Based on GPTP time synchronization (clock synchronization server) technology to facilitate intelligent driving applications
Based on GPTP time synchronization (clock synchronization server) technology to facilitate intelligent driving
applications , FlexRay or MOST bus for communication, if this architecture is adopted by vehicles equipped with L4/L5 automatic driving functions, the time synchronization between multiple cameras and lidars may not be accurate enough, resulting in image data and point cloud data If they do not match, the driving strategy on the cockpit domain controller display may not be synchronized with the prompt sound from the speaker, or the time delay for sensor collection and perception data to be transmitted to the autopilot domain controller does not meet the requirements, then there is no doubt that the L4/L5 automatic The vehicle with the driving function is only a demonstration car, and cannot truly realize the L4/L5 automatic driving function.
Therefore, the precise time synchronization of each node in the in-vehicle network is very important to realize the L4/L5 automatic driving function, and the communication based on the vehicle Ethernet as the backbone network has the time synchronization function, which can meet the requirements.
At this stage, the time synchronization function based on the vehicle Ethernet is based on the gPTP protocol. However, in practical applications, due to abnormal conditions and other reasons, the clock synchronization information disappears, which in turn interrupts the clock synchronization. How to quickly synchronize after the clock synchronization information is lost remains a problem. It is a key problem that the time synchronization function of the vehicle Ethernet needs to solve. In order to find out the improvement route of the time synchronization technology of the vehicle Ethernet, we searched the relevant patents of the time synchronization technology of the vehicle Ethernet in the national patent database. The company has applied for many patents related to time synchronization of automotive Ethernet. In China, among universities and research institutes, TJ University has applied for a patent for time synchronization of vehicle Ethernet.
The patent applied to the time synchronization correction method and device of the master clock and the slave clock. This patent provides a feasible solution for how to quickly synchronize the clock synchronization information based on the gPTP protocol after the loss. The specific points are:
After the slave clock receives the synchronization time message sent by the master clock, it calculates the clock offset between the master clock and the slave clock, and uses the clock offset to correct the clock offset of the slave clock but does not correct the clock frequency of the slave clock; when specified The clock offset and clock frequency offset corrections are performed synchronously after the time.
Take the preset FM time as the starting position, and track the clock frequency offset between the master clock and the slave clock within the preset time period, and track the trend of the clock frequency offset between the master clock and the slave clock Estimation;
for example: set the measurement duration according to the user's needs, assuming that the test duration from Ts_2 to Ts_k is experienced, and the master-slave clock is corrected during the test duration, the specific calculation formula is as follows: Among them, in formula (1), Offset_i is the ith
time , where, i is calculated from the second time; in formula (2), Offset_total is the clock offset of all master and slave clocks within the preset period from Ts_2 to Ts_k.
Therefore, according to formulas (1) to formulas (4), the clock frequency of the slave clock is corrected by calculating the correction result of the clock frequency, so that the master clock and the slave clock maintain precise clock synchronization.
According to the measured data provided by a technology patent, the time synchronization correction method of HigPTP is compared with the clock synchronization correction method of LinuxPTP in the prior art, as shown in Figure 2. The results show that after 10 minutes using the LinuxPTP method, the clock The offset is changed from the initial 31477ns to 95344ns, the difference is 95344ns/10min, which is 99.8nm/s when converted into seconds. However, when the HigPTP method is used, after 10 minutes, the clock offset changes from the initial 31044ns to 23243ns. Compared with the LinuxPTP method, the time difference is reduced to 7801ns/10min, which is only 13nm/s when converted into seconds. The accuracy of clock synchronization Increased by about 8 times. Therefore, after HigPTP time synchronization, the time synchronization accuracy of the master clock and the slave clock is greatly improved compared with the existing technology.
Figure 2 Comparison of the calibration results of the master clock and slave clock using the HigPTP method provided by a certain technology and the existing LinuxPTP method
According to the above introduction, it can be known that many institutions and enterprises at home and abroad are still focusing on the precise time synchronization technology research of vehicle Ethernet. The centralized regional gateway architecture shown in Figure 3 adopts the time synchronization solution of vehicle Ethernet. It is a HigPTP scheme. It can be seen that the autopilot domain controller is used as the master clock. According to the master clock, the HigPTP scheme is used to synchronize the clocks of the vehicle Ethernet camera and the vehicle Ethernet lidar, and at the same time, synchronize the clock of the TSN gateway. Since the TSN gateway is connected to different domain controllers through the vehicle-mounted Ethernet bus, the TSN gateway is selected as the master clock, and the clocks of the power domain controller, chassis domain controller, body domain controller, and cockpit domain controller are accurately controlled through HigPTP. Synchronize. Through the clock synchronization method of HigPTP, the precise clock synchronization of each node of the vehicle Ethernet as the backbone network can be completed.
Figure 3 The precise clock synchronization technology solution based on the vehicle Ethernet as the backbone network.
If the self-driving vehicle equipped with L4/L5 adopts the HigPTP solution, due to the precise time synchronization function, the clock of the vehicle Ethernet laser radar and the vehicle Ethernet camera It can be accurately synchronized, so that point cloud data and image data can be collected synchronously and matched accurately. The delay in transmitting the sensory data collected by the sensor to the autonomous driving domain controller can be controlled, and the prompt sound played by the cockpit controller can always be synchronized with the content displayed on the screen, so the vehicle with the L4/L5 autonomous driving function becomes truly capable Autopilot vehicles.
It can be seen that in-vehicle Ethernet is very important for functions such as automotive intelligent network connection, ADAS, smart cockpit, and automatic driving. Fortunately, there are already many excellent high-tech companies in China that are engaged in related research and mass production of supporting products. , with the continuous advancement of the intelligentization of automobiles, it is believed that in the near future, the supporting products with the vehicle Ethernet bus as the backbone network will surely spread in the wave of intelligentization of automobiles.