Enabling ADC disables HDMI?

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Enabling ADC disables HDMI?

Postby ryansturmer » Tue Feb 05, 2019 4:23 pm

I am trying to enable the ADC on my beaglebone black and am wading through the whole device tree overlay thing, which has apparently changed fairly recently (with the deprecation of capemgr, etc)


I followed the advice in the post above, replacing the PRU device tree blob, with the BB-ADC one, and my ADC works perfectly now.

Unfortunately, my HDMI has stopped working - is there a way I can bring it back?

This is my boot.txt. The commented out lines are the ones that activate the ADC. If I remove them and reboot, my HDMI comes back:
Code: Select all
# After modifying, run ./mkscr

if test -n ${distro_bootpart}; then setenv bootpart ${distro_bootpart}; else setenv bootpart 1; fi
part uuid ${devtype} ${devnum}:${bootpart} uuid

setenv bootargs "console=tty0 console=${console} root=PARTUUID=${uuid} rw rootwait"

if load ${devtype} ${devnum}:${bootpart} ${kernel_addr_r} /boot/zImage; then
  gpio set 54
  echo fdt: ${fdtfile}
  if load ${devtype} ${devnum}:${bootpart} ${fdt_addr_r} /boot/dtbs/${fdtfile}; then
#    fdt addr ${fdt_addr_r}
#    load ${devtype} ${devnum}:${bootpart} 0x88060000 /lib/firmware/BB-ADC-00A0.dtbo
#    fdt resize ${filesize}
#    fdt apply 0x88060000
    gpio set 55
    if load ${devtype} ${devnum}:${bootpart} ${ramdisk_addr_r} /boot/initramfs-linux.img; then
      gpio set 56
      bootz ${kernel_addr_r} ${ramdisk_addr_r}:${filesize} ${fdt_addr_r};
      gpio set 56
      bootz ${kernel_addr_r} - ${fdt_addr_r};

Posts: 6
Joined: Sat Jun 14, 2014 6:06 pm

Re: Enabling ADC disables HDMI?

Postby summers » Wed Feb 06, 2019 11:21 am

Well as you are just applying the ADC overlay, if its been done properly it will just grab the pins it needs for the ADC.

The TI am355x greatness is that nearly all of its pins can be programmed between something 6 different modes, it what means that processor has such a huge number of interfaces.

That said, the problem is what if the pins you use, are already allocated to another device, then you need to decide which you want to use.

Sure way to check, is look into the overlay to see what pins it is using, then check which pins are used from HDMI. That will point to if a way round, e.g. if it enables 2 ADC ports, does only one clash with hdmi? If so then you could use the other ADC, and keep the hdmi. Anyway need some research.

Also the beagle bone black specification/manual is excellent - reading that and you can see the pins as well, and which are shared ...
Posts: 926
Joined: Sat Sep 06, 2014 12:56 pm

Re: Enabling ADC disables HDMI?

Postby summers » Wed Feb 06, 2019 4:57 pm

Ok am confused now. the ADC is on P9 on pins 33-40; these are dedicated to the ADC so there shouldn't be any conflicts.

Its all the device tree ovelay access: https://github.com/beagleboard/bb.org-overlays/blob/master/src/arm/BB-ADC-00A0.dts

So I'm confused that hdmi stops working ....
Posts: 926
Joined: Sat Sep 06, 2014 12:56 pm

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