Overlay in DSS

The display interface sub system has three planes to overlay with, two video planes and a graphics plane over a solid color background. This being said, to overlay 5 separate images there would need to be some software rendering being done before passing the frames to the DSS. This can certainly be done in software, though there are many options in software for doing this from a custom solution to existing Linux GUI tools like Qt.

Hi Thompson.

Thankyou so much for  the suggestions.

I am new to this field and I shall try this one with OMAP35x EVM.
Meanwhile could you please tell me what would be speed if I go for a software overlay,
and how the software overlayed data is transfered to the DSS.
I need to display the data through LCD(VGA) with more than 30fs.
And also is it possible to store this ovelay data to an external memory
say a flash memory directly from the DSS.

Regards...

Prad said:

Meanwhile could you please tell me what would be speed if I go for a software overlay,

This depends a lot on your software stack, and how efficient it is at mixing the images together, as well as the size of your display and of your images, and what other CPU loading tasks you have going on outside of the overlay. Performing overlay can be CPU intensive, but is certainly possible on the OMAP3.

Prad said:

and how the software overlayed data is transfered to the DSS.

The software overlayed data is simply passed to the display driver which manages the DSS hardware itself, it is mostly the passing of a pointer to a frame buffer.

Prad said:

And also is it possible to store this ovelay data to an external memory
say a flash memory directly from the DSS.

The frame buffers are almost certainly stored in external memory, particularly DDR, as internal memory is not large enough to hold the buffers due to their size. You could store images into flash however the DSS is only capible of reading directly from memory mapped devices such as internal memory, external DDR or asynchronous memory, the only practical place for storage of the frame buffers is DDR. Typically NAND is used as external flash on these devices, and since NAND requires a software layer to read from the DSS cannot read from it directly, so to leverage frame buffers stored in NAND the buffer would have to be read out to DDR in software and than passed to the DSS driver to display.

I am sorry I didn't mean the intermediate data,I shall use SDRAM as the memory frame buffer. What I wanted to ask was, storing the final output from DSS (i.e hardware ovelay data) to a flash memory. Is there any way to do this when the LCD display is suspended for a while. and aslo is it possible to read out this data(from flash) through USB interface in JPEG format.

Prad said:

What I wanted to ask was, storing the final output from DSS (i.e hardware ovelay data) to a flash memory. Is there any way to do this when the LCD display is suspended for a while.

Unfortunately this is not possible with the display sub system, the output can only go to the display itself, it is not routed back to memory. In this case the entire overlay operation would have to be done in software

Prad said:

and aslo is it possible to read out this data(from flash) through USB interface in JPEG format.

It is possible to read JPEG images stored in flash through USB, you would have to actually compress the image in JPEG using a JPEG codec however.

I am trying to understand about RFBI interface,

the reference manual (SPRUFA4B) "1.4.6 RFBI Functionalities" says that,
The RFBI module can capture the output pixel from the display controller and
send the data to the RFB in the LCD panel.

may be a wrong guess,
is it possible to use this to transfer data to flash memory.

are there any devices other than OMAP which has such fuctionality

Prad said:

is it possible to use this to transfer data to flash memory.

I suppose this could be possible, though you would probably need a CPLD/FPGA to do some adaption to your particular flash, and you would also have to have another interface to the flash (i.e. mux with the GPMC) so that you could read the data back out again as RFBI is a one way interface. This is definately not something that is out of the box or intended functionality though anything is possible with enough external logic.

Hi Thompson,

I am thinking about one more way to store the overlay data into flash memory,
say if I feedback the output from DSS back to the VPSS so that the data is transfered
to the DRAM and later to the Flash through DMA.
please let me your your opinion and any drawback with this procedure.

Thankyou and regards.

Prad said:

I am thinking about one more way to store the overlay data into flash memory,
say if I feedback the output from DSS back to the VPSS so that the data is transfered
to the DRAM and later to the Flash through DMA.
please let me your your opinion and any drawback with this procedure.

This is certainly a way to go, assuming you are not using the front end already for capturing video you could connect the display port to the capture port externally. The main drawback would be that your capture interface is used up by the process.