Basic Concepts

VI device/pipe/channel
- VI DEV
  The VI device supports multiple timing inputs and parses the timings.
- VI PIPE
  - Physical VI pipe
    The VI pipe is bound to the back end of the VI device. It is responsible for the ISP_FE and ISP_BE of the image algorithm processing after device parsing. It performs pipeline processing on the image data, and outputs YUV images to the channel.
  - Virtual VI pipe
    The virtual pipe is not bound to any device. It reprocesses the data transmitted from other modules or users. It does not support ISP_FE in the pipe and starts from ISP_BE in the pipe.
- VI CHN
  - Physical VI channel PHY_CHN
    The physical channel implements algorithm processing such as DIS and LDC using different hardware acceleration units, and outputs the processed data to the buffer. The following figure shows the functional block diagram of the channel.
    
    After the DIS and LDC functions are enabled, when hi_mpi_vi_set_chn_attr is called, an extra VB is allocated for each function. That is, the depth of the channel attribute needs to be increased by 1.
  - Extended VI channel EXT_CHN
    It is not supported by the current version.
Binding relationship
To transmit the video streams of the front-end camera module to the VI module through the MIPI for processing, the binding relationship between the device and the MIPI device must be met on the board-level connection of the Ascend AI Processor. Besides, as the flexible scheduling and orchestration on the software side must be ensured, you can adjust the binding relationship between the device and pipe.
- Binding relationship between the DEV and MIPI device
  The binding relationship between the VI device and the MIPI RX/SLVS-EC device is fixed and cannot be configured. The following table lists the mappings:
  
  Table 1 Binding relationship between the VI device and the MIPI RX/SLVS-EC interface
  VI DEV
  
  MIPI RX
  
  SLVS-EC
  
  0
  
  0
  
  0
  
  1
  
  1
  
  1
  
  2
  
  2
  
  X
  
  3
  
  3
  
  X
- The binding relationship between a device and a pipe is as follows:
  - Each pipe can be bound to any device by calling hi_mpi_vi_set_dev_bind_pipe. The pipe must be bound before being created by calling hi_mpi_vi_create_pipe. The binding relationship cannot be dynamically modified.
  - In linear mode (non-WDR mode), one device requires only one physical pipe. In WDR mode, one device requires multiple physical pipes, and only the channel of the first physical pipe bound to the device has data output. For example, in 2-to-1 WDR mode, pipe 0 and pipe 1 should be bound to the same device Dev0. Only the channel of pipe 0 outputs data.
LDC
Some low-end lenses are prone to image distortion. The images of these lenses need to be corrected based on the distortion degree.
DIS
The DIS module compares the current image with the previous two frames, calculates the jitter offset vectors of the current image in each axis using multiple degrees of freedom (DOF) DIS algorithms, and corrects the current image based on the jitter offset vectors. In this way, the DIS effect is achieved.
Low delay
After a specified number of lines of an image are written to the DDR, the VI module reports an interrupt and sends the image to the back-end module for processing. In this way, the delay is reduced, and the hardware mechanism ensures that the image is written first and then read so that no image reading error occurs. 3DNR, DIS, and LDC modules are connected to the ISP_BE and support the low-delay function.
Slave mode
Some sensors need to work in slave mode. In this case, the information about horizontal/vertical synchronization exposure synchronization needs to be provided externally, requiring the VI slave mode module. Determine the slave mode module to be used based on the sensor pin connection and the following table. Select the corresponding physical pipe ID to create a physical pipe or there will be no data.

Table 2 Mapping between slave modes and pipes
Slave Mode No.

Number of Connectable Sensors

Pin Name

Advised Pipe ID

0

2

SENSOR_VS0

SENSOR_HS0

0, 1

1

2

SENSOR_VS1

SENSOR_HS1

2, 3

**Table 1** Binding relationship between the VI device and the MIPI RX/SLVS-EC interface
VI DEV	MIPI RX	SLVS-EC
0	0	0
1	1	1
2	2	X
3	3	X

**Table 2** Mapping between slave modes and pipes
Slave Mode No.	Number of Connectable Sensors	Pin Name	Advised Pipe ID
0	2	SENSOR_VS0 SENSOR_HS0	0, 1
1	2	SENSOR_VS1 SENSOR_HS1	2, 3

The acronyms and abbreviations related to the VI function are as follows:

**Table 3** Acronyms and abbreviations
Acronyms and Abbreviations	Full Name	Description
VI	Video Input	Video input
WDR	Wide Dynamic Range	Wide dynamic range (WDR)
BE	Backend	FPN and the subsequent part in the ISP pipeline
FE	Frontend	The part before the FPN algorithm in the ISP pipeline
DIS	Digital Image Stabilization	Digital image stabilization
GME	Global Motion Estimation	Global motion estimation
GYRO	Gyroscope	Gyro
LDC	Lens Distortion Correction	Lens distortion correction
MIPI	Mobile Industry Processor Interface	Mobile industry processor interface
LVDS	Low-Voltage Differential Signal	Low-voltage differential signal
HISPI	High-Speed Serial Pixel Interface	High-speed serial pixel interface
SLVS-EC	Scalable Low-Voltage Signaling interface with an Embedded Clock	Scalable low-voltage signaling interface with an embedded clock
IPC	IP camera	Network camera
DV	Digital Visual	Digital video recording
PMF	Perspective Mapping Function	Perspective mapping function
MPP	Media Processing Platform	Media processing platform
ISP	Image Signal Processor	Image signal processing
Gyro DIS	Gyroscope Digital Image Stabilization	Gyroscope digital image stabilization

Parent topic: VI