Q&A: Can i.MX6Solo LDB/LVDS & LCD Ports be active simultaneously

Document created by Yixing Kong Employee on Aug 16, 2013
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Q:

Some background; this instrument has one display connected to the LVDS output of the i.MX6Solo and the SVGA monitor is using the IPU port with an external Analog Devices ADV7125 DAC to actually drive the monitor (or projector).  From Tektronix:

 

We got our kernel logo to show up on an external SVGA monitor as well as on the internal LVDS display so we now at least know that the hardware is functional.

 

However, when our application starts running and writing to the fb0 (background) and fb1 (foreground/overlay) frame buffers, the external monitor (fb2 frame buffer) doesn't get updated.

 

We need to know how to get the same data going to the external monitor as goes to the internal LVDS display.  the external monitor is 800x600 and the internal is 800x480 so we'd further like those 480 lines to show up centered in the 600 line monitor.

 

We are also hoping that this can be down without having to write/DMA all of the data twice.

 

The answer given is SR #1122663812 was "If the customer is using Linux, fb2 should also be drawed by their application."  This was considered in adequate and Tek replied:

 

I would like to know if they are saying that the IPU absolutely cannot automatically do what we want and if not, why not?  I would like to have some detailed information to at least convince us that they've looked into this and it really isn't possible.

 

A:

In our Linux BSP we don't support such feature. And in android BSP it was already supported.


The customer must draw the fb2 by their application, ipu doesn't have the feature that combining the fb0 and overlay fb1, then resize it to fb2 automatically.

 

The customer application can drawing their UI into a memory, then use v4l2 output to draw this buffer to both fb0 and fb2, in this case, resizing will be implemented in V4l2 output driver with IPU hardware. And if the customer needs overlay on fb2, they must combine the two layer into memory with IPU task first, then using V4l2 output to render it to display fb2.

 

For how to use IPU task, the customer can reference to BSP unit test code: imx-test-1.1.0\test\mxc_ipudev_test

 

The summary: for dual display case, the fb0 and fb2 are just two framebuffer memory, they must be filled before rendering to display, on iMX6S/DL, only the fb0 has the hardware overlay (fb1); if the customer wants to show same contents on two displays in Linux, their application must draw the two framebuffers, but we had some hardware method to improve the performace, using GPU or IPU task.

 

In Android, the application will not draw frame buffer directly, it will use Android surface flinger middleware to draw, so this feature was implemnted in surface flinger; but in Linux, there is no such middleware, and application draws the framebuffer directly, so the application should handle it.

 

This document was generated from the following discussion: i.MX6Solo LDB/LVDS & LCD Ports Active Simultaneously

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