PWM audio driver source code for Raspberry Pi

shabaz over 12 years ago

(Still getting to grips with this site, created a blog entry by mistake!)

Apologies if this is the wrong location on the forum.

I'm new to Linux driver coding (but very experienced in application coding in C and C++).

I've spent some time searching for source code for the rasp-pi.

I was wondering, where can I find the source code for the PWM audio driver?

(that is used for the on-board audio, not via HDMI).

I've found this location:

https://github.com/raspberrypi/linux/blob/rpi-patches/sound/arm and I think the function

I'm looking for is called bcm2835_audio_write but I don't know where that function source code

resides.

Any quick pointers to direct me to the particular file I should be looking at would be much appreciated.

Thanks!

fustini over 12 years ago
Hi, not sure if this is what you need, but I happened to be reading this post by Adafruit just before seeing your post:

New! Adafruit’s PWM/Servo kernel module for easy PWM/Servo control on GPIO#18
http://www.adafruit.com/blog/2012/08/31/update-occidentalis-v0-2-adafruits-raspberry-pi-educational-linux-distro/

Looking at their github repo, there are several recent commits for pwm:

https://github.com/adafruit/adafruit-raspberrypi-linux/commits/rpi-patches/

The last commit was to:

drivers/misc/rpi-pwm.c
https://github.com/adafruit/adafruit-raspberrypi-linux/commit/4a41db242545d5f86f8a759d81f4ee1b915bd461

cheers,
drew
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Former Member over 10 years ago

Hi shabaz!

Have you solved this problem?
I have the same problem, I need a PWM signal to 200 KHz for libraries but I use can only generate a PWM signal from 5 KHz (according to my oscioscopio).

Will you kindly give me guidance.

Thank you
toto
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shabaz over 10 years ago in reply to Former Member

Hi toto,

Unfortunately I abandoned efforts to use the audio when the BeagleBone Black came along (it has hardware capabilities useful for PWM and separate processors for high-speed I/O).
However on the RPI, I notice there is some code here which states it uses some "semi-hardware pulse width modulation"? This might be a better approach than using audio.

"RPIO.PWM provides PWM via DMA for the Raspberry Pi, using the onboard PWM module for semi-hardware pulse width modulation with a precision of up to 1µs."
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