# Beaglebone Mender image doesn't enable PRUs

**URL:** <https://hub.mender.io/t/beaglebone-mender-image-doesnt-enable-prus/4218>\
**Category:** General Discussions\
**Created:** [October 22, 2021, 6:40am UTC](https://hub.mender.io/t/beaglebone-mender-image-doesnt-enable-prus/4218 "2021-10-22T06:40:15Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![azarubkin](https://avatars.discourse-cdn.com/v4/letter/a/8edcca/32.png) [@azarubkin](https://hub.mender.io/u/azarubkin)\
**Post date:** [October 22, 2021, 6:40am UTC](https://hub.mender.io/t/beaglebone-mender-image-doesnt-enable-prus/4218/1 "2021-10-22T06:40:15Z")

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I’ve noticed there are no entries corresponding to PRUs of the Beaglebone Black board when booting the image with Mender.  
There are some entries in `/boot/uEnv.txt` which configure PRUs like `disable_uboot_overlay_video=1` and

```auto
###pru_rproc (4.19.x-ti kernel)
uboot_overlay_pru=/lib/firmware/AM335X-PRU-RPROC-4-19-TI-00A0.dtbo

```

Since Mender doesn’t boot the kernel using U-Boot, I guess something should be put to `boot/efi/EFI/BOOT/grub.cfg` instead to load the dtbo file and disable the HDMI?

In other words, how do I enable PRUs in Mender image?

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<div class="post-metadata">

**Author:** ![kacf](https://yyz2.discourse-cdn.com/flex036/user_avatar/hub.mender.io/kacf/32/146_2.png) [@kacf](https://hub.mender.io/u/kacf)\
**Post date:** [October 22, 2021, 7:20am UTC](https://hub.mender.io/t/beaglebone-mender-image-doesnt-enable-prus/4218/2 "2021-10-22T07:20:18Z")

</div>

U-Boot is actually being used, but not to load the kernel. Instead U-Boot acts as a UEFI provider, where UEFI is a boot standard. The reason for doing it like this is so that we can use a standardized GRUB binary across all boards, instead of a specialized U-Boot binary.

U-Boot is the still the one which loads dtbs, so it can still be influenced. However, when using U-Boot as a UEFI provider, we execute the `distro_bootcmd` step, and I’m not sure if it takes `uEnv.txt` into account if there is a UEFI app (GRUB) present. It’s possible you will have to set this in the U-Boot environment instead, either by recompiling it or by manually modifying and saving the environment using the U-Boot prompt. Some experimentation is probably necessary here.