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147 lines
5.1 KiB
Markdown
147 lines
5.1 KiB
Markdown
# PPS Time Synchronization (PX4 Integration)
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[Pulse Per Second](https://en.wikipedia.org/wiki/Pulse-per-second_signal) (PPS) time synchronization provides high-precision timing for GNSS receivers.
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This page explains how PPS is integrated into PX4 and how to configure it.
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## 개요
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PPS (Pulse Per Second) is a timing signal provided by GNSS receivers that outputs an electrical pulse once per second, synchronized to UTC time.
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The PPS signal provides a highly accurate timing reference that PX4 can use to:
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- Refine GNSS time measurements and compensate for clock drift
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- Provide precise UTC timestamps for camera capture events (for photogrammetry and mapping applications)
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- Enable offline position refinement through accurate time correlation
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## 지원 하드웨어
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PPS time synchronization can be supported on flight controllers that have a hardware timer input pin that can be configured for PPS capture, by [enabling the PPS capture driver](#enable-pps-driver-in-board-configuration) in the board configuration.
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Supported boards include (at time of writing):
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- [Ark FMUv6x](../flight_controller/ark_v6x.md)
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- Auterion FMUv6x
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- Auterion FMUv6s
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## 설정
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### Enable PPS Driver in Board Configuration
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The [PPS capture driver](../modules/modules_driver.md#pps-capture) must be enabled in the board configuration.
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This is done by adding the following to your board's configuration:
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```ini
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CONFIG_DRIVERS_PPS_CAPTURE=y
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```
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### Configure PPS Parameters
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The configuration varies depending on your flight controller hardware.
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#### FMUv6X
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For FMUv6X-based flight controllers, configure PWM AUX Timer 3 and Function 9:
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```sh
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param set PWM_AUX_TIM3 -2
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param set PWM_AUX_FUNC9 2064
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param set PPS_CAP_ENABLE 1
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```
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#### FMUv6S
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For FMUv6S-based flight controllers, configure PWM MAIN Timer 3 and Function 10:
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```sh
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param set PWM_MAIN_TIM3 -2
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param set PWM_MAIN_FUNC10 2064
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param set PPS_CAP_ENABLE 1
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```
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#### Multi-GPS Setups
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If you have multiple GPS receivers, set `PPS_CAP_GPS_ID` to the device ID of the GPS receiver that emits the PPS signal.
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When set to `0` (default), the driver uses the first available GPS instance.
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You can find the device ID by running:
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```sh
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listener sensor_gps
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```
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### 배선
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The wiring configuration depends on your specific flight controller.
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#### Skynode X (FMUv6x)
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Connect the PPS signal from your GNSS module to the flight controller using the 11-pin or 6-pin GPS connector:
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For detailed pinout information, refer to:
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- [Skynode GPS Peripherals - Pinouts](https://docs.auterion.com/hardware-integration/skynode/peripherals/gps#pinouts)
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#### Skynode S (FMUv6S)
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For FMUv6S, you need to route the PPS signal separately:
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1. Connect your GNSS module using the standard 6-pin GPS connector: [Skynode S GPS Interface](https://docs.auterion.com/hardware-integration/skynode-s/interfaces#gps)
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2. Connect the PPS signal from your GNSS module to the **PPM_IN** pin: [Skynode S Extras 1 Interface](https://docs.auterion.com/hardware-integration/skynode-s/interfaces#extras-1)
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#### ARK Jetson Carrier Board (FMUv6x)
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For ARK FMUv6X on the Jetson carrier board:
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1. Connect your GNSS module using either the 10-pin or 6-pin GPS connector: [ARK PAB GPS1 Interface](../flight_controller/ark_pab.md#gps1)
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2. Connect the PPS signal to the **FMU_CAP** pin: [ARK PAB ADIO Interface](../flight_controller/ark_pab.md#adio)
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## 검증
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After configuring PPS, you can verify that it is working correctly:
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1. Connect to the [PX4 System Console](../debug/system_console.md) (via MAVLink shell or serial console).
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2. Wait for GNSS fix.
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3. Check the PPS capture status to confirm it is up and running:
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```sh
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pps_capture status
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```
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4. You can also check the [PpsCapture](../msg_docs/PpsCapture.md) uORB topic
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```sh
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listener pps_capture
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```
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Where you should see: `timestamp`, `rtc_timestamp`, and `pps_rate_exceeded_counter`.
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### PPS Capture Driver
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The PPS capture driver is located in `src/drivers/pps_capture` and uses hardware timer input capture to precisely measure the arrival time of each PPS pulse.
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주요 기능:
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- Sub-microsecond pulse capture precision (hardware-dependent)
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- Automatic drift calculation and compensation
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- Integration with the GNSS driver for refined time stamping
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See also:
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- [PPS Capture Driver Documentation](../modules/modules_driver.md#pps-capture)
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- [PpsCapture Message](../msg_docs/PpsCapture.md)
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### Time Synchronization Flow
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1. GNSS module sends position/time data at ~1-20 Hz.
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2. GNSS module outputs PPS pulse at 1 Hz, precisely aligned to UTC second boundary.
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3. PPS capture driver measures the exact time of the PPS pulse arrival using hardware timer.
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4. Driver calculates the offset between GNSS time (from UART data) and autopilot clock (from PPS measurement).
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5. This offset is used to correct GNSS timestamps and improve sensor fusion accuracy.
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The PPS signal provides much higher temporal precision than the transmitted time data, which has latency and jitter from serial communication.
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:::warning
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If the PPS driver does not send any data for 5 seconds (despite having `PPS_CAP_ENABLE` set to 1), the corresponding `SENS_GPS*_DELAY` parameter will be used instead for estimating the latency.
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:::
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