Re: RPI4 Hardware PWM

From: Matthew Grooms <mgrooms_at_shrew.net>
Date: Wed, 9 Jun 2021 16:16:49 -0500
On 6/8/2021 4:06 PM, Matthew Grooms wrote:
> Hey All,
>
> I have a project I'm working on that depends on interfacing with a few 
> sensor modules using both i2c and PWM. I've got the i2c devices to 
> work correctly, but I'm not sure how to interface with the HW PWM 
> support of the RPI4. I can see there are settings exposed via sysctl 
> for Beaglebone systems ...
>
> https://zewaren.net/bbb-pwm.html
>
> I was hoping I'd be able to force GPIO 12 or 13 into ALT0  and set the 
> duty values via sysctl, but that doesn't seem to be an option. Any 
> help would be greatly appreciated.

Replying to myself with a bit more info. I see that there is a driver 
available for rpi boards authored by PHK ...

https://cgit.freebsd.org/src/tree/sys/arm/broadcom/bcm2835/bcm2835_pwm.c

That has notes on RPi2/3 boards, but not mention of RPi4. When I load 
that, I see the following output ...

Jun  9 18:29:50 generic kernel: pwm0: <BCM2708/2835 PWM controller> mem 
0x7e20c000-0x7e20c027 on simplebus0
Jun  9 18:29:50 generic kernel: pwm0: cannot find Clock Manager

I assume I'm doing something wrong. Any feedback would be greatly 
appreciated.

Thanks,

-Matthew
Received on Wed Jun 09 2021 - 21:16:49 UTC

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