Did you try one of Newhaven's existing images to see if the hardware is working properly? The NewHaven's forum may also be a good place to ask this.
Unfortunately I don't have the same cape, but if you issue a menuconfig to re-configure u-boot, one of the sections is related to Graphics support - in my distro it is disabled by default, but you could try to enable it, rebuild u-boot and see if it works ok.
From the u-boot source directory you can issue a make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- menuconfig
The New Haven Display user guide software compatibility section says that this display cape is compatible with Ubuntu 14.04. Are you willing to use Ubuntu instead of the default LXQT?
When I clicked on the link in the user guide, it took me to dropbox for the Ubuntu version that they recommend. I don’t have this cape to try it, but that may make it simple for you to use your display cape and BBB computer. Ubuntu14.04 was likely the version available when they developed this display cape.
The other option listed in the user guide is Android, but Ubuntu is much more similar to Debian LXQT.
I have a 4D systems Cape (7"). I too have issues with the latest debian(9.4) image. I have been able to get my cape to work with "debian 9.3" but I have to have the HDMI plugged into an external monitor. If I plug the HDMI into a monitor (monitor on of off) the LCD cape back light illuminates and the desktop displays on the LCD cape.
When I have both the cape and HDMI cable plugged in, both displays function as desired with the exception of the resolution. I set uEnv.txt to run at 640x480@60 which is why the right side of the cape has a black bar (display "cut off").
Maybe you can try to get an HDMI cable and external monitor and at least prove that the display works and that it is just a configuration issue as I have.
I am still trying to wrap my head around how linux handles a few display items.
I have been struggling with two issues all weekend:
1) why wont the debian 9.4 work with the 7" display for 4D systems (I have the one with headers which enable the beagle bone black to be directly mounted on the LCD panel)
2) why do I need the HDMI cable plugged in for the system to recognize that display/s are attached.
My assumptions for each topic:
1) for the versions 9.6 to 9.3, something changed in the device overlay and/or hardware for the 4D systems cape. I notice 4D systems now has a new model out of the 7" LCD.
2) I think the EDID might have something to do with why the cape will not work without an HDMI cable plugged into the Beaglebone black but this is just a theory.
The picture below is debian 9.3 w/ LXDE desktop version, 4D systems 7" LCD cape with an external monitor. (resolution is 640x480 @ 60)
Dear All. I've recently bougth a BBB and a touch display cape from NHD-7.0CTP-CAPE-N NHD-7.0CTP-CAPE-N [165mm x 119.21mm] - $93.00 : Newhaven Display International, Inc., High Quality Sta…
There is no way to make it works with the latest debian (9.4) Stretch LXQT image provided by beagleboard.org. It seems to be an U-boot issue but for Debian newcomers it is hard to manage this stuff..
We would appreciate suggestions.