NPL54 Timestamp Mechanism

The Timestamp

Our best practice for sensor fusion is to leverage the GPS PPS input to synchronize the LiDAR (via LiDAR encoder) and the GMSL2 camera (via frame sync, also known as FSYNC). The GPS PPS signal is a standard output from GPS modules, originating from satellites. "PPS" stands for "Pulse Per Second."

In general, most mechanical LiDARs support alignment to the GPS PPS input to mark the zero-degree position. The PCIe-NPL54 also ensures that camera frame sync is aligned with the GPS PPS input. The capability to apply a phase shift to the frame sync signal derived from the PPS input is currently available as an OEM feature.

If the customer prefers to use timestamps, the most accurate one would be based on the GPS PPS input, which can be obtained from a host computer via a GPS PPS module.

For the PCIe-NPL54, the earliest available timestamp is the "Start of Frame" from the FPGA (MIPI interface) on the NPL54. However, due to the camera's dynamic exposure time, the delay between the frame sync signal and the Start of Frame is not fixed.

---

Enable Timestamp

Please uncomment #define ENABLE_TIMESTAMP in NPL54Capture.cpp

...
#include "ConfigManager.h"
#include <thread>

#define ENABLE_TIMESTAMP

#ifndef ENABLE_TIMESTAMP                     // No Timestamp
#define VDMA_UPDATE_IDX_TIMEOUT 200          // Channel Level: Maximum timeout (in ms) to wait for a new valid frame
#define VDMA_UPDATE_IDX_TIMEOUT_ELSE_COUNT 1 // VDMA_UPDATE_IDX_TIMEOUT * VDMA_UPDATE_IDX_TIMEOUT_ELSE_COUNT > 200
#define MAX_TIMEOUT 5                        // Channel Level: The number of timeouts reported before issuing a retry
...

Then reinstall the npl54.service by ...

# In case you have previously installed NPL54
sudo systemctl stop npl54.service

cd NPL54_ES3/
# Please ensure you have Internet connected
sudo ./00_install_es3.sh

---

Using Timestamp

The timestamp is stored in the tv_sec and tv_usec fields of the timestamp member in the v4l2_buffer structure.

struct v4l2_buffer {
    ...
    struct timeval timestamp; // 
    ...
};

struct timeval {
    time_t      tv_sec;   // seconds since the Epoch (Jan 1, 1970)
    suseconds_t tv_usec;  // microseconds (0 to 999999)
};

---

Timestamp Example

4x AC-IMX490 | 20FPS Frmae | +25 %Phase Shift

Port	Epoch	                Gap (ms)
Port#0	1754370361167140023	
Port#1	1754370361179670750	12.52992
Port#2	1754370361192150683	12.48
Port#3	1754370361204662450	12.509952
Port#0	1754370361217142597	12.48
Port#1	1754370361229673443	12.52992
Port#2	1754370361242153310	12.48
Port#3	1754370361254665097	12.510208
Port#0	1754370361267145303	12.48
Port#1	1754370361279676077	12.52992
Port#2	1754370361292155817	12.48
Port#3	1754370361304667583	12.509952
Port#0	1754370361317148003	12.48
Port#1	1754370361329678777	12.52992
Port#2	1754370361342158423	12.48
Port#3	1754370361354670217	12.520192
Port#0	1754370361367183943	12.509952
Port#1	1754370361379681343	12.499968
Port#2	1754370361392161057	12.48
Port#3	1754370361404672837	12.509952
Port#0	1754370361417186643	12.509952
Port#1	1754370361429684037	12.500224
Port#2	1754370361442163690	12.48
Port#3	1754370361454675477	12.509952
Port#0	1754370361467189350	12.509952
Port#1	1754370361479686737	12.499968
Port#2	1754370361492166170	12.48
Port#3	1754370361504678097	12.509952
Port#0	1754370361517191950	12.519936
Port#1	1754370361529689310	12.489984
Port#2	1754370361542168803	12.48
Port#3	1754370361554680590	12.520192
Port#0	1754370361567194637	12.509952
Port#1	1754370361579692023	12.499968
Port#2	1754370361592171423	12.48
Port#3	1754370361604683210	12.509952
Port#0	1754370361617197343	12.509952
Port#1	1754370361629694610	12.500224
Port#2	1754370361642174063	12.48
Port#3	1754370361654685857	12.509952
Port#0	1754370361667199923	12.509952
Port#1	1754370361679697317	12.499968
Port#2	1754370361692176557	12.48
Port#3	1754370361704688470	12.509952
Port#0	1754370361717202610	12.519936
Port#1	1754370361729700030	12.500224
Port#2	1754370361742179170	12.470016
Port#3	1754370361754691110	12.519936
Port#0	1754370361767205310	12.509952
Port#1	1754370361779702603	12.499968
Port#2	1754370361792181797	12.48
Port#3	1754370361804693603	12.509952
Port#0	1754370361817208030	12.510208
Port#1	1754370361829705310	12.499968
Port#2	1754370361842184283	12.48
Port#3	1754370361854696223	12.509952
Port#0	1754370361867210610	12.519936
Port#1	1754370361879707910	12.489984
Port#2	1754370361892186923	12.48
Port#3	1754370361904698863	12.509952
Port#0	1754370361917213303	12.520192
Port#1	1754370361929710610	12.499968
Port#2	1754370361942189543	12.470016
Port#3	1754370361954701357	12.519936
Port#0	1754370361967216003	12.509952
Port#1	1754370361979713303	12.499968
Port#2	1754370361992192163	12.48
Port#3	1754370362004703977	12.509952
Port#0	1754370362017218583	12.510208
Port#1	1754370362029715890	12.499968
Port#2	1754370362042194657	12.48
Port#3	1754370362054706617	12.509952
Port#0	1754370362067221277	12.519936
Port#1	1754370362079718650	12.489984
Port#2	1754370362092197290	12.48
Port#3	1754370362104709230	12.509952
Port#0	1754370362117224003	12.520192
Port#1	1754370362129721350	12.499968
Port#2	1754370362142233143	12.509952
Port#3	1754370362154711870	12.48
Port#0	1754370362167226697	12.509952
Port#1	1754370362179723910	12.499968
Port#2	1754370362192235777	12.509952
Port#3	1754370362204714317	12.48
Port#0	1754370362217229270	12.510208
Port#1	1754370362229726603	12.499968
Port#2	1754370362242238403	12.509952
Port#3	1754370362254716930	12.48
Port#0	1754370362267231970	12.519936
Port#1	1754370362279729183	12.489984
Port#2	1754370362292241023	12.519936
Port#3	1754370362304719563	12.470016
Port#0	1754370362317234670	12.520192
Port#1	1754370362329731877	12.499968
Port#2	1754370362342243517	12.509952
Port#3	1754370362354722190	12.48
Port#0	1754370362367237243	12.509952
Port#1	1754370362379734457	12.499968
Port#2	1754370362392246150	12.510208
Port#3	1754370362404724683	12.48
Port#0	1754370362417239963	12.509952
Port#1	1754370362429737170	12.499968
Port#2	1754370362442248777	12.509952
Port#3	1754370362454727317	12.48
Port#0	1754370362467242663	12.519936
Port#1	1754370362479739743	12.489984
Port#2	1754370362492251397	12.520192
Port#3	1754370362504729937	12.46976
Port#0	1754370362517245357	12.520192
Port#1	1754370362529742450	12.499968
Port#2	1754370362542253890	12.509952
Port#3	1754370362554732557	12.48
Port#0	1754370362567247937	12.509952
Port#1	1754370362579745163	12.499968
Port#2	1754370362592256530	12.510208
Port#3	1754370362604735063	12.48