PPS on i.MX6Q IT

Technical Support
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1

I am using a Trimble Mini-T GNSS module which is connected to a custom carrier board with an Apalis iMX6Q module. I am trying to get the PPS from the GNSS to the Apalis module for accurate time. I have added these lines to my device tree

/ {
        ........
        pps {
             compatible = "pps-gpio";
             pinctrl-names = "default";
             pinctrl-0 = <&pinctrl_pps>;
             gpios = <&gpio2 4 GPIO_ACTIVE_HIGH>;
             status = "okay";
        };
};

&iomuxc {
	pinctrl-names = "default";

        ........

	pinctrl_pps: pps {
		fsl,pins = <
			MX6QDL_PAD_NANDF_D4__GPIO2_IO04 0x130b0
		>;
	};
};

When i boot the module, it appears that the pps module is being created and assigned… well actually it looks like 3 of them are

root@acu3:~# dmesg |grep pps
[    0.238628] pps_core: LinuxPPS API ver. 1 registered
[    0.238632] pps_core: Software ver. 5.3.6 - Copyright 2005-2007 Rodolfo Giometti <giometti@linux.it>
[    0.471134] pps pps0: new PPS source ptp0
[    0.493930] pps_ldisc: PPS line discipline registered
[    0.494529] pps pps1: new PPS source pps.-1
[    0.494761] pps pps1: Registered IRQ 118 as PPS source
[   16.751466] pps pps2: new PPS source IMX-uart4
[   16.751554] pps pps2: source "/dev/ttymxc4" added

The GPS works perfectly using gpsd’s ‘cgps’ and when I scope the PCB trace, I can see the PPS signal so I know that it is reaching the pin. However when I run ‘ppstest’ I get nothing.

root@acu3:~# ppstest /dev/pps1
trying PPS source "/dev/pps1"
found PPS source "/dev/pps1"
ok, found 1 source(s), now start fetching data...
time_pps_fetch() error -1 (Connection timed out)
time_pps_fetch() error -1 (Connection timed out)
^C
root@acu3:~# ppstest /dev/pps0
trying PPS source "/dev/pps0"
found PPS source "/dev/pps0"
ok, found 1 source(s), now start fetching data...
time_pps_fetch() error -1 (Connection timed out)
time_pps_fetch() error -1 (Connection timed out)
^C
root@acu3:~# ppstest /dev/pps2
trying PPS source "/dev/pps2"
found PPS source "/dev/pps2"
ok, found 1 source(s), now start fetching data...
time_pps_fetch() error -1 (Connection timed out)
time_pps_fetch() error -1 (Connection timed out)
^C

Any thoughts as to what the issue might be. I am using ntpd for timing and it isnt working correctly but I feel that is due to the system not recognizing the PPS signal.

2

Which MXM pin you are using for PPS?

Could you share PPS related changes at kernel config you’ve made ?

3

@alex.tx the PPS signal is connected to MXM pin 1 (NAND_DATA04, GPIO2_IO4). I have not made any changes to the kernel config.

root@acu3:~# zcat /proc/config.gz | grep PPS
CONFIG_PPS=y
# CONFIG_PPS_DEBUG is not set
# PPS clients support
# CONFIG_PPS_CLIENT_KTIMER is not set
CONFIG_PPS_CLIENT_LDISC=y
CONFIG_PPS_CLIENT_GPIO=y
# PPS generators support

Do i need to enable these other two PPS config settings?

4

I’m not familiar with PPS but will try to reproduce your issue using signal generator instead of GPS module. Meanwhile - could you try enable CONFIG_PPS_CLIENT_KTIMER ?

5

@alex.tx I added CONFIG_PPS_CLIENT_KTIMER to the kernel config and now the ppstest is successful. I will let you know if this also solves the problem with ntpd

6

Thank you for the update. Please open another ticket if you have ntpd or some other issue.