Backlight BL_ON signal at power-on doesn't wait for stable pixel data

Technical Support
, ,
1

Shouldn’t the BL_ON wait until pixel data and clock signals are stable, before going active?
It appears to go active immediately at power on, resulting in a brief (100-200ms) flash of white on my LCD before splash screen is displayed.

Just as on Colibri Ev Board 3.2B, I wired BL_ON to drive the PWRDWN pin on the LVDS driver, as well as the enable pin on my backlight driver.
Same components as your ref design.

I use the default BL_ON pin SODIMM-71.

Colibri VF61 1.2A,
CE6 image 1.5

Bootloader is from same package
(how can I tell bootloader version after it’s installed???)

2

@ebbe,

We are looking into it. Could you please wait for sometime. We will get back you soon.

3

If this is problematic to detect in the driver, a configurable delay after power-on would be a huge help, as I think the time for valid data to appear is pretty constant.

Ebbe

4

Thanks Andy, I added a pulldown for good measure. I look forward to that feature being implemented.

I’d like to mark the question as answered, but didn’t see the option.

Thanks for your help.
Ebbe

5

We created a feature request and will discuss next week, whether we can implement this option into the bootloader.

Please be aware that there is still a time between power-up and executing the bootloader code, when we don’t have software control over the backlight pin. It is probably floating and should be pulled to inactive state on your carrier board.

6

This option can be somehow useful;

I see that for “Display On/Off Gpio”, bootloader already has a “Display On Delay (ms)” setting (ss.dispondelay).

It’s only an idea, but mabe a ss.blondelay parameter could be a solution.

7

Dear @ebbe
We decided to implement a configurable delay for the BL_ON signal, as we have done it already on other platforms. We didn’t decide on a schedule yet.
Regards, Andy

8

That’s great news. Kudos to your dev team!

Thank you.

9

Dear Ebbe,

We implemented this feature and will be released in next version.

You can use early release to test it.

https://share.toradex.com/0x3vr0lwjafi3jb

You can use ss.dispondelay parameter to delay backlight and display on pins. Setting is in milliseconds.

Have a nice day.