Forum Post: LCD Controller timing issue

Hello,

Our AM335x Beagle Bone Black board has a New Haven 7" TFT Display attached to it via a custom designed adapter similar to a cape. We're running Android and while Addroid will boot and display the Android logo on the screen, the image on the screen paints very slow and rolls. The image on the screen is stable, it's the painting of the image that appears to happen very slowly. I made some control signal timing measurements at the P8 connector and they are listed below.

P8-Pin 28    PCLK  period=8.6us, DC 1/99        should be 33.33nS    258x
P8-Pin 27    VSYNC period=4.5s (Seconds!)     should be 16.24ms    277x
P8-Pin 29    HSYNC period=8.5ms,                  should be 2.7uS      3148x
 
The numbers in the far right column are how far off the measurements are, for example PCLK is off by 258 times, it is actually 116.279KHz, not 30MHz. So it looks like a clocking issue to me, everything we measured is way off.

I dumped the register values in the LCD controller to see how the controller was configured and everything looked OK to me.

LCD Registers
[    1.453979] PID Reg 0x4830E000 : 0x4F201000
[    1.460357] CTRL Reg 0x4830E004 : 0x00000101
[    1.465270] LIDD_CTRL Reg 0x4830E00C : 0x00000000
[    1.470642] LIDD_CS0_CONF Reg 0x4830E010 : 0x00440044
[    1.476379] LIDD_CS0_ADDR Reg 0x4830E014 : 0x00000000
[    1.482116] LIDD_CS0_DATA Reg 0x4830E018 : 0x00000000
[    1.487854] LIDD_CS1_CONF Reg 0x4830E01C : 0x00440044
[    1.493621] LIDD_CS1_ADDR Reg 0x4830E020 : 0x00000000
[    1.499359] LIDD_CS1_DATA Reg 0x4830E024 : 0x00000000
[    1.505096] RASTER_CTRL Reg 0x4830E028 : 0x00000080
[    1.510650] RASTER_TIMING_0 Reg 0x4830E02C : 0x5828C310
[    1.516571] RASTER_TIMING_1 Reg 0x4830E030 : 0x200D0DDF
[    1.522491] RASTER_TIMING_2 Reg 0x4830E034 : 0x0230FF00
[    1.528411] RASTER_SUBPANEL Reg 0x4830E038 : 0x00000000
[    1.534332] RASTER_SUBPANEL2 Reg 0x4830E03C : 0x00000000

The only suspicious thing I found was the lcden bit in the RASTER_CTRL register was set to 0: LCD Controller disabled. That doesn’t make sense but I discovered it was set later in the code so I think that's OK.

First dump:
RASTER_CTRL Reg 0x4830E028 : 0x00000080

Later:
RASTER_CTRL Reg 0x4830E028 : 0x00000081

Any ideas how to resolve this issue are greatly appreciated.

Thanks,
john