LCD Display shifted left

We have a custom LCD board with a Beaglebone and Angstrom 3.2 branch.

The LCD display is shifted to the left, with the missing portion displayed on the right. I’ve tried all sorts of timing changes to “da8xx-fb.c” and “board-am335cevm.c” using numbers from Vesa Coordinated Timing spreadsheet and elsewhere but it doesn’t seem to fix it, permanently. Sometimes its OK when I boot but when I reboot, its offset again.

How do I go about setting up the timing correctly? What is the reason for the offset?


Here’s what I’ve added to “da8xx-fb.c”:-

[6] = {
.name = “AUO-G121XN01”,
.width = 1024,
.height = 768,
.hfp = 24, //48, //80, //15, //48,
.hbp = 60, //80, //80, //15, //80,
.hsw = 136, //176, //32, //160, //160, //30, //32,
.vfp = 3, //3, //9, //3,
.vbp = 29, //15, //9, //15,
.vsw = 6, //4, //22, //20, //4,
.pxl_clk = 65000000,
.invert_pxl_clk = 0,

and this to “board-am335cevm.c”:-

// we are being stupid and setting pixclock from here instead of da8xx-fb.c
if (conf_disp_pll(130000000)) {
pr_info(“Failed to set pixclock to 130000000, not attempting to”
“register LCD cape\n”);


the stock angstrom build includes a program called fb-test. this allows you to identify the issues with the display. you will need make some calculations based on the display datasheet to determine the best front porch, back porch and sync width for both the horizontal and vertical syncs. for an introduction in debugging lcd and display interfaces, you can view slides and videos here:

Dave Anders

Thanks David.

I’ve downloaded the latest fb-test and compiled it. I’m not sure what the parameters should be.

gets the response…

fb-test 1.0.0 (tablet_rosa) fb res 1024x768 virtual 1024x2304, line_len 2048 dim 0mm x 0mm assert(common.c:62): : Invalid argument

I tried the parameters all the ways I could think of and got the same result.
./fb-test -f:0 -p:0

./fb-test -f0 -p0

and so on.

What is the correct command usage?