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Unstable HD output on iMX6 Quad Plus Board

Question asked by Tony Bryant on Aug 30, 2019
Latest reply on Sep 12, 2019 by Tony Bryant

Have upgraded our iMX6 based product from Quad to QuadPlus:

 

- Everything works, BUT video output is unstable (i.e. flicks to all black randomly) at high resolutions, e.g. 1920x1080

- At 1024x768, output is 100% stable.

- Both Parallel RGB and HDMI outputs are affected identically

- Reducing pixclk down to 120MHz (from stock 138MHz) improves the situation a bit, but does not fix it.

- memtester is rock solid, as is every other type of software I have tried, including heavy multithreaded OpenCV ML stuff.

- Tried upping and lowering ARM/SOC & 2.5V supplies (via the standard PF0100 PMIC), without any change.

- Changing to LDO bypass mode doesn't make it better or worse

- Adding extra bypassing to SOC_CAP didn't help at all.

- Scoping all power rails shows clean and in-spec voltages.

- Adding extra bypassing to SOC_CAP didn't help at all.

- Loading up the system up, with either a memory tester or an OpenGL app, makes it

worse,  leading me to suspect memory bandwidth issue.  Raw CPU load that uses no memory doesn't affect the output.

- memtester seems to run at a slightly greater speed than the Quad boards, indicating greater memory bandwidth is available on the QuadPlus boards.

- AXI priorities in NoC and the GPR regs seem to be set up sensibly.

- Linux 4.9.128  Uboot 2018.07-32726, both derived from Boundaries Devices's Git.

- 64bit 1G DDR3 memory

- No kernel message during flicker events, though these messages are in the log:

 

imx-ipuv3 2400000.ipu: IPU Warning - IPU_INT_STAT_10 = 0x00080000
imx-ipuv3 2400000.ipu: IPU Warning - IPU_INT_STAT_5 = 0x08800000

 

Have I missed something important? 

 

I'm not sure if it's HW, or an IPU datapath setup issue, or something else?  I'm fishing for ideas for avenues to pursue at this point...

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