.
};
/* HdmiCntlr is the controller structure at the core layer. Its members are assigned with values by using the Init function. */
/* HdmiCntlr is the controller structure at the core layer. Its members are assigned with values by using the Init() function. */
struct HdmiCntlr {
struct IDeviceIoService service;
struct HdfDeviceObject *hdfDevObj;
...
...
@@ -242,9 +271,9 @@ The HDMI module adaptation involves the following steps:
void *priv;
};
```
-**(Important)** Instantiate the callback structure **HdmiCntlrOps** in **HdmiCntlr**.
@@ -283,29 +312,29 @@ The HDMI module adaptation involves the following steps:
.hdrTimerSet = HdmiAdapterHdrTimerSet,
};
```
-**Bind** function
> Input parameter:
> **HdfDeviceObject**, an interface parameter exposed by the driver, contains the .hcs configuration.
>
> Return value:
> **HDF\_STATUS** (The following table lists some states. For more details, see **HDF\_STATUS** definition in the **/drivers/framework/include/utils/hdf\_base.h file**.)
|State|Description|
- **Bind()** function
**Input parameter**:
**HdfDeviceObject**, an interface parameter exposed by the driver, contains the .hcs configuration.
**Return value**:
**HDF\_STATUS** (The following table lists some states. For more details, see **HDF\_STATUS** definition in the **/drivers/framework/include/utils/hdf\_base.h file**.)
> Initializes the custom structure object **HdmiAdapterHost** and **HdmiCntlr**, and calls the **HdmiCntlrAdd** function to add the HDMI controller to the core layer.
>
> The **HdmiCntlr**, **HdmiAdapterHost**, and **HdfDeviceObject** assign values with each other so that other functions can be converted successfully.
**Function description**:
Initializes the custom structure object **HdmiAdapterHost** and **HdmiCntlr**, and calls the **HdmiCntlrAdd** function to add the HDMI controller to the core layer.
The **HdmiCntlr**, **HdmiAdapterHost**, and **HdfDeviceObject** assign values with each other so that other functions can be converted successfully.
> **HdfDeviceObject**, an interface parameter exposed by the driver, contains the .hcs configuration.
>
> Return value:
> –
>
> Function description:
> Releases the memory and deletes the controller. This function assigns a value to the **Release** API in the driver entry structure. If the HDF fails to call the **Init** function to initialize the driver, the **Release** function can be called to release driver resources.
- **Release()** function
**Input parameter**:
**HdfDeviceObject**, an interface parameter exposed by the driver, contains the .hcs configuration.
**Return value**:
–
**Function description**:
Releases the memory and deletes the controller. This function assigns a value to the **Release()** API in the driver entry structure. If the HDF fails to call the **Init()** function to initialize the driver, the **Release()** function can be called to release driver resources.
cntlr=(structMmcCntlr*)obj->service;// Forcibly convert HdfDeviceObject to HdmiCntlr by using service. For details about the value assignment, see the Bind function.
cntlr = (struct MmcCntlr *)obj->service;// Forcibly convert HdfDeviceObject to HdmiCntlr by using service. For details about the value assignment, see the Bind() function.
...
HimciDeleteHost((struct HimciAdapterHost *)cntlr->priv);// Memory release function customized by the vendor. A forced conversion from HdmiCntlr to HimciAdapterHost is involved in the process.
}
```
> All forced conversion operations for obtaining the corresponding object can be successful only when the **Init** function has the corresponding value assignment operations.
> All forced conversion operations for obtaining the corresponding object can be successful only when the **Init()** function has the corresponding value assignment operations.
