AM335x LCD Controller settings

paddu1

Hi,

We have a problem with the AM335x LCD controller.

We are using AM335x LCD controller in Raster mode.
Sometimes there are FIFO underflow interrupts and we are not able to update/redisplay
the image through resetting the interrupt flag.
Please let us know what could be done when such error occurs.

In this application we need to stop the display and replay it sometimes.
So we are trying to disable and enable the display whenever required through
LCDEN bit,
but once it is disabled when we try to enable the display,
FIFO underflow & the Frame Done interrupts seems to be ON and we are not
able to enable the display.
We would like to know if there is any procedure or register settings in such case.

Regards.
Paddu.

over 13 years ago

0 Prakash PM over 13 years ago

TI__Intellectual 1275 points

Hi,

Are you using Linux? You can refer to Linux driver:http://arago-project.org/git/projects/?p=linux-am33x.git;a=blob;f=drivers/video/da8xx-fb.c;h=2e69278dd3fd00fe70efda10f1aa74d446467e53;hb=1b21543aae1844cd2b59bb0f257d6f62c38f39f9

Please make sure that you have configured burst_size and DMA FIFO threshold (LCDDMA_CTRL register) to maximum.

Also you can recover from underflow hits by setting auto_uflow_restart:1 in control register.

Thanks,

Prakash

0 paddu1 over 13 years ago in reply to Prakash PM

Expert 1195 points

Hi Prakash,

Thank you.
With you suggestions we were able to reduce DMA FIFO underflow,
but were not able to reduce it completely.

Could you please let us know if there is any other things we
could do in order to completely control the FIFO underflow error.

We appreciate your kind suggestion.

Best Regards
Paddu.

0 Prakash PM over 13 years ago in reply to paddu1

TI__Intellectual 1275 points

Hi Paddu,

Underflow errors are observed because of slow DDR, could you try increasing DDR refresh rate?

Also when you enable auto_uflow_restart, make sure to not enable and handle underflow error.

Thanks,

Prakash

0 paddu1 over 12 years ago in reply to Prakash PM

Expert 1195 points

Hello Prakash,

Thank you so much for the suggestions.
And I am extremely sorry for the delay.

Regarding "increasing DDR refresh rate"
if possible could you please let me know how could we increase the DDR3 refresh rate.
The AM335x TRM mentions about "reg_refresh_rate" bit in SDRAM_REF_CTRL Register,
should we increase the value of this bit?

Best Regards.
Paddu.

0 paddu1 over 12 years ago in reply to paddu1

Expert 1195 points

Hello Prakash,

Regarding the SDRAM refresh control register（SDRAM_REF_CTRL)
using CCS we found that the value is set to "0x0000093b", so the REG_REFRESH_RATE = 0x93B = 7.8us.
And the DDR3 "MT41J128M16HA" datasheet mentions "average refresh rate of 7.8125μs"

Regards.
Paddu

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AM335x LCD Controller settings