Beaglebone AI Device Tree Overlay syntax

General Discussion
1

I’m looking for help understanding the device tree overlay syntax. As an example, let’s say I’m trying to configure P8.12 to be a PRU input with a pull up.

This overlay configures P8.12 as a PRU input, but doesn’t have the pull up:

I see the definition for P8_12_pruin_pin

PIN_INPUT could easily be changed to PIN_INPUT_PULLUP in the P8_12_pruin_pin definition, but I’d like to only make changes my own overlay. I can’t figure out how to do that, though. What change to BBAI-PRUIN_PRU1_0.dts would configure P8_12 to be a PRU input pull up?

2

Hi @pocketnc_john as long as you are running the v4.19.x-ti kernel, just clone that repo, make the change and run:

make
sudo make install
sudo reboot

and on boot-up, your pin would have the change…

Regards,

3

Right, and I have that going, but I’d prefer not to change the global am5729-beagleboneai.dtb. Instead, I’d like to only change my individual overlay. Is there a way to achieve that? I’m not familiar enough with the device tree syntax to know.

I would guess something like this in the overlay, but I can’t figure out the right syntax:

@ocp {

    P8_12_pinmux { pinctrl-0 = pinmux_P8_12_pruin_pin { pinctrl-single,pins = <
		P8_12( PIN_INPUT_PULLUP | MUX_MODE12) >; };
}
4

Ah sorry, so to configure it only for you, you need to play this game:

Disable it:

Define it:

and then, use it

Regards,

5

Thanks Robert,

Turns out I had a couple things wrong. First, I wasn’t including the proper headers to get the P8_12, PIN_INPUT_PULLUP, and MUX_MODE12 macros. dtc was helpful enough to report something was wrong exactly at those macros, but it took me a while to make the connection that it was because they weren’t defined.

Next, defining a new P8_12_pruin_pu_pin entry under &dra7_pmx_core worked from my overlay (rather than trying to stick the definition into the ocp pinctrl-0 entry some how.

So, the particular modifications for the initial example would result in:

/dts-v1/;
/plugin/;

// Add this to get PIN_INPUT_PULLUP and MUX_MODE12 macros
#include <dt-bindings/pinctrl/dra.h>

// Add this to get P8_12 macro
#include <dt-bindings/board/am572x-bone-pins.h>

&{/chosen} {
    overlays {
        BBAI-PRUIN_PRU1_0 = __TIMESTAMP__;
    };
};

// Add a new pin mode for PRU input pullup
&dra7_pmx_core {
  P8_12_pruin_pu_pin: pinmux_P8_12_pruin_pu_pin { pinctrl-single,pins = <
    P8_12( PIN_INPUT_PULLUP | MUX_MODE12) >; };
}

&ocp {
    P8_11_pinmux { pinctrl-0 = <&P8_11_pruin_pin>; }; /* pr1_pru0_gpi4 */

// Use the new 8.12 PRU input pullup definition from above
    P8_12_pinmux { pinctrl-0 = <&P8_12_pruin_pu_pin>; }; /* pr1_pru0_gpi3 */

    P9_15_pinmux { pinctrl-0 = <&P9_15_pruin_pin>; }; /* pr1_pru0_gpi5 */
    P9_26_pinmux { pinctrl-0 = <&P9_26_pruin_pin>; }; /* pr1_pru0_gpi17 */
};
1 Like