WIP samples: drivers: nrf_timer: assess drift with 1pps signal

Track time using the system timer, SysTick, and a TIMER peripheral,
capturing at external 1pps signals and estimating error.

When HFCLK is on the timer and systick errors are less than 1 ppm.  In
that case synth is the highest accuracy LFCLK source, with XTAL then
RC in decreasing accuracy.

When HFCLK is off the timer and systick errors are the same and are
generally between 3000 and 4000 ppm.  Using the synth clock LFCLK
tracks the HFCLK error; RC reduces to between -30 and -60 ppm (30 ppm
resolution); XTAL between 0 and 30 ppm (longer samples show 25 ppm).

Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>

Author: pabigot

samples/drivers/nrf_timer/CMakeLists.txt

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+# SPDX-License-Identifier: Apache-2.0
+
+cmake_minimum_required(VERSION 3.13.1)
+find_package(Zephyr HINTS $ENV{ZEPHYR_BASE})
+project(NONE)
+
+FILE(GLOB app_sources src/*.c)
+target_sources(app PRIVATE ${app_sources})

samples/drivers/nrf_timer/Kconfig

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+# Copyright (c) 2019 Peter Bigot Consulting, LLC
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+config APP_SET_ALIGNED_CLOCK
+	bool "Option to align RTC with time-since-boot"
+	help
+	  If enabled this reads the RTC then sets it so that uptime
+	  shows as being relative to the start of the next hour.
+
+source "Kconfig"

samples/drivers/nrf_timer/boards/nrf51dk_nrf51422.overlay

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+/*
+ * Copyright (c) 2019 Peter Bigot Consulting, LLC
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+&i2c0 { /* SDA 30, SCL 7 */
+	status = "okay";
+	ds3231: ds3231@68 {
+		compatible = "maxim,ds3231";
+		reg = <0x68>;
+		label = "DS3231";
+		isw-gpios = <&gpio0 0 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
+	};
+};

samples/drivers/nrf_timer/boards/nrf52840dk_nrf52840.overlay

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+/*
+ * Copyright (c) 2019 Peter Bigot Consulting, LLC
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+&i2c0 { /* SDA P0.26, SCL P0.27 */
+	status = "okay";
+	ds3231: ds3231@68 {
+		compatible = "maxim,ds3231";
+		reg = <0x68>;
+		label = "DS3231";
+		isw-gpios = <&gpio0 0 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
+	};
+};

samples/drivers/nrf_timer/boards/particle_xenon.overlay

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+/*
+ * Copyright (c) 2019 Peter Bigot Consulting, LLC
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+&i2c0 { /* SDA P0.26, SCL P0.27, ISW P1.1, 32K P1.2 */
+	status = "okay";
+	ds3231: ds3231@68 {
+		compatible = "maxim,ds3231";
+		reg = <0x68>;
+		label = "DS3231";
+		isw-gpios = <&gpio1 1 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
+		32k-gpios = <&gpio1 2 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
+	};
+};
+
+/ {
+  test-config {
+     compatible = "test,nrf-timer";
+     status = "okay";
+     tick-rtc = <&rtc1>;
+     hf-timer = <&timer0>;
+     int-gpios = <&gpio1 1 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
+     lf-gpios = <&gpio1 2 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
+     hf-gpios = <&gpio1 8 (GPIO_PULL_UP | GPIO_ACTIVE_LOW)>;
+  };
+};

samples/drivers/nrf_timer/dts/bindings/test,nrf-timer.yaml

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+#
+# Copyright (c) 2020 Nordic Semiconductor ASA
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+
+description: |
+    This binding provides resources required to build and run the
+    samples/drivers/nrf_timer test.
+
+compatible: "test,nrf-timer"
+
+properties:
+    tick-rtc:
+      type: phandle
+      required: false
+      description: |
+        Reference to the RTC peripheral used as the system tick timer.
+        If absent uses NRF_RTC1 which is hard-coded as the tick timer.
+        CC[0] is by the tick timer for alarms; CC[1] is used by this
+        application for triggered capture.
+
+    hf-timer:
+      type: phandle
+      required: true
+      description: |
+        Reference to the TIMER peripheral used as the high-frequency
+        clock.  This timer must support 32-bit mode.  In this
+        application CC[0] is used to read the timer; CC[1] is used for
+        triggered capture.
+
+    int-gpios:
+        type: phandle-array
+        required: true
+        description: |
+          Identity of a GPIO that will be connected to the 1pps signal
+          and serve as the trigger for an interrupt in which the ticks
+          counter will be captured.
+
+    hf-gpios:
+        type: phandle-array
+        required: true
+        description: |
+          Identity of a GPIO that will be connected to the 1pps signal
+          and serve as the trigger for a GPIOTE input event connected to
+          an TIMER capture task.
+
+    lf-gpios:
+        type: phandle-array
+        required: true
+        description: |
+          Identity of a GPIO that will be connected to the 1pps signal
+          and serve as the trigger for a GPIOTE input event connected to
+          an RTC capture task.

samples/drivers/nrf_timer/prj.conf

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+CONFIG_PRINTK=y
+
+CONFIG_I2C=y
+CONFIG_COUNTER=y
+CONFIG_COUNTER_DS3231=y
+
+CONFIG_HWINFO=y
+CONFIG_CLOCK_CONTROL_NRF_K32SRC_XTAL=y
+CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC=n
+CONFIG_CLOCK_CONTROL_NRF_K32SRC_SYNTH=n

samples/drivers/nrf_timer/sample.yaml

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+sample:
+  description: DS3231 sample program
+  name: rtc_ds3231
+tests:
+  sample.driver.rtc_ds3231:
+    build_only: true
+    platform_whitelist: efr32mg_sltb004a frdm_k64f nrf51_pca10028 nucleo_l476rg particle_xenon