About dropout of VSYNC and HSYNC for LCD of i.MX25

[yuuki]

Dear all,

We connect an LCD panel to i.MX25.
(LCD:  688 x 600 / 24bpp / 44.3MHz)

We have the problem that a noise is over to LCD.
A white line and a black line are displayed.

We checked a waveform of VSYNC and HSYNC.
We found the waveform of VSYNC and HSYNC dropouted.

[VSYNC]   Blue: VSYNC / Aqua: DE

[HSYNC]  Blue: HSYNC / Aqua: OE / Red: LD

When dropout of VSYNC and HSYNC occurred, it seems that underrun error occurs.
LISR=0x0000000B

Can the underrun error become the cause that dropout of VSYNC and HSYNC occurs?

If it is Yes,
May I have advice about a method avoiding Underrun error?

Best Regards,
Yuuki

[igorpadykov]

Hi Yuuki

in general yes, this may be caused by underruns,

you can test that reducing lcd framerate.

For avoiding underruns one can try to place lcd buffer

in iRAM.

Best regards

igor

-----------------------------------------------------------------------------------------------------------------------

Note: If this post answers your question, please click the Correct Answer button. Thank you!

-----------------------------------------------------------------------------------------------------------------------

[yuuki]

Dear Igor-san,

Thank you for your support.

Would you tell me the method to put LCD Buffer in iRAM?

We want to try it.

Best Regards,

Yuuki

[igorpadykov]

Hi Yuuki

one can look at example of iRAM usage from usb driver,

check attached document p.148 IRAM support

and make similar modifications in LCD driver.

Best regards

igor

[yuuki]

Dear Igor-san,

Thank you for your support.

Can use of iRAM solve a problem?

iRAM size is 128KByte.
However, The size required for LCD Buffer is about 1.2MByte.
  686 x 600 x 3Byte = 1234800 Byte (about 1.2MByte)

I think that size of iRAM is not enough.

Best Regards,
Yuuki

[igorpadykov]

Hi Yuuki

you are right, only small size LCD can be used with iRAM

Best regards

igor

[yuuki]

Daer Igor-san,

Thank you for your response.

I think that iRAM use does not become workaround for this problem because iRAM size is very small.

Is there the method to avoid this problem, other than iRAM use?

May I have advice?

Best Regards,
Yuuki

[igorpadykov]

Hi Yuuki

I think onlt way to decrease bus load: decrease LCD frame rate,

bits/per pixel or size

Best regards

igor