Beadaframe: Display blanks out - PWM to backlight fails

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MrPec
Posts: 31
Joined: Mon Jan 02, 2012 11:39 pm

Beadaframe: Display blanks out - PWM to backlight fails

Post by MrPec » Wed Aug 08, 2012 5:13 am

Hi guys,

we have an issue with the beadaframe on some devices. Suddenly, the displays blanks out.
We tracked the issue down and we found out that there's no more PWM coming from your Altera going to the dc-dc regulator on the display's backside.

Everything else works fine, the device is still running and the display itself also works (after rebooting, the latest content is visible for a short time).
It's just the backlight thats switched off. The PWM is static at around 0.6V, and therefore the PWM out of the regulator is only 5V, while it's 9.3V if it's running fine.

Is there anything we can do about it? It looks like the FPGA is resetting, and therefore there are no values for the pwm...

Thanks for your help!

Best regards,

Alex

esky-sh
Posts: 1435
Joined: Sat Dec 20, 2008 4:21 am

Re: Beadaframe: Display blanks out - PWM to backlight fails

Post by esky-sh » Wed Aug 08, 2012 6:08 pm

'echo 50 > /sys/class/backlight/pwm-beada/brightness'
'echo 100 > /sys/class/backlight/pwm-beada/brightness'
to manually control the brightness. Please monitor serial logs to find if any failure from i2c backlight drivers.

esky-sh
Posts: 1435
Joined: Sat Dec 20, 2008 4:21 am

Re: Beadaframe: Display blanks out - PWM to backlight fails

Post by esky-sh » Wed Aug 08, 2012 10:13 pm

Another method to verify this issue:
Do not power cycle the board when failure happened, just restart your software to check if backlight recover to normal.

MrPec
Posts: 31
Joined: Mon Jan 02, 2012 11:39 pm

Re: Beadaframe: Display blanks out - PWM to backlight fails

Post by MrPec » Wed Aug 08, 2012 10:54 pm

Hi,

we already tried both methods. If we reboot the board (warm start, typing reboot in the console), the pwm is back and the board works fine.
Just writing other values to the pwm-beada does not work.
It seems that the FPGA resets itself, and that some initial values are missing after that.

There are no errors reported on the console, and there are also no errors shown in dmesg.
Soemtimes there's an error regarding the touchscreen:

[ 279.088531] tsc-beada 2-0052: i2c io error: -121

But i've only seen that once, and in my opinion it also indicates that there was a power failure on your extension board, which may lead to the FPGA resetting...

Best regards,

Alex

esky-sh
Posts: 1435
Joined: Sat Dec 20, 2008 4:21 am

Re: Beadaframe: Display blanks out - PWM to backlight fails

Post by esky-sh » Thu Aug 09, 2012 12:14 am

yes you are right.

the backlight control pin is muxed to 2 different modules inside CPLD, one is PWM and another is GPIO.
the GPIO module is default in input mode and there is a pull down resistor R30 on NHBC07 board. so the backlight will be off when the CPLD get reset.

every time pwm backlight driver get probed, it will write a control bit to CPLD to let the pin exposed as PWM output.
this may explain why backlight output recovered whenever the driver get re-probed.

You may double check with it, by pulling up the PWM output pin(remove R30).
pwm_mux.jpg
pwm_mux.jpg (136.34 KiB) Viewed 7426 times
MrPec wrote:Hi,

we already tried both methods. If we reboot the board (warm start, typing reboot in the console), the pwm is back and the board works fine.
Just writing other values to the pwm-beada does not work.
It seems that the FPGA resets itself, and that some initial values are missing after that.

There are no errors reported on the console, and there are also no errors shown in dmesg.
Soemtimes there's an error regarding the touchscreen:

[ 279.088531] tsc-beada 2-0052: i2c io error: -121

But i've only seen that once, and in my opinion it also indicates that there was a power failure on your extension board, which may lead to the FPGA resetting...

Best regards,

Alex

MrPec
Posts: 31
Joined: Mon Jan 02, 2012 11:39 pm

Re: Beadaframe: Display blanks out - PWM to backlight fails

Post by MrPec » Wed Aug 15, 2012 4:41 am

Thank you, I'm going to check that....

MrPec
Posts: 31
Joined: Mon Jan 02, 2012 11:39 pm

Re: Beadaframe: Display blanks out - PWM to backlight fails

Post by MrPec » Fri Aug 17, 2012 6:26 am

After removing that R30, the boards works as before. So, the CPLD should now work without initialization?

MrPec
Posts: 31
Joined: Mon Jan 02, 2012 11:39 pm

Re: Beadaframe: Display blanks out - PWM to backlight fails

Post by MrPec » Fri Aug 17, 2012 6:51 am

Ok, I just forced a reset of the CPLD by pulling the 3V3 low for a short period ;)
Unfortunatley, there's no pwm after that, I have to restart the board to get it back working...

Any ideas?

esky-sh
Posts: 1435
Joined: Sat Dec 20, 2008 4:21 am

Re: Beadaframe: Display blanks out - PWM to backlight fails

Post by esky-sh » Fri Aug 17, 2012 8:17 pm

MrPec wrote:Ok, I just forced a reset of the CPLD by pulling the 3V3 low for a short period ;)
Unfortunatley, there's no pwm after that, I have to restart the board to get it back working...

Any ideas?
I think there should be 3 possible solutions:
1. Fasten your connections between Pandaboard and NBD01 board.
The power failure should caused by connection issue between those 2 boards.
2. Modify software drivers to let backlight module update control bit on every visit.
3. Modify cpld firmware to force GPIO pin output HIGH from reset.

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