PPS in GPIO pin, device tree configuration

Software SW help
,
#1

Hello, I am currently trying to use a GPS for an accurate Network Time Protocol.

The router I am using is a Turris Omnia 2020(https://www.turris.com/en/omnia/overview/) and the gps is a sintrones VDB-810DR(https://www.sintrones.com/VDB-810DR.html).

I managed to conect the gps through usb and got it working. I also connected the PPS from the GPS to the GPIO44(MPP44) pin on the board, but I don’t know how I should configure the GPIO pin in the device tree(.dts file). The goal is to get the kmod-pps-gpio driver working.

I am building onto the openwrt open-source code.

#2

All you need is the “dtc” package to de/-compile the existing dtb on the /boot partition.
I modified it (Release 5.x.x) this way:

--- armada-385-turris-omnia-phy.dts	2020-06-08 13:39:12.603583058 +0200
+++ armada-385-turris-omnia-phy-pps.dts	2020-06-08 13:44:53.589760925 +0200
@@ -466,6 +466,8 @@
 				#interrupt-cells = <0x02>;
 				interrupts = <0x00 0x35 0x04 0x00 0x36 0x04 0x00 0x37 0x04 0x00 0x38 0x04>;
 				clocks = <0x04 0x00>;
+				linux,phandle = <0x1e>;
+				phandle = <0x1e>;
 			};
 
 			gpio@18140 {
@@ -1055,4 +1057,11 @@
 		los-gpios = <0x1d 0x03 0x00>;
 		mod-def0-gpios = <0x1d 0x04 0x01>;
 	};
+
+	pps@18 {
+		gpios = <0x1e 0x12 0x0>;
+		compatible = "pps-gpio";
+		status = "okay";
+	};
+
 };

As you can see I’m using GPIO18 (Pin1: https://wiki.turris.cz/doc/_media/omnia-pinout.png)
Works great with my uputronics uBLOX MAX-M8Q.

I use gpsd+chrony to discipline the clock. Keep an eye on the default busybox/sysntpd which gets reactivated with every update and conflicts with chronyd.

For chronyd I use

refclock SHM 0 poll 3 refid UBLX offset 0.2 noselect
refclock PPS /dev/pps0 lock UBLX refid GPS

in chrony.conf.

gspd is running with

/usr/sbin/gpsd -N -n -S 2947 /dev/ttyS1 /dev/pps0

Since I use this since Turris OS 3.x I’m currently not sure if I modified the init script or if it’s the default from OS 5 to handle /etc/config/gpsd with

config gpsd 'core'
        option enabled '1'
        option device '/dev/ttyS1'
        option ppsdev '/dev/pps0'
        option port '2947'
        option listen_globally '0'

accordingly.

1 Like
#3

Thank you very much for the quick response!
We are working on this device tree: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/tree/arch/arm/boot/dts/armada-385-turris-omnia.dts?h=v5.4.80
Could you show me how the changes you included in you answer would apply to this code and on the gpio pin 44?

Thank you for the help,
Razvan

#4

Sorry. I’m far from being an device-tree expert. I managed to decompile the existing binary tree, modify it based on RaspberryPi dtoverlay pps-gpio and recompile it. I’ve no idea were all the missing information from your kernel tree is added to build what I see on my omnia. Especially the sections gpio@18100 and gpio@18140.

Basically I added the next free phandle to gpio@18100 IIRC and used it in the pps@ section. It should work if you change pps@18 to pps@44 to use that pin.

But as I said. I’m far from expert on this topic. Maybe someone from Turris can help?

#5

Ok, thanks!

I managed to get it working in the end. This is how my .dts patch looks like:

--- a/arch/arm/boot/dts/armada-385-turris-omnia.dts_orig	2020-12-02 15:10:37.810000000 +0100
+++ b/arch/arm/boot/dts/armada-385-turris-omnia.dts	2020-12-02 15:10:52.780000000 +0100
@@ -34,6 +34,14 @@
 		reg = <0x00000000 0x40000000>; /* 1024 MB */
 	};
 
+	pps {
+		compatible = "pps-gpio";
+		pinctrl-names = "default";
+		pinctrl-0 = <&pps_pins>;
+		gpios = <&gpio1 26 GPIO_ACTIVE_HIGH>;
+		status = "okay";
+	};
+
 	soc {
 		ranges = <MBUS_ID(0xf0, 0x01) 0 0xf1000000 0x100000
 			  MBUS_ID(0x01, 0x1d) 0 0xfff00000 0x100000
@@ -379,6 +387,11 @@
 		marvell,function = "gpio";
 	};
 
+	pps_pins: pps-pins {
+		marvell,pins = "mpp44";
+		marvell,function = "gpio";
+	};
+
 	spi0cs0_pins: spi0cs0-pins {
 		marvell,pins = "mpp25";
 		marvell,function = "spi0";
#6

In case somebody needs a modified device-tree for TOS 6.0.x… basically the same as above, except the new (higher) phandle…

--- armada-385-turris601-omnia-phy.dts	2022-10-22 14:48:32.338737610 +0200
+++ armada-385-turris601-omnia-phy-pps.dts	2022-10-22 15:02:20.638737610 +0200
@@ -475,6 +475,7 @@
 				#interrupt-cells = <0x02>;
 				interrupts = <0x00 0x35 0x04 0x00 0x36 0x04 0x00 0x37 0x04 0x00 0x38 0x04>;
 				clocks = <0x04 0x00>;
+				phandle = <0x25>;
 			};
 
 			gpio@18140 {
@@ -1150,4 +1151,11 @@
 		status = "disabled";
 		phandle = <0x10>;
 	};
+
+        pps@18 {
+                gpios = <0x25 0x12 0x0>;
+                compatible = "pps-gpio";
+                status = "okay";
+        };
+
 };
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