硬件设计

        GNSS模块输出pps到CPU，1PPS_1.8V用于V2X的pps，GPIO35_1.8V用于pps-gpio。这里做了pps一分二，由于距离太近不影响功能，焊接R35 0欧电阻。

 驱动配置

		gps_pps_pins:ublox_gps@2 {
				leadcore,pins = "gpio34";
				leadcore,function = "gpio";
				leadcore,pull = <MUXPIN_PULL_DISABLE>;
		};

		gps_pps2_pins:pps_gpio@0 {
				leadcore,pins = "gpio35";
				leadcore,function = "gpio";
				leadcore,pull = <MUXPIN_PULL_DISABLE>;
		};

        ublox_gps {
            compatible = "morningcore,ublox-gps";
            //gps_d1v8_ctrl = <&gpio 255 0>;
            gps_rst = <&gpio 255 0>;
            gps_pps = <&gpio 34 0>;
            pinctrl-names = "d1v8_ctrl_pins", "rst_pin", "pps_pins";
            pinctrl-0 = <&gps_d1v8_ctrl_pins>;
            pinctrl-1 = <&gps_rst_pins>;
            pinctrl-2 = <&gps_pps_pins>;
        };

        pps_gpio {
            compatible = "morningcore,pps-gpio";
            gps_pps2 = <&gpio 35 0>;
            pinctrl-names = "pps2_pins";
            pinctrl-0 = <&gps_pps2_pins>;
        };

drivers/comip/wireless/ublox-gps.c
{ .compatible = "morningcore,ublox-gps", },
    comip_mfp_config(MFP_PIN_GPIO(34), MFP_PIN_MODE_GPIO);
    pdata->gpio_pps = of_get_named_gpio(pdev->dev.of_node, "gps_pps", 0);
    if (pdata->gpio_pps < 0) {
        dev_err(&pdev->dev, "get gps_pps failed\n");
        return -EINVAL;
    }
    gpio_request(pdata->gpio_pps, "GPS pps GPIO");
    gpio_direction_input(pdata->gpio_pps);
    comip_mfp_config_pull(pdata->gpio_pps, MFP_PULL_DISABLE);
    gpio_free(pdata->gpio_pps);

        调试发现gpio34如果没有配置不响应v2x功能，这是为何？

drivers/pps/clients/pps-gpio.c
{ .compatible = "morningcore,pps-gpio", },
    pdata->gpio_pin = of_get_named_gpio(pdev->dev.of_node, "gps_pps2", 0);
    //printk("wzl-debug pdata->gpio_pin=%d\n", pdata->gpio_pin);
    if (pdata->gpio_pin < 0) {
        dev_err(&pdev->dev, "get gps_pps2 failed\n");
        return -EINVAL;
    }

    comip_mfp_config1(pdata->gpio_pin, MFP_PIN_MODE_GPIO);

    /* IRQ setup */
    irq = gpio_to_irq(pdata->gpio_pin);
    if (irq < 0) {
        pr_err("failed to map GPIO to IRQ: %d\n", irq);
        err = -EINVAL;
        goto return_error;
    }

    ret = gpio_request(pdata->gpio_pin, "GPS pps2 GPIO");
    if (ret) {
        pr_warning("failed to request GPIO %u\n", pdata->gpio_pin);
        return -EINVAL;
    }

    ret = gpio_direction_input(pdata->gpio_pin);
    if (ret) {
        pr_warning("failed to set pin direction\n");
        gpio_free(pdata->gpio_pin);
        return -EINVAL;
    }
    comip_mfp_config_pull(pdata->gpio_pin, MFP_PULL_DISABLE);
    gpio_free(pdata->gpio_pin);

    /* register IRQ interrupt handler */
    ret = request_irq(irq, pps_gpio_irq_handler,
            IRQF_TRIGGER_RISING, data->info.name, data);
    if (ret) {
        pps_unregister_source(data->pps);
        pr_err("failed to acquire IRQ %d\n", irq);
        err = -EINVAL;
        goto return_error;
    }

static irqreturn_t pps_gpio_irq_handler(int irq, void *data)
{
    const struct pps_gpio_device_data *info;
    struct pps_event_time ts;
    int rising_edge;

    disable_irq_nosync(irq);

    /* Get the time stamp first */
    pps_get_ts(&ts);

    info = data;

    rising_edge = gpio_get_value(info->pdata->gpio_pin);
    //printk("wzl-debug:pps_gpio_irq_handler rising_edge = %d\n", rising_edge);
    if ((rising_edge && !info->pdata->assert_falling_edge) ||
            (!rising_edge && info->pdata->assert_falling_edge))
        pps_event(info->pps, &ts, PPS_CAPTUREASSERT, NULL);
    else if (info->pdata->capture_clear &&
            ((rising_edge && info->pdata->assert_falling_edge) ||
             (!rising_edge && !info->pdata->assert_falling_edge)))
        pps_event(info->pps, &ts, PPS_CAPTURECLEAR, NULL);

    enable_irq(irq);

    return IRQ_HANDLED;
}

        打开驱动配置：

#
# PPS support
#
CONFIG_PPS=y
CONFIG_PPS_DEBUG=y

#
# PPS clients support
#
# CONFIG_PPS_CLIENT_KTIMER is not set
# CONFIG_PPS_CLIENT_LDISC is not set
CONFIG_PPS_CLIENT_GPIO=y

        启动时内核打印和pps设备节点信息：

linux_genvict:~# dmesg | grep pps
[    0.303184]{0} pps_core: LinuxPPS API ver. 1 registered
[    0.303191]{0} pps_core: Software ver. 5.3.6 - Copyright 2005-2007 Rodolfo Giometti <giometti@linux.it>
[    3.534376]{1} pps_core: source pps_gpio.7.-1 got cdev (252:0)
[    3.534387]{1} pps pps0: new PPS source pps_gpio.7.-1
[    3.540090]{1} pps pps0: Registered IRQ 195 as PPS source

linux_genvict:~# ls /dev/pps0 -l
crw-rw----    1 root     0         252,   0 Jan  1 00:08 /dev/pps0

应用编译

        使用Buildroot 2017.02.3源码，选择外部编译链，编译gpsd、pps和chrony工具：

Target packages  --->
	Hardware handling  --->
		[*] gpsd  ----
			(/dev/ttyS1) Where to look for GPSes (NEW)
			[*]   client debugging support (NEW)
			[*]   profiling support (NEW)
			[*]   NTP time hinting support (NEW) 
			[*]   PPS time syncing support (NEW) 
			[*]   allow gpsd to change device settings (NEW)
			[*]   allow gpsctl/gpsmon to change device settings (NEW)
			[*]   NMEA (NEW)
		[*] pps-tools
	Networking applications  --->
		[*] chrony

[wangyb@wangyb-VirtualBox:target]$ find ./ -name gps*
./usr/sbin/gpsd
./usr/sbin/gpsdctl
./usr/bin/gpspipe
./usr/bin/gpsdecode
./usr/bin/gpsctl
./usr/bin/gpsmon
./usr/bin/gps2udp
[wangyb@wangyb-VirtualBox:target]$ find ./ -name pps*
./usr/bin/ppstest
./usr/bin/ppsfind
./usr/bin/ppswatch
./usr/bin/ppsctl
[wangyb@wangyb-VirtualBox:target]$ find ./ -name chrony*
./var/lib/chrony
./usr/sbin/chronyd
./usr/bin/chronyc

[wangyb@wangyb-VirtualBox:target]$ readelf -d ./usr/sbin/gpsd

Dynamic section at offset 0x25820 contains 29 entries:
  标记        类型                         名称/值
 0x00000001 (NEEDED)                     共享库：[libusb-1.0.so.0]
 0x00000001 (NEEDED)                     共享库：[libm.so.6]
 0x00000001 (NEEDED)                     共享库：[librt.so.1]
 0x00000001 (NEEDED)                     共享库：[libdbus-1.so.3]
 0x00000001 (NEEDED)                     共享库：[libpthread.so.0]
 0x00000001 (NEEDED)                     共享库：[libc.so.6]

测试pps

        R35电路没有焊接的情况下：

linux_genvict:/data/upgrade# ./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)
time_pps_fetch() error -1 (Connection timed out)
time_pps_fetch() error -1 (Connection timed out)

        短接R35电阻，pps接在gpio35：

linux_genvict:/data/upgrade# ./ppstest /dev/pps0 
trying PPS source "/dev/pps0"
found PPS source "/dev/pps0"
ok, found 1 source(s), now start fetching data...
source 0 - assert 1686797890.917627372, sequence: 88 - clear  0.000000000, sequence: 0
source 0 - assert 1686797891.917628603, sequence: 89 - clear  0.000000000, sequence: 0
source 0 - assert 1686797892.917629680, sequence: 90 - clear  0.000000000, sequence: 0
source 0 - assert 1686797893.917603988, sequence: 91 - clear  0.000000000, sequence: 0
source 0 - assert 1686797894.917600834, sequence: 92 - clear  0.000000000, sequence: 0
source 0 - assert 1686797895.917604911, sequence: 93 - clear  0.000000000, sequence: 0
source 0 - assert 1686797896.917607372, sequence: 94 - clear  0.000000000, sequence: 0

        gpsd不使用pps：./gpsd -n -G /dev/ttygnss1

         gpsd使用pps：./gpsd -n -G /dev/ttygnss1 /dev/pps0 

 chrony校时

        添加chrony配置文件：/system/etc/chrony.conf

makestep 0.1 3
rtcsync
allow
leapsectz right/UTC
driftfile /var/lib/chrony/drift
dumpdir /var/run/chrony

refclock PPS /dev/pps0 refid PPS lock GPSD prefer precision 1e-7 poll 2
refclock SHM 0 refid GPSD precision 1e-1 offset 0.9999 delay 0.2 poll 2

        参考博客：嵌入式Linux 时间同步 gpsd+chrony_gpsd chrony_sep4075的博客-CSDN博客

        先运行gpsd，然后运行./chronyd -f /system/etc/chrony.conf：

         使用套接字方法让 chronyd 连接到 gpsd，添加配置：

refclock SOCK /var/run/chrony.ttygnss1.sock refid GPS precision 1e-1 offset 0.9999
refclock SOCK /var/run/chrony.pps0.sock refid PPS precision 1e-7