Pps-gpio for s905x

Software
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1

I am running Le Potato on Libre computer’s raspbian release. I am trying to use GPIOAO_6 for pps from a GPS module. This is the dts I have written:

/*
 * Overlay to enable PPS on GPIOAO_6
 */

/dts-v1/;
/plugin/;

#include <dt-bindings/gpio/gpio.h>
#include <dt-bindings/gpio/meson-gxl-gpio.h>

/ {
	compatible = "libretech,cc", "amlogic,s905x", "amlogic,meson-gxl";

	fragment@0 {
		target-path = "/";
		__overlay__ {
			pps {
				compatible = "pps-gpio";
				gpios = <&gpio GPIOAO_6 GPIO_ACTIVE_HIGH>;
			};
		};
	};
};

I compile, enable and merge this and get the following error in dmesg

[    8.309319] pps-gpio pps: failed to map GPIO to IRQ: -6
[    8.309343] pps-gpio: probe of pps failed with error -22

What should my .dts look like to use GPIOAO_6 for gpio-pps? Thanks.

2

I’m having the same issue - I tried on a different pin (gpios = <&gpio GPIOCLK_0 GPIO_ACTIVE_HIGH>;) and I got the same dmesg error.

3

I tried several different pins too. I can confirm that GPAIOAO_9 and GPIOAO_6 give the same error. I think the problem has something to do with how this Amlogic chip handles mapping interrupts to GPIO. I tried several different approaches with interrupts in the .dts too, but no success. Hopefully someone from libre will chime in with an example that works.

1 Like
4

Same problem for me too.

5

The overlay is incorrect. You cannot just create a root pps node. Take a look at other overlays.

6

@librecomputer Thank you for the reply. This is how Armbian handles a rockchip board and is what I used as my model.

/dts-v1/;
/plugin/;

/ {
  compatible = "pine64,rock64", "rockchip,rk3328";

  fragment@0 {
    target-path = "/";
    __overlay__ {
      pps: pps@0 {
        compatible = "pps-gpio";
        gpios = <&gpio GPIOAO_6 GPIO_ACTIVE_HIGH>;
      };
    };
  };
};

And this is how Armbian handles a H5 board.

/dts-v1/;
/plugin/;

/ {
	compatible = "allwinner,sun50i-h5";

	fragment@0 {
		target = <&pio>;
		__overlay__ {
			pps_pins: pps_pins {
				pins = "PD14";
				function = "gpio_in";
			};
		};
	};

	fragment@1 {
		target-path = "/";
		__overlay__ {
			pps@0 {
				compatible = "pps-gpio";
				pinctrl-names = "default";
				pinctrl-0 = <&pps_pins>;
				gpios = <&pio 3 14 0>; /* PD14 */
				status = "okay";
			};
		};
	};
};

Which .dts examples should I be looking at for pps-gpio on s905x? I have looked at the overlays here:

But there aren’t any pps examples. I realize now my pps { line should probably be pps@0 { but that didn’t work either. Any suggestion of an example would be appreciated.

7

GPIO_AO is part of the gpio_ao and not part of the gpio handle.

8

Has there been any progress made here? One of the best use cases for these ARM single board computers is to deploy them with a GNSS receiver to create a small and cost effective network time server - but PPS is absolutely required.

Does Libre Computer offer any sort of bug bounty program? I know that I would gladly contribute to having this issue be resolved…

1 Like
9

@librecomputer Thank you for the suggestion. This version:

/*
 * Overlay to enable PPS on GPIOAO_6
 */

/dts-v1/;
/plugin/;

#include <dt-bindings/gpio/gpio.h>
#include <dt-bindings/gpio/meson-gxl-gpio.h>
#include <dt-bindings/interrupt-controller/irq.h>
#include <dt-bindings/interrupt-controller/meson-gic.h>

/ {
        compatible = "libretech,cc", "amlogic,s905x", "amlogic,meson-gxl";

        fragment@0 {
                target-path = "/";
                __overlay__ {
                        pps@0 {
                                compatible = "pps-gpio";
                                gpios = <&gpio_ao GPIOAO_6 GPIO_ACTIVE_HIGH>;
                        };
                };
        };
};

After make && sudo make install && ldto merge pps-new and reboot I get this in my dmesg:

jeff@potato:~/git/libretech-wiring-tool/libre-computer/aml-s905x-cc/dt$ dmesg |grep pps
[    0.664522] pps_core: LinuxPPS API ver. 1 registered
[    0.664536] pps_core: Software ver. 5.3.6 - Copyright 2005-2007 Rodolfo Giometti <giometti@linux.it>
[    8.085724] pps-gpio pps@0: failed to map GPIO to IRQ: -6
[    8.085744] pps-gpio: probe of pps@0 failed with error -22
jeff@potato:~/git/libretech-wiring-tool/libre-computer/aml-s905x-cc/dt$

What is the proper way to assign an IRQ to a GPIO pin on this board?

10

An NTP server with PPS discipline is something I’m very interested in as well. Per some of the other posts and suggestions I’ve run the command dtc -I dtb -O dts pps-gpio.dtbo -o pps-gpio.dts on the raspberry pi device tree overlay located in /boot/overlays on the le potatoe current raspbian I’ve got on my board. This is the output, I’m not sure how to translate this -

/dts-v1/;
/plugin/;

/ {
	compatible = "brcm,bcm2708";
	fragment@0 {
		target-path = "/";
		__overlay__ {
			pps: pps@12 {
				compatible = "pps-gpio";
				pinctrl-names = "default";
				pinctrl-0 = <&pps_pins>;
				gpios = <&gpio 18 0>;
				status = "okay";
			};
		};
	};

	fragment@1 {
		target = <&gpio>;
		__overlay__ {
			pps_pins: pps_pins@12 {
				brcm,pins =     <18>;
				brcm,function = <0>;    // in
				brcm,pull =     <0>;    // off
			};
		};
	};

	__overrides__ {
		gpiopin = <&pps>,"gpios:4",
			  <&pps>,"reg:0",
			  <&pps_pins>,"brcm,pins:0",
			  <&pps_pins>,"reg:0";
		assert_falling_edge = <&pps>,"assert-falling-edge?";
		capture_clear = <&pps>,"capture-clear?";
	};
};
11

Do you guys have a device for us to purchase, test, and integrate into the wiring tool?

1 Like
12

This is the module I’m looking at, but any similiar device should do. It has a UBLOX neo 6 module I believe.

GT-U7 GPS module
UBLOX Datasheet

One thing I’m considering at this point is applying the dt overlay that makes uarta include RTS and CTS. Then feeding the pps into CTS. The old school way of making an NTP server applied the PPS to the DCD of the UART. This would require using gpsd to interface between the gps and ntp/chrony. The ppscheck utility included with gpsd indicates will sense pps applied to a UART CTS, so hopefully gpsd would as well. It really all boils down to getting the pps pulse to generate an interrupt somehow.

13

No sucess yet. I’ve added the uarta cts-rts dt overlay (sudo ldto merge uart-a-rts-cts). The GT-U7 listed above is connected -

Potatoe ----- GPS
pin 4 5v — gps v in
pin 6 gnd — gps gnd
pin 8 uarta tx — gps rx
pin10 uarta rx — gps tx
pin12 uarta cts — gps pps (100 ms pulse at start of each second)

The gpsd daemon is started (sudo gpsd -D 5 -N -n /dev/ttyAML6). gpsd connects via uarta and controls and configures the gps device. However the pps is not received via uarta cts.
gpsd messages --------
gpsd:INFO: gpsd_activate(2): activated GPS (fd 5)
gpsd:PROG: NTP:PPS: using SHM(0)
gpsd:PROG: NTP:PPS: using SHM(1)
gpsd:PROG: PPS:/dev/ttyAML6 chrony socket /run/chrony.ttyAML6.sock doesn’t exist
gpsd:PROG: KPPS:/dev/ttyAML6 checking /sys/devices/virtual/pps/pps0/path, /dev/ttyAML6
gpsd:INFO: KPPS:/dev/ttyAML6 RFC2783 path:/dev/pps0, fd is 6
gpsd:INFO: KPPS:/dev/ttyAML6 pps_caps 0x1133
gpsd:INFO: KPPS:/dev/ttyAML6 have PPS_CANWAIT
gpsd:INFO: KPPS:/dev/ttyAML6 kernel PPS will be used
gpsd:PROG: PPS:/dev/ttyAML6 thread launched
gpsd:INFO: PPS: activated /dev/ttyAML6 ntpshm_link_activate(): Clock
gpsd:INFO: KPPS:/dev/ttyAML6 kernel PPS timeout unknown error
gpsd:INFO: KPPS:/dev/ttyAML6 kernel PPS timeout unknown error
gpsd:INFO: KPPS:/dev/ttyAML6 kernel PPS timeout unknown error
gpsd:INFO: running with effective group ID 20
gpsd:INFO: running with effective user ID 115

pps is still not received by gpsd. Don’t know why. I’ve modded the python gpio getter script to sample 20 times a second for 5 seconds. (sudo python3 mygpioget.py 1 93) chip1-93 is the cts pin 12. You can see the 100 ms pulses are there, -

pi@libre-two:~/gpio $ sudo python3 mygpioget.py 1 93
0011000000000000000000110000000000000000011000000000000000000110000000000000000001100000000000000000

Gpsd does receive the serial messages from the gps on uarta and can generate the time, but no pps. Gpsd monitors RI, CD and CTS for pulses, not sure why there is a disconnect.

So that is it, I’ve used “sudo stty -F /dev/ttyAML6 crtscts” to turn on hardware flow control for the uart as well but no joy.

So I’m back to looking to enable a gpio pin with an interrupt to setup a pps-gpio device at /dev/pps0. Going to look at the existing overlays for a pin with an interrupt and try temp merging them to see if the pps pulses generate the interrups required on the pin.

14

It clearly indicates the problem. You have to specify the interrupt explicitly in the device tree overlay. You cannot assume the platform can figure out which IRQ it is based on the GPIO as this platform has no gpio_to_irq function. There are other overlays with interrupts and you can copy them verbatim as long as the interrupt controller is correct and the interrupt line number is correct.

15

Here is my latest attempt, still no joy. dmesg error here -

[   57.774241] pps-gpio 0.pps: error -ENOENT: failed to request PPS GPIO
[   57.774266] pps-gpio: probe of 0.pps failed with error -2


//setup pps-gpio on pin 11, chip0-pin8 -- GPIOAO_8

/dts-v1/;
/plugin/;

#include "dt-bindings/gpio/gpio.h"
#include "dt-bindings/gpio/meson-gxl-gpio.h"
#include "dt-bindings/interrupt-controller/irq.h"
#include "meson-gic.h"

/ {
        compatible = "libretech,cc", "amlogic,s905x", "amlogic,meson-gxl";


                fragment@0 {
                  target-path = "/";            
                __overlay__ {

                        pps: pps@0 {
                                compatible = "pps-gpio";
                                reg = <0>;
                                interrupt-parent = <&gpio_intc>;
                                interrupts = <MESON_GIC_GXL_GPIOAO_8 IRQ_TYPE_EDGE_RISING>;
                                pps-gpio = <&gpio_ao GPIOAO_8 GPIO_ACTIVE_HIGH>;
                                status = "okay";
                        };
                };
        };
};
dmesg gives -
16

At this point think I can say pps-gpio is not compatible with a le potato. If you need a precision ntp server with pps discipline you will need to find another soc.

17

Just took a look at the pps-gpio driver. It uses the gpiod_to_irq function exclusively and does not look for interrupts. As this platform does not have a gpiod_to_irq function, it’s unable to grab the right interrupt.

This will require a kernel patch to add feeding the interrupt directly to the driver instead of the driver failing to map a GPIO to interrupt. We have added this to our engineering task list.

18

You need to install our GPIO to IRQ enabled kernel:

sudo apt update
sudo apt install linux-image-6.1.y-lts-irq-arm64

Then use this overlay: libretech-wiring-tool/pps-gpio-7j1-12.dts at master · libre-computer-project/libretech-wiring-tool · GitHub

19

Thank you! I’ve updated with the modded kernel and applied the overlay and am getting the time pulses recognized.

One issue with the overlay, think … IRQ_TYPE_EDGE_FALLING>;
assert-falling-edge; …
both FALLING/falling should be RISING/rising as the rising edge of the time pulse corresponds to the start of the second. That is the only change I’ve made. Need to do more testing and get the Chrony configuration sorted for the best operation. Hope to get out a post soon with the working setup for everything.

20

Please test it and report any changes needed to the overlay. We have emables GPIO to IRQ on our standard LTS kernel.