(newbie) PWM is missing in Debian 13.2 images

General Discussion
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1

Now that I can turn on/off GPIO pins and builtin LEDs in BBB, I would like to try PWM next. Online search says something about “config-pin”, “/dev/bone/pwm”, and “/sys/class/pwm”. But,

whereis config-pin
ls /dev/bone/pwm
ls /sys/class/pwm

all return empty in the latest Debian 13.2 images,

  • am335x-debian-13.2-base-v5.10-ti-armhf-2025-11-18-4gb.img.xz
  • am335x-debian-13.2-base-v6.12-armhf-2025-11-18-4gb.img.xz
  • am335x-debian-13.2-base-v6.17-armhf-2025-11-18-4gb.img.xz

How do I enable PWM in BBB?

Here is output of “beagle-version” for 6.17.9-bone17 kernel.

eeprom:[A335BNLT0A5A1913BBBK2768]
model:[TI_AM335x_BeagleBone_Black]
dogtag:[BeagleBoard.org Debian Trixie Base Image 2025-11-18]
bootloader:[eMMC-(default)]:[/dev/mmcblk1]:[U-Boot SPL 2022.04-gb4b56c73 (Oct 28 2025 - 17:45:28 +0000)]:[location: dd MBR]
UBOOT: Booted Device-Tree:[am335x-boneblack.dts]
kernel:[6.17.9-bone17]
/boot/uEnv.txt Settings:
pkg check: to individually upgrade run: [sudo apt install --only-upgrade <pkg>]
pkg:[bb-customizations]:[1.20250808.0-0~trixie+20250808]
pkg:[bb-usb-gadgets]:[1.20250523.1-0~trixie+20250527]
pkg:[bb-wl18xx-firmware]:[1.20230703.0-0~trixie+20240703]
pkg:[kmod]:[34.2-2bbbio1~trixie+20250522]
groups:[debian : debian adm kmem dialout cdrom floppy audio dip video plugdev users systemd-journal input render netdev i2c bluetooth gpio admin tisdk weston-launch]
cmdline:[console=ttyS0,115200n8 root=/dev/mmcblk1p3 ro rootfstype=ext4 rootwait fsck.repair=yes earlycon coherent_pool=1M net.ifnames=0 lpj=1990656 rng_core.default_quality=100]
dmesg | grep remote
[   17.349769] systemd[1]: Reached target remote-fs.target - Remote File Systems.
[   35.829970] remoteproc remoteproc0: wkup_m3 is available
[   35.975769] remoteproc remoteproc0: powering up wkup_m3
[   36.005453] remoteproc remoteproc0: Booting fw image am335x-pm-firmware.elf, size 217148
[   36.045623] remoteproc remoteproc0: remote processor wkup_m3 is now up
[   55.190740] remoteproc remoteproc1: 4a334000.pru is available
[   55.263798] remoteproc remoteproc2: 4a338000.pru is available
dmesg | grep pru
[   47.544963] Modules linked in: 8021q snd_soc_ti_udma garp stp snd_soc_ti_edma llc mrp snd_soc_ti_sdma cfg80211 iptable_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 iptable_mangle iptable_filter snd_soc_hdmi_codec snd_soc_core bluetooth ecdh_generic rfkill ti_am335x_adc snd_compress kfifo_buf zram industrialio snd_pcm_dmaengine snd_pcm snd_timer snd soundcore at24 wkup_m3_rproc evdev nfnetlink ip_tables x_tables pruss pm33xx wkup_m3_ipc uio_pdrv_genirq uio
[   55.190740] remoteproc remoteproc1: 4a334000.pru is available
[   55.263798] remoteproc remoteproc2: 4a338000.pru is available
dmesg | grep pinctrl-single
[    3.618521] pinctrl-single 44e10800.pinmux: 142 pins, size 568
dmesg | grep gpio-of-helper
dmesg | grep wlcore
lsusb
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
END
2

What you’ve found is old and outdated information.

Unfortunately, the Internet is very good at perpetuate and amplify exactly that.

What you want is device-tree overlays. They should already be installed on your Beagle,
somewhere under /usr/share/… (search for .dtso files).

3

Which pwm pins do you need? You’ll find a few pre built overlays under /boot/

4

You will need to add overlays to the boot uEnv.txt file. I have an example PWM class for the Beaglebone Black here:

This is a portion of my /boot/uEnv.txt file, note the “Additional custom capes” section and the pins assigned by the prebuilt overlays.

uname_r=6.12.49-bone36
#uuid=
#dtb=

###U-Boot Overlays###
###Documentation:
###Master Enable
enable_uboot_overlays=1

###Overide capes with eeprom
#uboot_overlay_addr0=.dtbo
#uboot_overlay_addr1=.dtbo
#uboot_overlay_addr2=.dtbo
#uboot_overlay_addr3=.dtbo

###Additional custom capes
uboot_overlay_addr4=/boot/dtbs/6.12.49-bone36/overlays/BB-EHRPWM1-P9_14-P9_16.dtbo
uboot_overlay_addr5=/boot/dtbs/6.12.49-bone36/overlays/BB-EHRPWM2-P8_13-P8_19.dtbo
#uboot_overlay_addr6=.dtbo
#uboot_overlay_addr7=.dtbo

###Custom Cape

5

Does anyone have a book to recommend for writing Device Trees for the Beaglebone boards. I have struggled for years for modifying the .dts files on the BBAI64. It seems to me that with every kernel change their is a shift towards re-configuring your own board. I started with Derek Mollys book with the original BBB years ago. I have purchased 2 books that have been of limited help. The problem is I simpily don’t speak the Device Tree Language and get lost quickly.

6

No reason to add the text.. ‘/boot/dtbs/6.12.49-bone36/overlays/’ that breaks kernel updates

7

What do you suggest. Yes it seems like everytime the kernel changes, my system breaks. Is their an alternative to adding the overlays, similar to the BBAI64?

8

u-boot knows where to look, remove the extra stuff..

uboot_overlay_addr4=BB-EHRPWM1-P9_14-P9_16.dtbo
uboot_overlay_addr5=BB-EHRPWM2-P8_13-P8_19.dtbo

Regards,

9

I got them from Cookbook, Chapter 3 and also from this Forum. Yes, they were all old.

Nothing under /usr/. But, I found something under /boot and /opt,

  • /boot/dtbs/6.17.9-bone17/BB-EHRPWM1-P9_14-P9_16.dtbo
  • /boot/dtbs/6.17.9-bone17/BB-EHRPWM2-P8_13-P8_19.dtbo
  • /opt/source/dtb-6.17.x/src/arm/overlays/BB-EHRPWM2-P8_13-P8_19.dtso
  • /opt/source/dtb-6.17.x/src/arm/overlays/BB-EHRPWM1-P9_14-P9_16.dtso

Curiously, nothing on “PWM0”, though.

10

Thanks I get it now.

11

Thank you. I got an external LED blinking. For now, pre-defined

  • PWM1 – P9_14 (a), P9_16 (b)
  • PWM2 – P8_19 (a), P8_13 (b)

are good enough.

What happened to “PWM0” (P9_31, P9_29)?

12

Added… Commits · beagleboard/BeagleBoard-DeviceTrees · GitHub

cd /opt/source/dtb-6.17.x/
git pull

Then build:

./build_n_install.sh

and you can give it a test.. make sure you have hdmi audio disabled..

Regards,

13

What am I doing wrong I removed the full path /boot/dtbs/6.12.49-bone36/overlays as suggested.

Getting at boot time error message:

uboot_overlays: unable to find [mmc 0:3 BB-EHRPWM1-P9_14-P9_16.dtbo]

14

have you done

sudo find / -name BB-EHRPWM1-P9_14-P9_16.dtbo

to verify that it exists in /boot/.

and uEnv.txt should only need (as RCN indicated above)

uboot_overlay_addr4=BB-EHRPWM1-P9_14-P9_16.dtbo

15

Yes, “PWM0” works too, now.

What you mean by “disabled”?

  • BBB is running headless, bare bone “out of box”. So, nothing is plugged into microHDMI port. And, I don’t have any “cape”.
  • And, I haven’t done anything “audio” related. I wouldn’t know how.

I’m guessing, not to load other “dtbo” related to video/audio. That would mean,

###Disable auto loading of virtual capes (emmc/video/wireless/adc)
#disable_uboot_overlay_emmc=1
disable_uboot_overlay_video=1
disable_uboot_overlay_audio=1
#disable_uboot_overlay_wireless=1
#disable_uboot_overlay_adc=1

I tried both loaded and not loaded. PWM0 works both situations.

16

Can I see your full u-boot log

17

Yeah correct, by default HDMI video and audio is enabled, even without the HDMI plugged in

18 
=\~=\~=\~=\~=\~=\~=\~=\~=\~=\~=\~= PuTTY log 2025.12.08 09:36:35 =\~=\~=\~=\~=\~=\~=\~=\~=\~=\~=\~=

U-Boot SPL 2018.09-00002-g0b54a51eee (Sep 10 2018 - 19:41:39 -0500)
Trying to boot from MMC2
Loading Environment from EXT4…
\*\* Unable to use mmc 0:1 for loading the env \*\*

U-Boot 2018.09-00002-g0b54a51eee (Sep 10 2018 - 19:41:39 -0500), Build: jenkins-github_Bootloader-Builder-65

CPU  : AM335X-GP rev 2.1
I2C:   ready
DRAM:  512 MiB
No match for driver ‘omap_hsmmc’
No match for driver ‘omap_hsmmc’
Some drivers were not found
Reset Source: Power-on reset has occurred.
RTC 32KCLK Source: External.
MMC:   OMAP SD/MMC: 0, OMAP SD/MMC: 1
Loading Environment from EXT4…
\*\* Unable to use mmc 0:1 for loading the env \*\*
Board: BeagleBone Black
 not set. Validating first E-fuse MAC
BeagleBone Black:
BeagleBone: cape eeprom: i2c_probe: 0x54:
BeagleBone: cape eeprom: i2c_probe: 0x55:
BeagleBone: cape eeprom: i2c_probe: 0x56:
BeagleBone: cape eeprom: i2c_probe: 0x57:
Net:   eth0: MII MODE
cpsw, usb_ether
Press SPACE to abort autoboot in 2 seconds
board_name=\[A335BNLT\] …
board_rev=\[00C0\] …
switch to partitions #0, OK
mmc0 is current device
SD/MMC found on device 0
switch to partitions #0, OK
mmc0 is current device
Scanning mmc 0:1…
gpio: pin 56 (gpio 56) value is 0
gpio: pin 55 (gpio 55) value is 0
gpio: pin 54 (gpio 54) value is 0
gpio: pin 53 (gpio 53) value is 1
switch to partitions #0, OK
mmc0 is current device
gpio: pin 54 (gpio 54) value is 1
Checking for: /uEnv.txt …
Checking for: /boot.scr …
Checking for: /boot/boot.scr …
Checking for: /boot/uEnv.txt …
btrfs_read_superblock: invalid checksum at superblock mirror 0
btrfs_read_superblock: invalid checksum at superblock mirror 1
btrfs_read_superblock: No valid BTRFS superblock found!
\*\* Unrecognized filesystem type \*\*
gpio: pin 55 (gpio 55) value is 1
2259 bytes read in 9 ms (245.1 KiB/s)
Loaded environment from /boot/uEnv.txt
Checking if uname_r is set in /boot/uEnv.txt…
gpio: pin 56 (gpio 56) value is 1
Running uname_boot …
loading /boot/vmlinuz-6.12.49-bone36 …
8790528 bytes read in 564 ms (14.9 MiB/s)
debug: \[enable_uboot_overlays=1\] …
debug: \[enable_uboot_cape_universal=\] …
debug: \[uboot_base_dtb_univ=am335x-boneblack-uboot.dtb\] …
uboot_overlays: \[uboot_base_dtb=am335x-boneblack-uboot.dtb\] …
uboot_overlays: Switching too: dtb=am335x-boneblack-uboot.dtb …
loading /boot/dtbs/6.12.49-bone36/am335x-boneblack-uboot.dtb …
96616 bytes read in 40 ms (2.3 MiB/s)
uboot_overlays: \[fdt_buffer=0x60000\] …
uboot_overlays: unable to find \[mmc 0:3 BB-EHRPWM1-P9_14-P9_16.dtbo\]…
uboot_overlays: unable to find \[mmc 0:3 /lib/firmware/BB-BONE-eMMC1-01-00A0.dtbo\]…
uboot_overlays: unable to find \[mmc 0:3 /lib/firmware/BB-HDMI-TDA998x-00A0.dtbo\]…
uboot_overlays: unable to find \[mmc 0:3 /lib/firmware/BB-ADC-00A0.dtbo\]…
uboot_overlays: unable to find \[mmc 0:3 AM335X-PRU-UIO-00A0.dtbo\]…
uboot_overlays: add \[enable_uboot_cape_universal=1\] to /boot/uEnv.txt to enable…
loading /boot/initrd.img-6.12.49-bone36 …
12361257 bytes read in 790 ms (14.9 MiB/s)
debug: \[console=ttyS0,115200n8 root=/dev/mmcblk0p3 ro rootfstype=ext4 rootwait fsck.repair=yes earlycon coherent_pool=1M net.ifnames=0 lpj=1990656 rng_core.default_quality=100\] …
debug: \[bootz 0x82000000 0x88080000:bc9e29 0x88000000\] …

## Flattened Device Tree blob at 88000000

Booting using the fdt blob at 0x88000000
Loading Ramdisk to 8f436000, end 8ffffe29 … OK
Loading Device Tree to 8f41b000, end 8f435967 … OK

Starting kernel …
19

yeah… that’s very old…

sudo /opt/u-boot/bb-u-boot-am335x-evm/install.sh
20

The image was downloaded was BeagleBone Black Debian 13 2025-09-05 IoT (v6.12.x).