JPH06252928A - Real-time communications bus type lan - Google Patents

Abstract

PURPOSE:To provide a real-time communications bus type LAN which is useful to application of electronic musical instruments and can secure the reliability of real-time transmission without deteriorating the transmission efficiency by applying the different transmission systems in response to the priority of data. CONSTITUTION:A real-time communications bus type LAN is provided with an actuator station 1, the electronic musical instrument stations A 2 and B 3, a sound source station 4, a sequencer station 5, a synchronizer station 6, a means which detects the priority of data to be transmitted by plural transmission devices of a VTR station 7, a means confirms non-use of a bus 8 when the detected priority of data is higher than a prescribed level and immediately transmit the data in preamble length accordant with the priority, and a means which transmits the data after confirmation of non-use of the bus 8 and after a wait time secured according to the priority if the detected priority is lower than the prescribed level. The musical performance data are transmitted in higher priority, and the background data and the bulk data are transmitted in lower priority respectively. Then the synchronizing clocks requiring high accuracy are transmitted as the data of higher priority with which stricter priority control is possible.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bus type LAN for real time communication suitable for real time applications such as communication between electronic musical instruments.

[0002]

2. Description of the Related Art A basic technique widely known as a contention-type bus LAN is CSMA (Carrier).
There is a Sense Multiple Access) method. this is,
This is a method in which each node performs carrier sense and confirms that the bus is unused, and then starts transmission. There are the following three methods of waiting for access during carrier sense. -1-persistent Wait for the bus to become available, and then send it immediately. E
thernet uses this method. -P-persistent Wait for the bus to become free, wait a random time p after the bus becomes free, and then start transmission. It is said that the throughput will be about 80% by selecting the optimized p. -Non-persistent If the bus is in use without waiting for the bus to become vacant, consider it as an immediate collision and back off.

In the CSMA method, the immediate response ACK method is one in which the packet receiving side immediately returns a response signal ACK to detect the correctness of the transmission. CS
The method of improving throughput by adopting a collision detection mechanism on the transmission side of the MA method is CSMA / CD (CSM
A with Collision Detection). If there is a collision, the transmitting node immediately stops transmission, issues a jam pattern, and notifies the other nodes of the collision. It is said that this allows a throughput of 90% or more.

When constructing a LAN for electronic musical instruments, it is necessary that a plurality of types of data having different properties can coexist.
Possible data in this case include the following. (1) Clock for synchronization There are two clocks, a MIDI clock and SMPTE indicating absolute time. For example, the tempo is 1/480 notes (tempo 120 is about 4 ms), and SMPTE is 1/4 frame (30 frames / s is about 8.3 ms). The demand for delay is the strictest, but it is extremely sparse because it occurs at regular intervals,
It has a low load. Further, a MIDI clock or the like does not require a long data length, but real-time property is required. (2) Performance data It occurs asynchronously. In addition to actual performance data, there is also real-time control data for devices such as mixers. Although it is relatively sparse as a whole, in the case of a sequencer or the like, the load is locally high. (3) Background data Low-priority data that occurs asynchronously such as maintenance information and setup information. MIDI (Musical Instrumen
t Digital Interface) active sense, information for displaying the state of the device on the monitor screen, other information about human I / F, background inquiry / response, and the like. These pieces of information are not required to be real-time. (4) Bulk data Large-scale data such as sample data. It is transmitted according to the user's instructions and is not normally transmitted during performance.

Considering these various data, it is essential to introduce priority control. The following are typical methods that introduce priority control into the CSMA method. -Priority Ethernet This is a method in which the preamble length is changed according to the priority. Use long preambles for high priority data to survive the collision. However, collision detection is not performed for the preamble portion. Although the transmission efficiency of the high-priority data decreases, the priority control is reliable unless the packets of the high-priority data collide with each other.・ PW-CSMA / CD (CSMA / CD with Pri
orized Access Waiting) In Acknowledging Ethernet, this is a method of delaying the start of transmission for a certain period of time (that is, giving a certain access wait time) after confirming that there is no carrier by carrier sensing. Unlike Priority Ethernet, there is no reduction in the transmission efficiency of high priority data, but basically only low priority data is made difficult to flow,
Reliable priority control is not possible.

Considering the handling of various kinds of data as described above, the following design criteria are required when considering the system of the electronic musical instrument LAN. (A) Real-time transmission capability Optimized for synchronization clock / performance data transmission. For this purpose, the transmission efficiency of bulk data or the like may be somewhat lowered. (B) Small transmission delay In order to optimize the synchronization clock / performance data transmission, it is necessary not to reduce the average delay but to prevent a large delay from occurring. In other words, even if the efficiency under a low load is sacrificed to some extent, it is necessary that the maximum delay under a high load be as small as possible, specifically, the transmission delay in a music environment should be within 5 ms at the maximum. Assuming that the maximum number of MIDI events per clock is about 17, for example, in order to satisfy the maximum transmission delay of 5 ms, the target transmission time per event is about 200 μs (event transmission rate of 5 times or more of MIDI). . (C) There should be no error in the real-time performance data. The synchronization clock can be corrected based on past data even if there is a transmission error, but the performance data cannot be corrected. (D) Being a relatively small-scale network The number of connected units is small, usually about 10 and at most 30.
It is thought to be about the level In addition, it seems that at some point, at most 10 nodes will be able to simultaneously transmit packets.

In particular, reliability of real-time transmission is important. Not only in the contention system, in all LANs,
The software handshake is performed at any of the layers, and it relies on the software to finally obtain 100% reliability. However, in real-time transmission in electronic musical instrument applications, it is expected that one-to-many multicast communication such as MIDI will be frequently used, and the receiving station for the data output by the own station cannot be accurately grasped. I can't rely on software handshaking because I can't satisfy the delay,
You cannot get 100% reliability. Therefore, the transmission side retransmits only when the transmission side hardware detects a transmission error, and the reliability of the transmission is determined by the hardware. Therefore, a CSMA / CD system having a collision detection function is essential.

[0008]

As described above, considering the construction of the electronic musical instrument LAN using the existing system, the PW-CSMA / CD system does not reduce the transmission efficiency of high-priority data. However, the certainty of the priority control is insufficient, and the priority control is reliable in the Priority Ethernet method, but there is a problem that the transmission efficiency of the high priority data decreases because a long preamble is used for the high priority data. is there. The present invention has been made in view of the above points, and by adopting different transmission methods depending on the priority of data, the reliability of real-time transmission is ensured without reducing the transmission efficiency. It is intended to provide a LAN for real-time communication useful as

[0009]

SUMMARY OF THE INVENTION The present invention is a bus type LAN for real-time communication, which is connected to a bus shared by a plurality of transmission devices and performs carrier sense to confirm that the bus is unused before transmitting. The plurality of transmission devices, means for detecting the priority of the data to be transmitted, and if the priority is a predetermined value or more, after confirming the unused of the bus,
A means for transmitting data immediately and with a preamble length according to the priority, and when the priority is less than a predetermined value, after confirming that the bus is unused, a waiting time was taken according to the priority. And a means for transmitting data later.

[0010]

According to the present invention, the transmission device for handling a plurality of types of data belonging to low priority is a p-persistent type PW-C.
A transmission device that performs transmission control according to the SMA / CD system and handles a plurality of types of data belonging to high priority performs transmission control according to the 1-persistent type priority Ethernet system.
For example, in the electronic musical instrument application, there are many performance data,
Often concentrated at one time. On the other hand, background data such as maintenance information and bulk data such as tone color data are large, but transmission delay is not a problem. Therefore, in order to prioritize transmission of a large amount of real-time data such as performance data over background data and bulk data, performance data is transmitted as high-priority data in the p-persistent type PW-CSMA / CD system. However, for background data and bulk data, p-pe
It is transmitted as low priority data in the rsistent type PW-CSMA / CD system. The synchronization clock, which requires high precision but does not have a large amount of data, uses 1-persistent as high-priority data that enables more strict priority control.
Type priority Ethernet system. Thus, by changing the transmission control method according to the priority of the data to be transmitted, it is possible to perform highly reliable data transmission suitable for real-time use.

[0011]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a system configuration according to an embodiment of the present invention. As shown in the figure, the operator slave station 1, the electronic musical instrument station A2, the electronic musical instrument station B3, the tone generator station 4, the sequencer station 5,
A synchronizer station 6, a VTR station 7, etc. are connected to a bus (coaxial cable) 8. For connection, a transceiver (not shown) is attached to the bus 8 and each station is connected thereto by a cable.

The operation slave station 1 is provided with a keyboard and the like, and sends out real-time performance data in accordance with the performance of the performer. The electronic musical instrument station A2 is provided with a keyboard for playing, a musical tone synthesizing circuit for synthesizing musical tones, an operation panel for setting tone color information, etc., a sequencer for recording and reproducing sequence information, etc., and real-time performance data, MIDI clock, background data , Send bulk data, etc., and receive the same. It should be noted that the transmission / reception of the MIDI clock is performed by the electronic musical instrument station A.
It is alternatively selected by setting 2. Electronic musical instrument station B3
Has the same configuration as the electronic musical instrument station A2. However, it may not have a sequencer or the like.

The tone generator station 4 is provided with a tone synthesis circuit for synthesizing tones, sends background data, bulk data, etc., and receives real-time performance data, background data, bulk data, etc. The sequencer station 5 is provided with a sequencer for recording and reproducing sequence information such as performance, and sends out real-time performance data and MIDI clock and receives the same. Synchronizer station 6 is MI
In order to synchronize the VTR or the like with the DI device, the MIDI clock and SMPTE are transmitted and the SMPTE is received. In the above, the SMPTE, MIDI clock, and real-time performance data are real-time data, and the background data and bulk data are non-real-time data.

FIG. 2 is an internal block diagram of the electronic musical instrument station A2 in FIG. The lower part of the broken line shows the electronic musical instrument station A2. The data flowing on the bus 8 is the transceiver 8
1 and is provided to the communication interface 21. According to the control program stored in the ROM 23, the CPU 22 controls the keyboard section 25, the panel section 26, and the musical sound synthesis circuit 27 while using the RAM 24 as a temporary storage memory. When the performer operates the keys, the key switch 25a is turned on / off, and the keyboard interface 25b
Detects that state, it generates an interrupt signal to the CPU 22. Similarly, when the panel switch 26a is operated, an interrupt signal is generated by the panel interface 26b. When accepting each interrupt signal, the CPU 22 changes the state of the electronic musical instrument or instructs the musical tone synthesis circuit 27 to start / end musical tone generation based on the information that follows.

In addition to the above, the CPU 22 operates as a sequencer based on the program stored in the ROM 23. At the time of recording the sequence data, the real-time performance of the keyboard 25, step driving from the panel 26, and real-time performance data from the communication interface 21 are written in the RAM 24 as sequence data. At the time of reproducing the sequence data, the data stored in the RAM 24 is output to the tone synthesis circuit 27 or the communication interface 21 as real-time performance data. When the electronic musical instrument station A2 is set to transmit the MIDI clock, the MID is transmitted through the communication interface 21 at every time measured by the CPU 22.
When the I clock is set to be transmitted and the MIDI clock is set to be received, the tempo of the sequencer in the electronic musical instrument is controlled based on the MIDI clock received through the communication interface 21.

The tone synthesis circuit 27 forms a tone signal in response to an instruction from the CPU 22, and outputs a tone from the speaker 29 through the sound system 28. When the transceiver 81 receives a signal, the communication interface 21 performs electrical demodulation, decodes the packet to check the data destination, and checks the transmission error if the data is addressed to the own station or broadcast data. , Passes the data to the CPU 22. If the data is not addressed to itself, the data is ignored. When sending data from the CPU 22, as will be described later, a packet is generated by a method according to the priority of the data, the packet is electrically modulated, and the transceiver 8
Output to 1.

FIG. 3 is an internal block diagram of the sequencer station 5 in FIG. The sequencer station 5 is shown below the broken line. The data flowing on the bus 8 is taken out by the transceiver 82 and given to the communication interface 51. The CPU 52 controls the sequencer operation according to the operation of the panel unit 55 while using the RAM 54 as a temporary storage memory and a sequence data memory according to the sequencer control program stored in the ROM 53. When the panel switch 55a is operated, an interrupt signal is generated by the panel interface 55b. CPU5
When the interrupt signal is accepted, 2 changes the operation state of the sequencer based on the information that follows it.

When the sequencer station 5 is set to transmit the MIDI clock, the MI through the communication interface 51 is measured every time measured by the CPU 52.
When it is set to transmit the DI clock and receive the MIDI clock, the tempo of the sequencer is controlled based on the MIDI clock received through the communication interface 51. When the transceiver 82 receives the signal, the communication interface 51 performs electrical demodulation, decodes the packet to check the data destination, and checks the transmission error if the data is addressed to itself or is broadcast data. , Passes the data to the CPU 52. If the data is not addressed to itself, the data is ignored. When data is sent from the CPU 52, a packet is generated by a method according to the priority order of the data as will be described later, the packet is electrically modulated, and the data is output to the transceiver 82.

FIG. 4 shows the communication interface 21 of FIG.
It is a functional block diagram of. This circuit has a common configuration for all stations. The packet received by the transceiver is sent by the transceiver as a received signal,
It is electrically demodulated by the receiver 211 and given to the interface circuit 212. The interface circuit 212 takes out the data from the packet by the procedure described later and outputs the taken out data to the bus. A collision signal is supplied from the transceiver in addition to the received signal. The collision signal is given to the interface circuit 212, and collision detection of the signal is performed. Further, the collision signal is logically ORed with the received signal in the OR circuit 213 and is given to the interface circuit 212 as a carrier signal indicating that data exists on the bus.

The data provided to the interface circuit 212 via the data bus 8 is assembled here as a packet and is transmitted as transmitter data to the transmitter 214.
Is converted into an electric signal and output to the transceiver as a transmission signal. At the time of data transfer, a carrier signal and a collision signal are detected to control the operation. The specific operation of the interface circuit 212 will be described later.

FIG. 5 shows a data frame structure used in this embodiment. The preamble PA is, for example, 8
The bytes and the frame FR are, for example, 64 bytes. Pri
In stations that do not use the ority Ethernet system, both the preamble length and the frame length are fixed. DA / SA is a destination / source address, and Length indicates the length of the data Data. CRC is a cyclic redundancy code for error checking.

FIG. 6 shows the state of propagation delay in CSMA / CD. The propagation delay is composed of a rising delay (erased bit) and a steady delay, as shown in the figure. The signal for the rise delay time is received by the receiving circuit. It may not appear in the collision detection circuit. A time slot will be defined from the round trip propagation time until the signal is propagated to the farthest station, where a collision is detected and the jam signal is returned.

FIG. 7 shows how packets are transmitted from each station in this embodiment. Here, the priority is set to four levels. Priority 0 has the lowest priority, and background data and bulk data correspond to this. The second highest priority is priority 1, which is performance data transmitted from the operator slave station 1, the electronic musical instrument station A2, the sequencer station 5, and the like. These priority 0 and 1 packets are
It is transmitted by the PW-CSMA / CD system of a small fixed length frame. The performance data of priority 1 is transferred after waiting for a time determined by a random number value by the p-persistent algorithm from the time when the carrier signal is no longer detected on the bus. The packet corresponding to the background data or the like having the priority of 0 is further waited for a fixed access time, and then the transfer is started by the same waiting time as that of the p-persistent having the priority of 1.

For packet transmission of these priorities 0 and 1,
Collision detection is performed at the same time as carrier detection, and a linear backoff algorithm is used for backoff based on the result of collision detection. With the linear back-off method,
The initial window width is set to 10, for example, and the k-th time (k =
1, 2, ...) window width W (k) is W (k) = k
It is set to +9, and the backoff amount is a uniform random number within this range. Well-known backoff algorithms include binary exponential backoff, in which the window width doubles with each collision, but the transmission may be delayed significantly compared to the linear backoff. It is considered that this is because the initial window width of the backoff amount is small with respect to the number of nodes to be transmitted at the same time, so that many collisions occur and it becomes difficult to perform retransmission.

As shown in FIG. 7, the 1-persistent type Priority Ethernet system is adopted for the transmission of the synchronizing clock, and a higher priority is given to the real-time performance data. This is because the data amount is not so large as compared with the real-time performance data, but the accuracy of the transmission timing is required. Synchronous clocks in practical music environments often require only absolute time / relative time,
If there are at most two levels, it is possible to give them independent priorities. Here, MID indicating relative time
The I clock has priority 2 and SMPTE indicating absolute time.
Has the highest priority of 3. This allows
The synchronization clock can be transmitted without any collision. Since the synchronization clock has a small amount of information, there is no problem even if the sum of the preamble length and the frame length is fixed and the frame length is shortened by the increase in the preamble length, which prevents the transmission efficiency of high-priority data from decreasing. It

FIG. 8 shows the interface circuit 21 of FIG.
It is a flowchart which shows the operation | movement of the 2nd data transmission. This operation is common to the interface circuits of all stations. When data is received from the CPU in step 100, the process proceeds to step 102, and the priority order according to the received transmission data is set in the register. Here, SMPTE data has priority 3, MIDI clock has priority 2, MIDI clock has priority 2, real-time performance data has priority 1, and background data has priority 0. Assigned.

In step 104, it is judged whether or not the priority is higher than 1, and if it is high, the waiting time is set to 0 in step 106, and if it is low, p-pers is set in step 108.
The waiting time determined by a random number is set according to the istent algorithm. That is, the synchronization clock is set to the wait time 0, and the other data is set to the wait time according to the priority. In steps 110 to 118, carrier detection, waiting time counter reset when a carrier is not detected, judgment of elapse of a predetermined waiting time after the carrier is no longer detected, and the like are performed.

In step 120, the priority ether
Setting preamble length for net. With this, it is possible to control the preamble lengths of the priorities 3 and 2. Next, in steps 122 and 124, the PW-CSM is
A predetermined latency for the low priority level of A is realized.
In step 126, packet transmission is started. When collision detection is performed in step 128 by the end of transmission, collision processing including sending a jam pattern (step 132), calculating backoff time (step 134), and waiting for backoff time (step 136) is performed, and step 110 is performed.
Then, packet transmission is performed again. If the data transmission is normally completed, this is determined in step 130,
Return to step 110 to wait for the next data transfer.

As described above, in this embodiment, the background data, the bulk data and the performance data are transmitted by the PW-CSMA / CD system. Among them, the performance data is given a high priority and the linear backoff algorithm is used. By adopting, the real-time transmission of performance data is secured. Also, for synchronization clock transmission, P
By adopting the riority Ethernet method, strict priority control can be performed.

[0030]

As described above, according to the present invention,
By simultaneously using the PW-CSMA / CD method and the Priority Ethernet method in accordance with the priority of the data, a bus type LAN for real-time transmission useful as a LAN for electronic musical instruments can be obtained.

[Brief description of drawings]

FIG. 1 is a diagram showing a system configuration according to an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of an electronic musical instrument station of the same embodiment.

FIG. 3 is a diagram showing a configuration of a sequencer station of the embodiment.

FIG. 4 is a diagram showing a communication interface configuration of the embodiment.

FIG. 5 is a diagram showing a data frame structure of the embodiment.

FIG. 6 is a diagram showing how a data frame is delayed in the embodiment.

FIG. 7 is a diagram showing how data is transmitted in the embodiment.

FIG. 8 is a diagram showing a data transmission operation flow of the embodiment.

[Explanation of symbols]

1 ... Operator station, 2 ... Electronic musical instrument station A, 3 ... Electronic musical instrument station B,
4 ... Sound source station, 5 ... Sequencer station, 6 ... Synchronizer station, 7 ... VTR station, 8 ... Bus.

Claims (3)

[Claims] 1. A bus-type LAN for real-time communication, which is connected to a bus shared by a plurality of transmission devices and carries out carrier sense to confirm that the bus is unused before transmission. Means for detecting the priority of data to be transmitted, and means for transmitting data immediately and with a preamble length according to the priority after confirming that the bus is unused when the priority is equal to or higher than a predetermined value If the priority is less than a predetermined value, a means for transmitting data after confirming that the bus is unused, and after waiting according to the priority, real-time communication characterized by comprising: Bus type L
AN. 2. The real-time communication bus type LAN according to claim 1, wherein the transmission device keeps a total sum of the preamble length and the frame length constant. 3. The bus type LAN for real-time communication according to claim 1, wherein the transmission device linearly increases the backoff window width each time a collision is detected.