DM642 EVM Video DAC - Video encoder to display video

Library

Description

In the project generated from a model, this block provides the code to gather video from another block in the model, and direct the video stream to the video output port on the board.

You should input unsigned 8-bit integers to the block in the specified mode.

Adding this block to a model enables code generated from your model to perform the following tasks:

Capture digital video data from the application on your DM642 EVM.
Buffer the captured video into frames for NTSC display — two fields per frame and 30 frames per second, or SVGA display — RGB24 color with noninterlaced frames.
Convert to analog video.
Output the converted analog video to the EVM Video Out ports.

Unlike the DM642 EVM Video ADC block, this DAC block does not convert the video between formats. Nor does this block inherit any settings from the DM642 EVM Video ADC block, as some of the other C6000 DAC blocks do.

The Mode option specifies both the video format the block accepts and the format the block outputs to the video output ports on the EVM.

To be able to be displayed, images that you send to the block should be equal to or smaller than the target display size. If the input images are smaller than the target display size, the block pads the image by adding zeros to the image.

When you add this block to your Simulink model, it has no affect on your simulation — it outputs a string of zeros. In code generation, the block creates the device code needed to buffer, convert, and send video to the output port on the EVM.

Note The DM642EVM board provides both composite and S-video connectors for output. However, these are driven simultaneously, so you do not need to specify which one is to be used.

Memory Use

This block allocates video capture buffers on the system heap, using a TI driver that allocates three frame buffers on the heap for continuous video capture. To use the block you must create a heap in external memory on the target with the label EXTERNALHEAP. If you do not create the heap, either using the default values in the DM642 Target Preferences block or setting your own values. Target Support Package software returns an error.

Use Create heap and Heap size and set the heap size in the DM642EVM Target Preferences block to configure the heap. Select Define label and name the heap EXTERNALHEAP in Heap label.

The default settings for the target preferences create a heap with sufficient memory to handle the worst case memory allocation needs automatically. If you configure the heap without sufficient memory, you get a run-time error because the system cannot initialize the video driver.

Dialog Box

Mode

Specifies the video format for the block. The block then sends video in this format to the video output port on the EVM. The Mode parameter offers the following options:

Analog Output Mode	Description
`NTSC 720x480 YCbCr`	Analog output of video data in 720-by-480 pixels format with full color.
`NTSC 640x480 Y`	Analog video output in 640-by-480 pixels format with black and white only (luminance). No color data.
`SVGA 800x600 RGB24`	Full super VGA format 800-by-600 pixels with three color channels: 8-bit red, 8-bit green, and 8-bit blue data.
`PAL 720x570 YCbCr`	Analog output of video data in 720-by-570 pixels PAL format with full color.
`PAL 720 x 570 Y`	Analog output of video data in 720-by-570 pixels PAL format with black and white only (luminance). No color data.

Data order

With data order, you control the way the video decoder stores and outputs video data fields and frames of images. Choose one of these options from the list.

Row major — store video data in row major order. This is the default setting and matches most video data.
Column major — store video data in column major order. Simulink and MATLAB software use this format to store images and matrices.
DM642 EVM Video DAC blocks store the image data in row major format because most video display devices use a scanning order of left-to-right and top-to-bottom, favoring the rows.
MATLAB and Simulink software use column major ordering to store image and matrix data. Therefore, some of the Simulink blocks may not work correctly or as expected with the DM642 EVM Video DAC blocks.
To address this problem, the Video DAC blocks include an option Data order to let you select either row major or the column major storage formats. By default, these blocks use row major data format.
When the column major data ordering option is selected, the block performs an explicit transposition on the image data to map the data format from row major to column major order. To minimize the processor time spent on the transposition, the block uses optimized assembly routines to accomplish the image transposition.

Center Image

Directs the block to center the output image on the display. Centering the image requires some computation by the processor so there are small time and CPU cycles penalties for choosing this option. For that reason, Center image is cleared by default.

Another note of interest — some cameras pad their video output with zeros to ensure that the display does not cut off the image on one side, usually the left. Images that include such padding may appear to be off-center on the display. In fact, while the displayed image may not appear centered, the electronic image (the data that compose the displayed image plus the padding which you cannot see) is centered in the display area.

DM642 EVM Video DAC - Video encoder to display video

Library

Description

Memory Use

Dialog Box

See Also

Recommended Products