Page 1 of 1

pin mux setting (bcm2710-rpi-cm3, dt-blob config.txt)

Posted: Wed Sep 19, 2018 3:06 pm
by inac
Hello,

I’m trying to set the pin mux at the right values and I want to do that as early as possible.

What I see is that I can use the dt-blob.dts or the overlay method.

The preferred method is the dt-blob.dts way. But the firmware/kernel source doesn’t have the dt-blob.dts file anymore. So I have the following questions.

1) Is the dt-blob.dts replaced by bcm2710-rpi-cm3.dts or is the dt-blob.dts completely obsolete?
2) Wat is the purpose of the bcm2710-rpi-cm3.dts file?
3) Is there a big time gap between the default setting (bootloader) of the mux and the execution of the config.txt settings?
4) Will the dt-blob.dts still work?

Kind regards,

Re: pin mux setting (bcm2710-rpi-cm3, dt-blob config.txt)

Posted: Wed Sep 19, 2018 3:14 pm
by 6by9
inac wrote:
Wed Sep 19, 2018 3:06 pm
I’m trying to set the pin mux at the right values and I want to do that as early as possible.

What I see is that I can use the dt-blob.dts or the overlay method.

The preferred method is the dt-blob.dts way. But the firmware/kernel source doesn’t have the dt-blob.dts file anymore. So I have the following questions.
??? https://github.com/raspberrypi/firmware ... t-blob.dts
inac wrote:1) Is the dt-blob.dts replaced by bcm2710-rpi-cm3.dts or is the dt-blob.dts completely obsolete?
dt-blob.dts configures the firmware and sets the initial GPIO state. bcm27xx*.dts configure the Linux kernel.
inac wrote:2) Wat is the purpose of the bcm2710-rpi-cm3.dts file?
It configures the Linux kernel.
inac wrote:3) Is there a big time gap between the default setting (bootloader) of the mux and the execution of the config.txt settings?
A few hundred ms if booting from SD card. Longer if booting from USB or network.
It sounds like you're trying to do something wrong if you have any form of hard time contraints on GPIOs adopting particular values.
inac wrote:4) Will the dt-blob.dts still work?
Yes.

Why not use the gpio command in config.txt - https://www.raspberrypi.org/forums/view ... 7&t=208748
That gets around the fact that dt-blob.dts can't act as an overlay and so is a pain from a maintenance perspective.

Re: pin mux setting (bcm2710-rpi-cm3, dt-blob config.txt)

Posted: Thu Sep 20, 2018 2:18 pm
by inac
Thank you, that clears a lot!

I was probably searching in the Linux directory. If there is a few hundred ms it doesn't make much difference. In case of many second I would not prefer overlays.

It's that I used a pin with a default pull-up but need a pull-down and on my board there is a strong pull-down. So it works but not is not optimal. Until I can fix the HW I want to set the right values as quick as possible.

Kind regards