JP2015198399A - communication device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication device capable of achieving highly accurate time synchronization.SOLUTION: An initiator node 100 comprises a synchronization data transmission unit that transmits synchronization data and transmission time of the synchronization data to a Space Wire encoding unit 105 after stopping null transmission by the Space Wire encoding unit 105. A target node 200 comprises a time correction unit that corrects time of the target node 200 using the transmission time of the synchronization data, reception time of the synchronization data, and difference between transmission time and reception time in the state of the initiator node 100 synchronizing the target node 200 in terms of time.

Description

  The present invention mainly relates to a communication device that performs data communication such as a data processing device mounted on an artificial satellite.

  Conventionally, various communication methods such as the MIL-STD-1553B standard, RS422 or LVDS three-wire serial communication have been used for communication between data communication processing devices mounted on artificial satellites. Considering that such an unbalanced communication method is a factor leading to an increase in the cost of satellite development and a long development period, SpaceWire has been established as a communication standard aimed at unifying the communication method in the satellite. In the SpaceWire standard document shown in Non-Patent Document 1, a SpaceWire communication standard is defined, and from the physical layer to the network layer in the OSI reference model is determined as SpaceWire. SpaceWire is a full-duplex serial communication system, and transmits EOP (End of Packet), Time-Code, and NULL for maintaining a communication link, indicating the end of data in addition to normal data. Time-Code is data for the transmission side to send data to the target device on the network by broadcast. Since it cannot be put into the FIFO in each communication interface, it can be transmitted with a small delay time. Therefore, it is effective to use for time distribution, but the usage method is not defined by the standard.

  Each observation device needs to have a clock in order to keep track of natural phenomena and time. In addition, a device that controls the inside of an artificial satellite needs to have a clock that records changes in the state of the satellite. This clock is clocked by a counter with the TimePulse signal as a reference. These Time Pulses are generally generated when a certain counter and value are reached by a time counter that is counted up by an oscillator of each device. However, these oscillators, due to manufacturing variations among the oscillators and frequency changes due to temperature changes, shift the clock of each observation device after a long time, making it impossible to accurately record events. Therefore, there is a need for a method of synchronizing the time of all on-board devices centering on the satellite control computer. However, when SpaceWire is used as a network between devices, the satellite control computer transmits Time-Code, and each observation device transmits a Time-Code. A method is adopted in which a synchronization signal is generated at the reception timing of the code. Conventionally, as such a technique, for example, there has been a system in which a pulse is generated at the timing when a Time-Code is received and the timing is synchronized with time (see, for example, Patent Document 1). Non-Patent Document 2 shows how much delay occurs in the Time-Code when a device is connected via a router, and shows the cause of the analysis.

JP 2012-39349 A

SpaceWire standard "ECSS-E-ST-50-12C" M.M. Suses (2013), “SpaceWire Time-Code Latency and Jitter”, European Space Agency ESTEC, International SpaceWire Conference 2013

However, in the conventional system as described in Patent Document 1, a pulse is generated at the timing when the Time-Code is received to obtain the time synchronization timing, so that there is a problem that highly accurate time synchronization cannot be realized. there were. The reason is that when Time-Code is transmitted in a network on SpaceWire, there is a characteristic that fluctuation occurs probabilistically every time it is transmitted. This Time-Code fluctuation is caused by the protocol definition of SpaceWire and cannot be reduced.
In the configuration shown in FIG. 2, the SpaceWire encoding unit 105 and the SpaceWire decoding unit 201 perform serial communication, but the operation after the initialization of the SpaceWire data link performs communication by state transition as shown in FIG. The configuration in FIG. 2 will be described in Embodiment 1.

  In the case of SpaceWire, as shown in the flowchart of FIG. 6, NULL is transmitted when there is no data in the transmission FIFO 105a (step ST2: NO) or when there is no time-code transmission request (step ST1: NO). NULL requires 8 clocks to transmit 8 bits one clock at a time with 8 bits of data. During this NULL transmission, Time-Code and data cannot be transmitted. That is, when a Time-Code transmission request is made, the transmission waits from 0 clock to 8 clocks. The number of clocks to wait for is a uniform probability distribution. This waiting time causes fluctuations in Time-Code transmission. Further, when the devices are connected via one router, the number of SpaceWire encoding units is increased by one, so that two fluctuations are superimposed. As the number of routers increases, fluctuations overlap and become larger.

  Since the Time-Code is transmitted by broadcast, a plurality of devices receive the Time-Code, but the number of SpaceWire routers that pass through each device varies depending on the network topology of SpaceWire. For this reason, since the magnitude of the synchronization fluctuation is different for each device, the clock is shifted for each device.

  The present invention has been made to solve the above-described problems, and an object of the present invention is to obtain a communication apparatus capable of realizing highly accurate time synchronization.

  The communication device according to the present invention is a communication device composed of an initiator node and a target node connected by SpaceWire. The initiator node encodes a SpaceWire packet and transmits it to the target node, and a NULL of the SpaceWire encoding unit. A synchronization data transmission unit that transmits the synchronization data and the transmission time of the synchronization data to the SpaceWire encoding unit after the transmission is stopped, and the target node includes the transmission time of the synchronization data, the reception time of the synchronization data at the target node, and A time correction unit that corrects the time of the target node using the difference between the transmission time and the reception time when the target node and the initiator node are synchronized in time is provided.

  The communication device of the present invention transmits the synchronization data and the transmission time of the synchronization data to the target node after stopping the NULL transmission of the SpaceWire encoding unit, and synchronizes the transmission time with the reception time on the target node side. Since the time of the target node is corrected using the difference between the transmission time and the reception time in the case of being present, highly accurate time synchronization can be realized.

It is a block diagram which shows the communication apparatus by Embodiment 1 of this invention. It is a block diagram which shows the detail of the SpaceWire encoding part and SpaceWire decoding part of the communication apparatus by Embodiment 1 of this invention. It is explanatory drawing which shows the format of the SpaceWire packet of the communication apparatus by Embodiment 1 of this invention. It is a flowchart which shows operation | movement of the communication apparatus by Embodiment 1 of this invention. It is a timing chart which shows the time timing of the initiator node of the communication apparatus by Embodiment 1 of this invention, and a target node. It is explanatory drawing which shows the transmission process of Time-Code of the communication apparatus by Embodiment 1 of this invention, data, and NULL. It is a block diagram which shows the communication apparatus by Embodiment 2 of this invention. It is a block diagram which shows the communication apparatus by Embodiment 3 of this invention. It is a block diagram which shows the communication apparatus by Embodiment 4 of this invention.

Embodiment 1 FIG.
1 is a block diagram showing a communication apparatus according to Embodiment 1 of the present invention.
In the communication apparatus shown in FIG. 1, an initiator node 100 and a target node 200 are connected by a SpaceWire 300 to perform communication. The initiator node 100 is a master device that manages time, and the target node 200 is a slave device that is time-managed by the initiator node 100.

  The initiator node 100 includes a data transmission unit 101, a time generation unit 102, a synchronization start data transmission unit 103, a Time-Code transmission unit 104, and a SpaceWire encoding unit 105. The data transmission unit 101 is a processing unit that performs data transmission to the target node 200 as the initiator node 100. The time generation unit 102 is a processing unit that generates time data in the initiator node 100, and includes an oscillator 102a and a time counter 102b. The oscillator 102a is an oscillator that generates data of a predetermined frequency, and the time counter 102b is a counter that counts the transmission frequency from the oscillator 102a and outputs it as a clock. The synchronization start data transmission unit 103 is a processing unit that transmits synchronization start data for performing time synchronization with the target node 200, and includes a measurement counter unit 103a and a start data transmission unit 103b. The measurement counter unit 103a is a counter for counting the count value from the time generation unit 102 and detecting the transmission time of the synchronization data EOP, and the start data transmission unit 103b outputs the count value of the measurement counter unit 103a. Is a processing unit. The Time-Code transmission unit 104 is a processing unit that transmits the time of the time generation unit 102 and the synchronization data from the start data transmission unit 103b as Time-Code. The SpaceWire encoding unit 105 is a processing unit that encodes serial data as SpaceWire. The internal configuration of the SpaceWire encoding unit 105 will be described later. In addition, the data transmission unit 101 to the Time-Code transmission unit 104 constitute a synchronization data transmission unit that transmits the synchronization data and the transmission time of the synchronization data to the SpaceWire encoding unit 105 after the NULL transmission of the SpaceWire encoding unit 105 is stopped. ing.

  The target node 200 includes a SpaceWire decoding unit 201, a data decoding unit 202, a data receiving unit 203, a reset unit 204, a time generation unit 205, and a processing circuit unit 206. The SpaceWire decoding unit 201 is a processing unit that decodes a SpaceWire packet received from the initiator node 100 via the SpaceWire 300, and details thereof will be described later. The data decoding unit 202 is a processing unit that determines the start and end of the time synchronization operation based on the data decoded by the SpaceWire decoding unit 201. The data receiving unit 203 is a processing unit that receives data from the SpaceWire decoding unit 201 based on the STOP signal and the START signal from the data decoding unit 202. The reset unit 204 is a processing unit that waits for EOP based on the STOP signal from the data decoding unit 202 and sends this information to the time generation unit 205 when EOP is output from the SpaceWire decoding unit 201.

The time generation unit 205 is a processing unit that generates time in the target node 200, and includes an oscillator 205a, a measurement counter unit 205b, a delay correction unit 205c, a preset value 205d, and a time counter 205e. Here, the oscillator 205a and the time counter 205e are processing units for generating the time at the target node 200, similarly to the oscillator 102a and the time counter 102b in the time generation unit 102 of the initiator node 100. The measurement counter unit 205b is a counter for counting the EOP reception time based on the START signal from the reset unit 204 and the STOP signal from the time counter 205e. The delay correction unit 205c receives the EOP reception time counted by the measurement counter unit 205b, the difference between the transmission time and the reception time when the initiator node 100 and the target node 200 are time-synchronized. The processing unit calculates a delay correction value based on the EOP transmission time in the initiator node 100 received by the data receiving unit 203. The preset value 205d is a preset value when the time counter 205e counts, and is a value corrected by the delay correction unit 205c. The data decoding unit 202 to the time generation unit 205 constitute a time correction unit that corrects the time of the target node 200.
The processing circuit unit 206 is a circuit that performs various processes in the target node 200.

  FIG. 2 is a configuration diagram of the SpaceWire encoding unit 105 and the SpaceWire decoding unit 201. As illustrated, the SpaceWire encoding unit 105 includes a transmission FIFO 105a and a serialized transmission unit 105b. The transmission FIFO 105a is a first-in first-out memory that temporarily stores and transmits data. The serialization transmission unit 105b is a processing unit that serializes data from the Time-Code or the transmission FIFO 105a and outputs the data to the SpaceWire 300. The SpaceWire decoding unit 201 includes a parallelization reception unit 201a and a reception FIFO 201b. The parallel receiving unit 201a is a processing unit that outputs a serial packet from the SpaceWire 300 as parallel data, and the reception FIFO 201b is a first-in first-out memory that temporarily stores received data.

Next, the operation of the communication apparatus according to the first embodiment will be described.
The data transmission unit 101 sends DATA while monitoring the FULL signal of the SpaceWire encoding unit 105. Send EOP to the end of DATA. The SpaceWire encoding unit 105 converts the received 8-bit data into serial data, generates a signal according to the SpaceWire standard, and sends the signal to the target node 200. The SpaceWire decoding unit 201 of the target node 200 converts the serial data into parallel data by the parallelization receiving unit 201a, accumulates it in the reception FIFO 201b, and waits for the data receiving unit 203 to receive it. The data receiving unit 203 monitors the EMPTY signal from the SpaceWire decoding unit 201. When the EMPTY signal is deasserted, the data receiving unit 203 recognizes that data can be received and receives data from the SpaceWire decoding unit 201.

  The time counter 102b in the time generation unit 102 of the initiator node 100 indicates a reference time, and the time counter 205e of the time generation unit 205 of the target node 200 initially operates in synchronization with the time counter 102b of the initiator node 100. To do. The time counter 205e is counted up by the clock generated by the 50 MHz oscillator 205a, and when the value set in the preset value 205d is reached, Time_Pulse is generated and reset. Time_Pulse is used as a timing signal for driving the processing circuit unit 206 according to the schedule. When time elapses, a deviation occurs due to the inherent difference between the 50 MHz oscillator 102a and the 50 MHz oscillator 205a. In this embodiment, this deviation is corrected.

  In the configuration in which the initiator node 100 that operates based on the 50 MHz oscillator 102a and the target node 200 that also operates based on the 50 MHz oscillator 205a are connected by a 2 MHz SpaceWire 300, the initiator node 100 The time reference signal Time_Pulse and the time reference signal Time_Pulse of the target node 200 are matched. The frequency of the oscillator 102a and the oscillator 205a of the initiator node 100 and the target node 200 uses a device of 50 MHz. However, the time counter 102b and the time counter 205e are different from each other due to manufacturing variations and temperature changes. It will shift. Therefore, in order to make Time_Pulse the same timing again, the initiator node 100 transmits a SpaceWire packet 400 having a header 400a indicating the start of the synchronization operation to the target node 200. FIG. 3 shows the format of the SpaceWire packet 400. As illustrated, the SpaceWire packet 400 includes a header 400a, a data part 400b, and an end part (EOP) 400c.

  FIG. 4 is an explanatory diagram showing operations of the initiator node 100 and the target node 200. In FIG. 4, data with a synchronization start header is transmitted from the initiator node 100 in step ST11.

  After receiving the data, the target node 200 recognizes that the data decoding unit 202 decodes the header and starts the synchronization operation. At the start of the synchronization operation, a STOP signal is output to the data receiving unit 203 so that subsequent data is not received (step ST21). That is, data is not acquired even when the EMPTY signal of the SpaceWire decoding unit 201 becomes invalid and data can be acquired (step ST22). Further, the STOP signal is also output to the reset unit 204 to wait for EOP detection at the end of the SpaceWire packet of the data (step ST23).

  In this state, in the initiator node 100, the data transmission unit 101 continues to transmit the SpaceWire packet 400 to the SpaceWire encoding unit 105 (step ST12). When the FIFOs of the SpaceWire encoding unit 105 and the SpaceWire decoding unit 201 become full, the SpaceWire encoding unit 105 of the initiator node 100 outputs a FULL signal to the data transmission unit 101. As a result, the data transmission unit 101 stops data transmission and sets the next transmission data as EOP (step ST13).

Next, the synchronization start data transmission unit 103 of the initiator node 100 transmits 0xFF as the Time-Code to the target node 200 (step ST14).
When the target node 200 receives 0xFF as Time-Code, the data decoding unit 202 transmits a START signal to the data receiving unit 203. When receiving the START signal, the data receiving unit 203 continues to receive data from the SpaceWire decoding unit 201 (step ST24). The data reception unit 203 continues to receive data at a sufficiently high speed so that the reception FIFO 201b of the SpaceWire decoding unit 201 including a SpaceWire router (not shown) on the SpaceWire 300 is not full.

  The initiator node 100 transmits the data of the termination unit (EOP) 400c when the FULL signal of the transmission FIFO 105a is deasserted. The synchronization start data transmission unit 103 of the initiator node 100 measures the EOP transmission time T1 using the Time_Pulse from the time generation unit 102 as a START signal (step ST15). On the other hand, the time generation unit 205 of the target node 200 starts the Time_Pulse generated by the time counter 205e, and measures the EOP reception time T3 based on the EOP received by the reset unit 204 (step ST25). T3-T1 in a state where the Time_Pulse of the initiator node 100 and the target node 200 at the initial stage when the apparatus is configured is set as T2. T2 is used as a fixed value.

As time synchronization is lost, T3-T1 and T2 take different values. When the oscillator 205a on the target node 200 side is delayed, T3−T1 <T2, and when the oscillator 205a on the target node 200 side is fast, T3−T1> T2. The initiator node 100 transmits the value of T1 to the target node 200 by Time-Code (step ST16), and on the target node 200 side, the delay correction unit 205c calculates (T3-T1) -T2, and the result is a preset value. It is added only once to 205d (step ST26). When the time counter 205e reaches the corrected preset value 205d, it returns to 0, and the timing of Time_Pulse is corrected.
This is shown in the timing chart of FIG. In the illustrated example, since the timing on the target node 200 side is delayed by N-4, the timing of the preset value is corrected at the timing of N-4.

  As shown in FIG. 6, the SpaceWire encoding unit 105 proceeds with processing for each clock of a SpaceWire link rate of 2 MHz according to a flowchart for sending data, NULL, and Time-Code. In the conventional method of detecting Time-Code and generating Time_Pulse to synchronize, if data or NULL transmission is performed at the time of transmitting Time-Code, the transmission processing of Time-Code is awaited. . In the middle of data transmission, a maximum waiting time of 10 clocks and 5000 ns occurs. On the other hand, when the Time-Code is transmitted immediately after the NULL transmission or the data transmission is completed, the transmission can be performed without waiting time. Therefore, the accuracy when time synchronization is performed with Time-Code is 5000 ns.

  On the other hand, in the case of the present embodiment, there is a fluctuation in the EOP detection time because the SpaceWire decoding unit 201 asynchronously exchanges the data of SpaceWire and the data of the target node 200 with a clock of 50 MHz. This fluctuation is caused by fluctuation when the 50 MHz clock of the target node 200 is delayed by one clock and when it is not delayed, and therefore, fluctuation is 20 ns. In addition, asynchronous delivery of EOP between the SpaceWire encoding unit 105 and the initiator node 100 occurs. Since the timing at which the SpaceWire encoding unit 105 sends EOP is detected by sampling with the clock 50 MHz of the initiator node 100, a fluctuation of 20 ns occurs. Therefore, in the case of the present embodiment, time synchronization with an accuracy of 40 ns is realized. Therefore, compared with the accuracy of 5000 ns of the conventional configuration, the present embodiment realizes time synchronization with accuracy of 40 ns and realizes time synchronization with 125 times accuracy.

  Note that the initiator node 100 may temporarily transition to the time synchronization mode by the SpaceWire state transition, and stop the NULL transmission of the SpaceWire encoding unit 105. That is, in the communication device targeted by the present embodiment, the communication mode can be divided into a state (normal state) in which the user wants to transmit and receive data (sensor acquisition data and the like) and a time synchronization state. The time synchronization state is a state for temporarily synchronizing time, and transmission / reception of data that the user wants to transmit is interrupted. For the user, inconvenience is caused by not being able to send transmission / reception data, but without changing the specified SpaceWire protocol standard ECSS-E-ST-50-12C and for transmission / reception of the existing SpaceWire corresponding thereto Time synchronization can be performed without correcting the circuit logic.

  In addition, the initiator node 100 transmits data indicating a code for starting and stopping time synchronization other than the data format defined by SpaceWire, and the target node 200 side decodes this data to generate a time You may make it synchronize. That is, in addition to NULL (8-bit data) and Time-Code (14-bit data) of Control Codes already defined as “data other than the data format specified by SpaceWire”, the third, fourth new As Control Codes, codes for starting and stopping time synchronization (for example, time synchronization start parity (1110101) and stop parity (1110110)) are added, and the protocol is modified. When the SpaceWire decoding unit 201 receives this Control Codes, it outputs a signal corresponding to the START signal of the data decoding unit 202 to start time synchronization. In addition, when the SpaceWire decoding unit 201 receives the stop code, it outputs a signal corresponding to the STOP signal of the data decoding unit 202.

Further, the EOP transmission time may be transmitted from the initiator node 100 by a plurality of times-codes, and the target node 200 may perform the time correction operation with the accuracy of the bits received by the plurality of times-codes. .
For example, the Time-Code defined by SpaceWire (standard ECSS-E-ST-50-12C) can send data represented by 8 bits in one transmission. Here, if the time for one bit is 40 ns, it is 256 × 40 ns for 8 bits, and therefore, it is possible to correct the accuracy to 40 ns up to the maximum time shift of 10240 ns. Here, if one bit is set to 10 ns at the expense of the maximum time, the accuracy is improved. However, the maximum time can be corrected only up to a deviation of 2560 ns. Therefore, when the Time-Code is transmitted twice, 16-bit data can be transmitted, so that the maximum time shift of 655360 ns can be corrected with an accuracy of 10 ns.

  As described above, according to the communication device of the first embodiment, in a communication device composed of an initiator node and a target node connected by SpaceWire, the initiator node encodes the SpaceWire packet and transmits it to the target node. An encoding unit, and a synchronization data transmitting unit that transmits the synchronization data and the transmission time of the synchronization data to the SpaceWire encoding unit after stopping the NULL transmission of the SpaceWire encoding unit. A time correction unit that corrects the time of the local target node using the reception time of the data at the local target node and the difference between the transmission time and the reception time when the target node and the initiator node are in time synchronization. So equipped, it is possible to realize highly accurate time synchronization.

  Further, according to the communication apparatus of the second embodiment, the synchronization data transmission unit uses the SpaceWire packet including the header indicating the start of synchronization and the EOP (End of Packet) as the termination unit as the synchronization data, and the synchronization data transmission unit transmits the EOP. The time correction unit notifies the transmission time of the notified EOP, the reception time of the EOP, and the difference between the transmission time and the reception time when the target node and the initiator node are in time synchronization. Since the correction is performed by using the SpaceWire data, the SpaceWire data can be used as it is, and a specific target node can be selected to perform time synchronization.

  Further, according to the communication device of the first embodiment, the SpaceWire encoding unit includes a transmission FIFO, encodes the SpaceWire packet based on the data of the transmission FIFO, and the synchronous data transmission unit performs the following operations on the SpaceWire encoding unit: Since the NULL transmission is stopped by transmitting the amount of data that makes the transmission FIFO full, it is possible to realize highly accurate time synchronization without the need to modify the SpaceWire protocol.

  Also, according to the communication device of the first embodiment, the synchronous data transmission unit temporarily transits to the time synchronous mode by the state transition of SpaceWire and stops NULL transmission of the SpaceWire encoding unit, so the existing SpaceWire The time synchronization can be performed without correcting the transmission / reception circuit logic.

  Further, according to the communication device of the first embodiment, the synchronization data transmission unit transmits data with a header indicating the time synchronization operation, and the time correction unit performs the time synchronization operation by decoding the data header. Since it is started, SpaceWire can be used as it is without adding an extra hardware signal line.

  In addition, according to the communication device of the first embodiment, the synchronization data transmission unit transmits data indicating a code for starting and stopping the time synchronization operation other than the data format defined by SpaceWire, and time correction Since the unit decodes the data and performs the time synchronization operation, the data decoding unit of the user function at the subsequent stage can be omitted.

  Further, according to the communication apparatus of the first embodiment, the synchronous data transmission unit transmits the EOP transmission time by a plurality of times of time-code, and the time correction unit receives the bits received by the plurality of times of time-code. Since the time correction operation is performed with the above accuracy, even more accurate time synchronization can be realized.

Embodiment 2. FIG.
In the first embodiment, the initiator node 100 and the target node 200 are connected one-to-one by the SpaceWire 300, but the initiator node 100 and the target node 200 are connected via the SpaceWire router 500 as shown in FIG. This will be described below as a second embodiment. Note that the internal configurations of the initiator node 100 and the target node 200 are the same as those in the first embodiment, and a description thereof will be omitted here.

In the second embodiment, since one SpaceWire router 500 is sandwiched in the SpaceWire 300, the fluctuation of Time-Code transmission increases by one place.
When the internal clock of the oscillator 102a of the initiator node 100, the oscillator 205a of the target node 200 and the SpaceWire 300 is 50 MHz, and the link rate of the SpaceWire 300 is 2 MHz, the conventional method has been described in Embodiment 1 between the initiator node 100 and the SpaceWire router 500. Thus, a fluctuation of 5000 ns occurs. Further, since a fluctuation of 5000 ns occurs again between the SpaceWire router 500 and the target node 200, a total fluctuation of 10 μs occurs.

  On the other hand, in this embodiment, a 40 ns fluctuation occurs between the initiator node 100 and the SpaceWire router 500, and a 40 ns fluctuation occurs between the SpaceWire router 500 and the target node 200, resulting in a total fluctuation of 80 ns. As described above, even in the case of passing through the SpaceWire router 500, in this embodiment, it is possible to realize time synchronization accuracy with 125 times higher accuracy than the conventional method.

Embodiment 3 FIG.
In the second embodiment, the initiator node 100 and the target node 200 are connected via only one SpaceWire router 500. In contrast, in the third embodiment, as shown in FIG. 8, a plurality of target nodes 200-1 to 200- are connected via a SpaceWire network 301 including a plurality of cascade-connected SpaceWire routers 500-1 to 500-m. n is connected. In the third embodiment, the internal configurations of the initiator node 100 and the target nodes 200-1 to 200-n are the same as those in the first embodiment.

  In this case, the Time-Code is broadcast and transmitted to all the target nodes 200-1 to 200-n. By adding an address for a specific target node to the header part of the SpaceWire packet 400, the specific target node is transmitted. Only the SpaceWire packet 400 can be sent. In other words, in the conventional method, all target nodes are synchronized all at once, but in this embodiment, only a specific target node can be selected to perform the synchronization operation. As a result, the synchronization operation of the target node that requires time accuracy in particular can be performed, and an efficient operation can be realized.

  As described above, according to the communication device of the third embodiment, the SpaceWire router is provided between the initiator node and the target node, and a plurality of target nodes are provided. Therefore, the topology close to the actual use using the SpaceWire router. However, highly accurate time synchronization can be realized. In addition, time synchronization can be performed by selecting a target node that requires highly accurate synchronization.

Embodiment 4 FIG.
In the third embodiment, a tree-type network topology is configured using a plurality of SpaceWire routers. However, in the fourth embodiment, the SpaceWire routers 500-1 to 500-n are connected in a ring shape as shown in FIG. A SpaceWire network 302 is configured. Further, as illustrated, a plurality of target nodes 200-1 to 200-m may be connected. Each of the target nodes 200-1 to 200-m is the same as the target node 200 of the first embodiment.

  In such a topology, the initiator node 100 can have two SpaceWire interfaces. For this reason, even if one SpaceWire interface fails, time synchronization can be performed from the other SpaceWire interface.

  As described above, according to the communication device of the fourth embodiment, the SpaceWire router is composed of a plurality of SpaceWire routers configured in a ring type topology, so that one SpaceWire interface of the initiator node fails. However, synchronization can be performed using the other SpaceWire interface.

  In the present invention, within the scope of the invention, any combination of the embodiments, or any modification of any component in each embodiment, or omission of any component in each embodiment is possible. .

  DESCRIPTION OF SYMBOLS 100 Initiator node, 101 Data transmission part, 102 Time generation part, 102a Oscillator, 102b Time counter, 103 Synchronization start data transmission part, 103a Measurement counter part, 103b Start data transmission part, 104 Time-Code transmission part, 105 SpaceWire encoding part , 105a transmission FIFO, 105b serialization transmission unit, 200, 200-1 to 200-n target node, 201 SpaceWire decoding unit, 201a parallelization reception unit, 201b reception FIFO, 202 data decoding unit, 203 data reception unit, 204 reset 205, time generation unit, 205a oscillator, 205b measurement counter unit, 205c delay correction unit, 205d preset value, 205e time counter, 206 processing circuit unit, 300 SpaceWire, 301,302 SpaceWire network, 400 SpaceWire packet, 400a header, 400b data part, 400c termination part (EOP), 500, 500-1 to 500-n SpaceWire router.

Claims (9)

In a communication device composed of an initiator node and a target node connected by SpaceWire,
The initiator node encodes a SpaceWire packet and transmits it to the target node, and after stopping the NULL transmission of the SpaceWire encoder, the synchronization data and the transmission time of the synchronous data are sent to the SpaceWire encoder. A synchronous data transmission unit for transmitting,
The target node includes a transmission time of the synchronization data, a reception time of the synchronization data at its target node, and a difference between the transmission time and the reception time when the target node and the initiator node are in time synchronization. And a time correction unit that corrects the time of the target node. As the synchronization data, a SpaceWire packet including a header indicating the start of synchronization and an EOP (End of Packet) which is a terminal portion is used.
The synchronous data transmission unit notifies the transmission time of the EOP, and the time correction unit determines whether the notified transmission time of the EOP, reception time of the EOP, the target node, and the initiator node. The communication apparatus according to claim 1, wherein correction is performed using a difference between a transmission time and a reception time in a time synchronization state. The SpaceWire encoding unit includes a transmission FIFO, encodes a SpaceWire packet based on the data of the transmission FIFO,
3. The communication apparatus according to claim 1, wherein the synchronous data transmission unit stops NULL transmission by transmitting a data amount that makes the transmission FIFO full to the SpaceWire encoding unit. .   3. The communication apparatus according to claim 1, wherein the synchronization data transmission unit temporarily transitions to a time synchronization mode by a state transition of SpaceWire and stops NULL transmission of the SpaceWire encoding unit.   The synchronization data transmission unit transmits data with a header indicating a time synchronization operation, and the time correction unit starts a time synchronization operation by decoding the header of the data. The communication apparatus according to claim 4.   The synchronous data transmission unit transmits data indicating a code for starting and stopping a time synchronization operation other than the data format defined by SpaceWire, and the time correction unit decodes the data to perform time synchronization. The communication apparatus according to claim 1, wherein the communication apparatus performs an operation.   The synchronous data transmission unit transmits the transmission time of the EOP by a plurality of times of time-code, and the time correction unit performs a time correction operation with the accuracy of bits received by the plurality of times of time-codes. The communication device according to claim 2.   8. The communication apparatus according to claim 1, wherein a SpaceWire router is provided between the initiator node and the target node, and a plurality of the target nodes are provided. 9.   9. The communication apparatus according to claim 8, wherein the SpaceWire router includes a plurality of SpaceWire routers configured in a ring topology.

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