PPS overlay for a Beaglebone Black with a 6.15 kernel on debian trixie

README.md

Notes

This took much longer to do than I expected. There seems to be a LOT of old information (hey, the BBB came out in April 2013), and examples seemed to include lots of 'fragment' sections that weren't in newer overlays. I was originally going to do a single overlay that monitored some other GPIOs raised by my RFZERO board, however for now I just include uart1 (to pick up the serial from GPS) and this overlay to configure the BBB as an NTP server.

I'll put a few more words on my blog once I've finished tweaking chrony / gpsd configs

Compiling

Because of the #include formatted lines, you'll need to pre-process this with cpp. I was unaware that the sources are already in /opt/source so I downloaded the overlays from GitHub and added mine.

cd BeagleBoard-DeviceTrees/
cpp -nostdinc -I include -I arch  -undef -x assembler-with-cpp ../PPS-00A0.dts > PPS-00A0.dtso
dtc -@ -O dtb -o PPS-00A0.dtbo PPS-00A0.dtso
cp PPS-00A0.dtbo /boot/dtbs/$(uname -r)/overlays/

And then add the overlay to your uEnv.txt

uname_r=6.15.10-bone26
enable_uboot_overlays=1
uboot_overlay_addr0=BB-UART1-00A0.dtbo
uboot_overlay_addr1=PPS-00A0.dtbo
disable_uboot_overlay_video=1
disable_uboot_overlay_audio=1
disable_uboot_overlay_wireless=1
uboot_overlay_pru=AM335X-PRU-UIO-00A0.dtbo
console=ttyS0,115200n8
cmdline=fsck.repair=yes earlycon coherent_pool=1M net.ifnames=0 lpj=1990656 rng_core.default_quality=100

PPS-00A0.dts

// SPDX-License-Identifier: GPL-2.0-only
/* 
 * Overlay to accept a PPS input from GPS device on P9_12.
 * Andrew Elwell <[email protected]>, Aug 2025
 * Thanks to pointers on Discord and BB Forums
 */

/dts-v1/;
/plugin/;

#include <dt-bindings/gpio/gpio.h>
#include <dt-bindings/pinctrl/am33xx.h>
#include <dt-bindings/interrupt-controller/irq.h>

/*
 * Helper to show loaded overlays under: /proc/device-tree/chosen/overlays/
 */
&{/chosen} {
	overlays {
		PPS-00A0.bb.org-overlays = __TIMESTAMP__;
	};
};

&ocp {
	P9_12_pinmux { status = "disabled"; };	/* pps */
};

&am33xx_pinmux {
	bb_pps_gpio_pins: pinmux_pps_gpio_pins {
		pinctrl-single,pins = <
			AM33XX_PADCONF(AM335X_PIN_GPMC_BEN1, PIN_INPUT_PULLDOWN, MUX_MODE7)	/* P9_12 pps_gpio */
		>;
	};
};

&{/} {
	pps {
		status = "okay";
		compatible = "pps-gpio";
		pinctrl-names = "default";
		pinctrl-0 = <&bb_pps_gpio_pins>;
		gpios = <&gpio1 28 GPIO_ACTIVE_HIGH>;
	};
};

Hey, you have no idea how awesome the timing on this was for me. I started researching using my BBB as a stratum 1 time server and gpsd server like a week ago. JUST got my gps module with PPS output in today and stumbled on this that you posted only a couple days ago. Thrilled to let you know that it worked perfectly for me, even on Bookworm and already got it up and running.

Thanks!