JPH02125545A - Data reception control method in lan - Google Patents

Abstract

PURPOSE:To reduce the loss of an input data by sending a jamming signal when an input data from a LAN transmission line exists when there is no margin in a function receiving the data. CONSTITUTION:A reception enable signal 3 is inputted with branch informing the data input start from a transmission line to a LANC to a jamming signal generator 2, and the generator 2 outputs a jamming signal 4 in the presence of an input of the reception enable signal 3 when a buffer busy 1 is set to a busy state. The same state as data collision takes place in a LAN transmission line, the LANC aborts the data not received and the data transmission side interrupts the data transmission and the interrupted data is sent again after an optional waiting time. The data reception side uses the time till the retransmission is used for the processing of the data stored in a reception data buffer.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a data reception control method in a LAN, and particularly to a data reception control method in a LAN.
multiple access/collisi
The present invention relates to a data reception control method in a LAN (on detection) method.

[Conventional technology]

The C3MA/CD type LAN uses a logical bus-type transmission path and has a collision detection function when sending data simultaneously and a data retransmission processing function, and is compliant with IEEE802.
．． There are 3 standards and 1 standard. In this LAN, data consists of a destination address, a source address, and a CR.
It is transmitted and received using frames containing C codes and the like.

The data length in a frame is variable, with a minimum frame length of 64 octets and a maximum of 1518 octets,
When the bit rate of the transmission path is 10μbps, the minimum is 51.
The maximum time length is 1214.4 μsec.

Also, the time interval between frames (int, erf
ramegap) is a minimum of 9.6 μsec. A dedicated LSI has been developed and commercially available as a circuit for realizing such a LAN, and this is referred to as a LANC (local area network) hereafter.
area network control
r).

LANC is connected to the CPU bus of a microcomputer, etc., and based on operation instructions from the CPU, sends data from the transmission data buffer connected to the CPU bus to the LAN transmission path, and conversely, sends data from the LAN transmission path. It has a function that autonomously performs operations such as writing data to the reception data buffer, and when receiving data from the transmission path, it checks whether there is space in the reception data buffer by itself, and if there is no space, It is used to discard received data. This means that data processing on the receiving side of the LAN takes time and data sent while the receive data buffer is full will be lost on the LAN.

In addition, this kind of control method is allowed in parts that provide MAC sublayer functions, such as LANC, and generally, the communication procedure part located in a higher layer uses frame serial numbers or Deficiencies in the data transmission path are compensated for by using reception responses. Further, the communication procedure of the upper layer makes it possible to avoid the busy state of the LANC reception data buffer.

In addition, in the LAN, if data with the minimum frame length is sent at the minimum frame interval, one frame will be received every 60.8 μsec, and the LAN will notify the CPU of data reception every time this one frame is received. CPU
performs the processing associated with data reception.

Notification of data reception from the LANC to the CPU is performed by having the CPU execute interrupt processing;
In a typical microcomputer used as U, it takes several tens of μs just to move the process to interrupt processing and return.
sec, and additional time is required for the interrupt processing itself.

Therefore, when the minimum frames are sent at the minimum time interval, the CPU may not be able to process the data reception interrupt from the LANC.

[Problem to be solved by the invention]

The data reception control method in the conventional LAN described above is as follows:
Since LAN terminals follow a specified communication procedure, it is usually rare for the minimum frame to be continuously received at the minimum time interval, and in the unlikely event that the processing is not done in time, data loss may occur. Even if there is, it can be sufficiently compensated for by requesting retransmission due to communication procedures.

However, in the case of a bridge connection that connects LANs and enables communication across multiple LANs, multiple communication buses are concentrated, and the situation where the minimum frame must be continuously received is limited to the data buffer of a normal terminal. It has the disadvantage that data loss is more likely to occur in areas where it is more likely to be busy and where the smallest frames are sent in a concentrated manner.

[Means to solve the problem]

The data reception control method in a LAN according to the present invention is a method for controlling data reception in a LAN.
It has means for determining whether or not data input from the transmission path can be received, and means for sending out a jam signal that causes a collision with the data on the LAN transmission path when the data cannot be received.

〔Example〕

Next, the present invention will be explained with reference to the drawings. 1 and 2 are block diagrams of the first and second embodiments of the present invention, and FIGS. 3 and 4 are flowcharts for explaining the operations of the first and second embodiments.

In the first embodiment shown in FIGS. 1 and 3, buffer busy 1 is set to ``J'' when the CPU monitors whether the receive data buffer of the LANC is empty and there is no empty buffer. Cleared when exists.

The jam signal generator 2 receives a branch input of the reception enable signal 3 that informs the LANC of the start of data input from the transmission path, and generates a jam signal when the reception enable signal 3 is input when the buffer busy 1 is set to busy. Outputs 4.

The jam signal 4 is a 32-bit length PA1°"'o" inverted continuous signal, and by merging this signal with the data output signal line of the LANC and sending it out, the jam signal 4 is transmitted on the LAN transmission line.
The situation is the same as a data collision, and the LANC discards the data that was about to be received, and the data sending side interrupts data transmission and retransmits the interrupted data after an arbitrary waiting time.

On the data receiving side, this time until retransmission can be used to process the data stored in the received data buffer.

In this way, as shown in FIG.
Then, when there is no input data from the transmission line, there is no enable signal and standby (S2) L; when there is input data, the enable signal is input to the jam signal generator, and the process goes to step S.
When the buffer No. 3 is empty, the data is received by the LANC (S4), and when the buffer is busy (no empty space), a jam signal is sent onto the LAN transmission path (S5) to cause a collision with the input data.

In the second embodiment of FIGS. 2 and 4,
A branched LANC enable signal 13 is input to I. The enable signal 13 is a signal that notifies the LANC that there is data input from the transmission line.The logic level is ON during data input, and is OFF when no data is input.
It becomes F. Busy FFII indicates that the enable signal 13 is O.
When it changes from FF to ON and then returns to OFF, it becomes set state. When busy FFII is set, data is input from the transmission path, and enable signal 13 is OFF.
When F is turned ON, the jam signal generator 12 sends out a jam signal 14.

The jam signal 14 is similar to the jam signal 4 of the first embodiment, and by merging this jam signal 14 with the data output signal line of the LANC and sending it out, the same state as a data collision occurs on the transmission line. , the LANC discards the data it was about to receive, and the sender interrupts data transmission and retransmits the data after a random waiting period.

The CPU resets the busy FFII when it completes the interrupt processing due to the data reception interrupt from the LANC,
Enables reception of subsequent frames.

In this case, as shown in FIG. 4, the busy FF 13 is set (S2) at the time when the enable signal 13 is detected to change from OFF→○N→OFF. After that, if the enable signal 13 turns OFF to 0N (S3) until the busy FF 13 is reset by the CPU, the jam signal 14 is sent out (S4), causing a collision with the input data on the LAN transmission path. .

〔Effect of the invention〕

As explained above, in the present invention, when there is no margin in the data receiving function and there is input data from the LAN transmission line, a jam signal is sent out to cause a collision with the input data and the data is sent to the transmitting side. By interrupting the transmission of the data and retransmitting the data, there is an effect of reducing the loss of input data because the data reception interrupt time can be increased.

[Brief explanation of the drawing]

1 and 2 are block diagrams of the first and second embodiments of the present invention, and FIGS. 3 and 4 are flowcharts for explaining the operations of the first and second embodiments. 1... Buffer busy 2, 12... Jam signal generator, 3, 13... Enable signal, 4, 14...
Jam signal, 11...busy FF.

Claims (1)

[Claims] means for determining whether or not data input from a LAN transmission line can be received;
1. A data reception control method in a LAN, comprising means for sending a jam signal that causes a collision with data on a transmission path.