Problems with PWM Sound output on RPi Zero W

THaase · April 7, 2017 at 9:07 AM

Hi to all of you!

I'm just new to LibreELEC 8.0.1 official build (used OpenELEC before on a ITX PC Board) and wanted to set up a second system on an RPi Zero W.

Everything is fine so far, but I'm having problems getting PWM Output working on the Zero.

What I've done so far:

Altered the config.txt with the following lines:

Code

# Remap PWM Out Pins for Audio
dtparam=audio=on
dtoverlay=pwm-2chan,pin=18,func=2,pin2=13,func2=4
audio_pwm_mode=2


# Set up LIRC
dtoverlay=lirc-rpi,gpio_out_pin=15,gpio_in_pin=17


# CVBS PAL
sdtv_mode=2    # Normal PAL

Display More

Most likely the 'dtparam=audio=on' isn't needed at all, nevertheless I've tested a lot of stuff in the meanwhile.
(Lirc is working as expected - Picture is fine on PAL TV)
I've soldered my band-pass to the according pins.

As I don't hear anything I've started to try to debug the system.

Code

LibreELEC:~ # lsmod
Module                  Size  Used by
hci_uart               17434  1
btbcm                   5989  1 hci_uart
bluetooth             311780  23 hci_uart,btbcm
bridge                 93509  0
stp                     1323  1 bridge
llc                     3224  2 bridge,stp
snd_bcm2835            18434  0
brcmfmac              186291  0
snd_pcm                69875  1 snd_bcm2835
brcmutil                5069  1 brcmfmac
snd_timer              17204  1 snd_pcm
snd                    43049  3 snd_timer,snd_bcm2835,snd_pcm
cfg80211              256604  1 brcmfmac
rfkill                 14411  5 bluetooth,cfg80211
bcm2835_gpiomem         2759  0
lirc_rpi                6120  3
lirc_dev                7253  1 lirc_rpi
rc_core                17302  1 lirc_dev
fixed                   2381  0

Display More

So basically the drivers seems to be loaded.

Therefor I've additionally checkedthe gpio assignment:

Code

LibreELEC:~ # cat /sys/kernel/debug/gpio
gpiochip0: GPIOs 0-53, parent: platform/20200000.gpio, pinctrl-bcm2835:
 gpio-47  (                    |?                   ) out lo

Mhh - wondering a little bit ..... the lirc is working ... but also not there .....

Check available devices with aplay:

Code

LibreELEC:~ # aplay -l
**** List of PLAYBACK Hardware Devices ****
card 0: ALSA [bcm2835 ALSA], device 0: bcm2835 ALSA [bcm2835 ALSA]
  Subdevices: 8/8
  Subdevice #0: subdevice #0
  Subdevice #1: subdevice #1
  Subdevice #2: subdevice #2
  Subdevice #3: subdevice #3
  Subdevice #4: subdevice #4
  Subdevice #5: subdevice #5
  Subdevice #6: subdevice #6
  Subdevice #7: subdevice #7
card 0: ALSA [bcm2835 ALSA], device 1: bcm2835 ALSA [bcm2835 IEC958/HDMI]
  Subdevices: 1/1
  Subdevice #0: subdevice #0
LibreELEC:~ #

Display More

Basically looks good .....

Now I've tried to playback some sounds with aplay.

Code

LibreELEC:~ # aplay -Dhw:0,0 /usr/share/kodi/addons/resource.uisounds.kodi/resources/notify.wav
Playing WAVE '/usr/share/kodi/addons/resource.uisounds.kodi/resources/notify.wav' : Signed 16 bit Little Endian, Rate 32000 Hz, Mono
LibreELEC:~ #

NOTHING TO HEAR - this thing is driving me crazy

Maybe a bug / short in my filters?
Written some small bash script ....

Bash

#!/bin/bash
#   Exports pin to userspace
echo "18" > /sys/class/gpio/export
echo "13" > /sys/class/gpio/export


# Sets pin 18 as an output
echo "out" > /sys/class/gpio/gpio18/direction
echo "out" > /sys/class/gpio/gpio13/direction


COUNTER=0
while [  $COUNTER -lt 10000 ]; do
  echo The counter is $COUNTER
  let COUNTER=COUNTER+1
  echo "1" > /sys/class/gpio/gpio18/value
  echo "0" > /sys/class/gpio/gpio18/value
  echo "1" > /sys/class/gpio/gpio13/value
  echo "0" > /sys/class/gpio/gpio13/value
done

Display More

Testing - I HEAR SOME NOISE .... so the HW seems to be fine.

So I've NO idea how to ge further .....
(For sake of completeness I've attached the dmesg)

Basically I can set up a full distro and try some tests with that .....
But this could easily cost me hours more ....

So - does anybody has working PWM Sound with LibeELEC 8.0.1 on a Pi Zero?

Thanks in advance for your help!!

cu
Thomas

**popcornmix** · April 7, 2017 at 1:55 PM

Can you just confirm that you have selected analogue audio output (rather than hdmi) in system/audio settings?

THaase · April 7, 2017 at 2:19 PM

Quote from popcornmix

Can you just confirm that you have selected analogue audio output (rather than hdmi) in system/audio settings?

Yes - or most likely I'm pretty sure. I can test again.
At the moment the selection is on HDMI & Analog.
This definitely don't work.
Nevertheless: Should I not be able to playback with aplay?
At least the device is not blocked

Cu
Thomas

**popcornmix** · April 7, 2017 at 2:50 PM

aplay will output to the default device, which will be hdmi if a hdmi display supporting audio is attached (is it?)
You can force pwm output with:

Code

amixer cset numid=3 1

THaase · April 7, 2017 at 5:20 PM

Sorry forgot to mention:
I've used the amixer command before using aplay.

Das_OSi · April 8, 2017 at 10:49 AM

Quote from THaase

So - does anybody has working PWM Sound with LibeELEC 8.0.1 on a Pi Zero?

Same problem here =(

Tried to add

"hdmi_ignore_edid_audio=1
hdmi_force_edid_audio=0
dtoverlay=pwm-2chan,pin=18,func=2,pin2=13,func2=4"

to my config.txt - no sound at all.

THaase · April 8, 2017 at 11:05 AM

Quote from Das_OSi

Same problem here =(

Tried to add

"hdmi_ignore_edid_audio=1
hdmi_force_edid_audio=0
dtoverlay=pwm-2chan,pin=18,func=2,pin2=13,func2=4"

to my config.txt - no sound at all.

Good to hear that I'm not alone ....
Bad to hear that it doesn't seems to be my fault.

I've tried the different sound settings in Kodi in the meanwhile :

Analog -> no sound
HDMI & Analog -> no sound

If any more logs are required I can provide.

HDMI I've not tested till now (will not be able to do this before tomorrow (have 3.5 year old twins that are awake in the meanwhile) - hopefully tomorrow morning.

Everything else woks fine in the meanwhile - except for sound (via PWM).

THaase · April 9, 2017 at 8:20 AM

I've done some more tests in the meanwhile:

1.) Sound via HDMI is working as expected.
2.) Using 'dtoverlay=pwm,pin=13,func=4' (for mono output instead stereo) -> ALSO NO SOUND

So it seems to be more a general pwm problem instead of something related to the stereo one.

**popcornmix** · April 10, 2017 at 11:20 AM

My colleague Phil has testes the pwm-2chan overlay on a Pi0W and it is working.

Can you try removing "audio_pwm_mode=2"?
I don't think that is the problem, but it is a non-standard option that should be ruled out.

Can you try running raspi-gpio. Here is version from raspbian that should work on LE
uc?id=0B-6zmEDJwxZEY1RXb0ZpNi04VEU&export=download

Report output of "./raspi-gpio get" with the pwm-2chan overlay present.

THaase · April 10, 2017 at 11:46 AM

Quote from popcornmix

My colleague Phil has testes the pwm-2chan overlay on a Pi0W and it is working.

Can you try removing "audio_pwm_mode=2"?
I don't think that is the problem, but it is a non-standard option that should be ruled out.

Can you try running raspi-gpio. Here is version from raspbian that should work on LE
uc?id=0B-6zmEDJwxZEY1RXb0ZpNi04VEU&export=download

Report output of "./raspi-gpio get" with the pwm-2chan overlay present.

Hi popcornmix,

thanks for reporting!
Good to know that the problem is on my side

I'm pretty sure that I've also tested without having the "audio_pwm_mode=2" in config.txt (put this in during my tests to solve the problem) ... but I'll test again.

It might took till tomorrow morning (also the gpio test) .... (Pi is at home, I'm at work)

Thanks a lot!

THaase · April 11, 2017 at 4:52 PM

So I've done some more ...

I've used raspi-gpio to get the status of the different gpios:

Code

LibreELEC:~ # /flash/raspi-gpio get
BANK0 (GPIO 0 to 27):
  GPIO 00: level=1 fsel=0 alt=  func=INPUT
  GPIO 01: level=1 fsel=0 alt=  func=INPUT
  GPIO 02: level=1 fsel=0 alt=  func=INPUT
  GPIO 03: level=1 fsel=0 alt=  func=INPUT
  GPIO 04: level=1 fsel=0 alt=  func=INPUT
  GPIO 05: level=1 fsel=0 alt=  func=INPUT
  GPIO 06: level=1 fsel=0 alt=  func=INPUT
  GPIO 07: level=1 fsel=0 alt=  func=INPUT
  GPIO 08: level=1 fsel=0 alt=  func=INPUT
  GPIO 09: level=0 fsel=0 alt=  func=INPUT
  GPIO 10: level=0 fsel=0 alt=  func=INPUT
  GPIO 11: level=0 fsel=0 alt=  func=INPUT
  GPIO 12: level=0 fsel=0 alt=  func=INPUT
  GPIO 13: level=0 fsel=0 alt=  func=INPUT
  GPIO 14: level=0 fsel=0 alt=  func=INPUT
  GPIO 15: level=0 fsel=1 alt=  func=OUTPUT
  GPIO 16: level=0 fsel=0 alt=  func=INPUT
  GPIO 17: level=1 fsel=0 alt=  func=INPUT
  GPIO 18: level=0 fsel=0 alt=  func=INPUT
  GPIO 19: level=0 fsel=0 alt=  func=INPUT
  GPIO 20: level=0 fsel=0 alt=  func=INPUT
  GPIO 21: level=0 fsel=0 alt=  func=INPUT
  GPIO 22: level=0 fsel=0 alt=  func=INPUT
  GPIO 23: level=0 fsel=0 alt=  func=INPUT
  GPIO 24: level=0 fsel=0 alt=  func=INPUT
  GPIO 25: level=0 fsel=0 alt=  func=INPUT
  GPIO 26: level=0 fsel=0 alt=  func=INPUT
  GPIO 27: level=0 fsel=0 alt=  func=INPUT
BANK1 (GPIO 28 to 45):
  GPIO 28: level=1 fsel=4 alt=0 func=SDA0
  GPIO 29: level=1 fsel=4 alt=0 func=SCL0
  GPIO 30: level=0 fsel=7 alt=3 func=CTS0
  GPIO 31: level=0 fsel=7 alt=3 func=RTS0
  GPIO 32: level=1 fsel=7 alt=3 func=TXD0
  GPIO 33: level=1 fsel=7 alt=3 func=RXD0
  GPIO 34: level=1 fsel=7 alt=3 func=SD1_CLK
  GPIO 35: level=1 fsel=7 alt=3 func=SD1_CMD
  GPIO 36: level=1 fsel=7 alt=3 func=SD1_DAT0
  GPIO 37: level=1 fsel=7 alt=3 func=SD1_DAT1
  GPIO 38: level=1 fsel=7 alt=3 func=SD1_DAT2
  GPIO 39: level=1 fsel=7 alt=3 func=SD1_DAT3
  GPIO 40: level=0 fsel=1 alt=  func=OUTPUT
  GPIO 41: level=1 fsel=1 alt=  func=OUTPUT
  GPIO 42: level=0 fsel=0 alt=  func=INPUT
  GPIO 43: level=0 fsel=4 alt=0 func=GPCLK2
  GPIO 44: level=0 fsel=1 alt=  func=OUTPUT
  GPIO 45: level=1 fsel=1 alt=  func=OUTPUT
BANK2 (GPIO 46 to 53):
  GPIO 46: level=1 fsel=0 alt=  func=INPUT
  GPIO 47: level=0 fsel=1 alt=  func=OUTPUT
  GPIO 48: level=0 fsel=4 alt=0 func=SD0_CLK
  GPIO 49: level=1 fsel=4 alt=0 func=SD0_CMD
  GPIO 50: level=1 fsel=4 alt=0 func=SD0_DAT0
  GPIO 51: level=1 fsel=4 alt=0 func=SD0_DAT1
  GPIO 52: level=1 fsel=4 alt=0 func=SD0_DAT2
  GPIO 53: level=1 fsel=4 alt=0 func=SD0_DAT3
LibreELEC:~ #

Display More

Mhhh ---- the GPIO18 and 13 are not configured for PWM ....

So I've give it a try:

Code

LibreELEC:~ # /flash/raspi-gpio set 18 a5
LibreELEC:~ # /flash/raspi-gpio set 13 a0

And ... I've been able to play sound with aplay (after amixer).....

But it's not a real solution ... as the root is squashfs and ro I can not alter the filesystem .....
I would have to do it by my own ....
Will be overwritten by the next update .....

Not a solution

So I've looked for something different .... and found it:

pwm-audio-pizero/pwm-audio-pi-zero-overlay.dtbo at master · ian57/pwm-audio-pizero · GitHub

I've added the file to the overlay directory and used it by adding:

Code

dtoverlay=pwm-audio-pi-zero-overlay

And now it works

I've no real idea why the pwm-2chan.dtbo doesn't work, but this solution works and is update resistant.

Thanks a lot for your help!