JP2000022743A - Asynchronous data communication method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable effective data transfer by transmitting necessary information without deficiency as reducing the number of packets by linking pieces of communication data and transmitting the contents of plural pieces of information as one packet. SOLUTION: One packet is formed by linking plural pieces of the communication data to be transmitted and two or more kinds of the communication data are transferred as one packet. For example, a command packet is outputted from a camera equivalent to the host side and acknowledgement(Ack) is replied by a printer to receive the command packet. Next, the data packet regarding information which is requested by a command accepted from the camera is transmitted by the printer and the acknowledgement is returned upon receiving the data packet by the camera. Such transmission of the data packet and return of the acknowledgement to it are repeated. A status is linked with parameter data related to the status and they are transmitted as one packet in this data communication method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an asynchronous data communication method on an interface bus linking a plurality of electronic devices, and more particularly to a data communication method suitable for asynchronous transfer of an IEEE 1394 bus.

[0002]

2. Description of the Related Art As an interface for connecting a plurality of electronic devices so that they can communicate with each other, for example, IEEE.
The E1394 bus is known. This IEEE 1394
The bus can be hot-plugged and up to 63 devices can be freely connected / node-branched in a daisy-chain (column) or tree-like manner regardless of master-slave.

As shown in FIG. 10, the IEEE 1394 bus has two transfer modes, an isochronous transfer mode (synchronous transfer mode) and an asynchronous transfer mode (asynchronous transfer mode). Up to 8 out of the nominal cycle period (= 125 μs)
0% can be allocated to isochronous transfer (Iso. Transfer) with the upper limit set to 0%, and the rest can be allocated to asynchronous transfer (Asynchronous transfer).
c. Transfer).

[0004] Isochronous transfer (Iso. Transfer) is performed prior to asynchronous transfer (Async. Transfer).
At every isochronous cycle that occurs every 25 μs, the isochronous channel that determines the maximum amount of data in advance and sends data within the secured amount of data to the secured isochronous channel is completed. After the completion of isochronous transfer, asynchronous asynchronous transfer is performed. .
You can also choose not to use Iso Transfer.
In this case, an entire cycle can be used for asynchronous Async. Transfer. The transfer rate of IEEE 1394 is 100 Mbps to 400 Mbps in the current standard, but further higher speeds are being studied in the future.

[0005]

However, the above I
In EEE1394, since each electronic device (node) connected to the bus can output an asynchronous transfer packet at least once every 125 μs, the data transfer efficiency deteriorates when the number of asynchronous packets having a small data amount increases. There is.

The above problem will be specifically described with reference to an example in which an electronic camera and a digital printer are connected using an IEEE 1394 bus as shown in FIG. The camera 10 corresponding to the host transfers various command information such as a print instruction, a parameter indicating detailed information of the command as necessary, and actual image data to be printed to the target printer 12. On the other hand, the printer 12 has a status (Stat) indicating whether or not the command content sent from the camera 10 can be fulfilled.
us) information and parameters indicating the state of the own device are returned to the camera 10 side.

FIG. 12 is a conceptual diagram showing a flow of communication exchanged between the camera and the printer, and FIG.
6 is a time chart corresponding to FIG. As shown in these figures, a command packet (“Comman
d ”. ) Is issued, and the printer 12 which has received the reply replies the recognition (indicated as “Ack.” In the figure). Recognition is coded and can represent completion (Good), hold, busy, error, etc. On the other hand, the printer 12 sends out a data packet corresponding to the received command, and the camera 10 receives this and returns an acknowledgment (Ack.). Sending out such a data packet and recognizing it (Ack.)
Is returned within one cycle (125 μs), and data transfer in packet units is repeated every cycle period. At this time, the printer 12 sends out the status information packet and the data packet such as the parameter related to the status as separate packets.

On the other hand, the camera 10 transmits the data and status sent from the printer 12 every 125 μs, as shown in FIG.
As shown in FIG. 5, the printer 12 stores the command and data sent from the camera 10 in the data register 14 and the status register 15 on the memory 13, respectively, in the command register 17 and the data register 18 of the memory 16. I do.

If it is assumed that the entire 125 μs is used for the Async transfer without using the Iso. Transfer on the IEEE 1394 bus, about one packet per 200 Mbps line is about 10 times.
00 bytes of data can be transferred. Although such a data amount can be transmitted in one packet, the data amount of status and command is actually about 1 to 256 bytes at most, and such a small packet is transferred every 125 μs. And the data transfer efficiency is degraded.

The present invention has been made in view of such circumstances, and in an asynchronous data communication in which data is transferred in units of buckets, necessary information is transmitted without a shortage while reducing the number of buckets, thereby improving efficiency. It is an object of the present invention to provide a data communication method that enables efficient data transfer.

[0011]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention provides an asynchronous data communication method for transferring data between electronic devices in units of packets by connecting a plurality of communication data to be transmitted. Thus, one packet is formed, and two or more types of communication data are transferred as one packet.

According to the present invention, the communication data is concatenated and a plurality of information contents are transmitted as one packet. Therefore, as compared with the conventional method in which each information content is individually transferred in one packet. , The number of packets can be reduced. Therefore, by applying the present invention to an interface in which a packet is transmitted every predetermined cycle period, data transfer efficiency can be further improved.

[0013] For example, as described in claim 2, a mode in which status information by communication and return data are linked, and these are transferred in one packet is conceivable. Also,
As described in claim 3, command information for giving an instruction to a receiving-side electronic device and parameter data related to the command information may be connected to form one packet. As in 3, the communication handshake information and the transmission data may be connected to form one packet.

In particular, when the asynchronous data communication method according to the present invention is applied to the IEEE 1394 interface, the data transfer efficiency of the asynchronous communication on the IEEE 1394 bus can be improved.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of an asynchronous data communication method according to the present invention will be described below in detail with reference to the accompanying drawings. First, the concept of the asynchronous data communication method according to the present invention will be described in comparison with a conventional method. In FIG.
An asynchronous data communication method according to the present invention
An example in which the present invention is applied to a bus is shown, and an example of data transfer between an electronic camera and a digital printer using an IEEE 1394 bus is schematically shown. FIG. 2 shows a time chart corresponding to FIG. FIGS. 1 and 2 respectively correspond to FIGS. 12 and 13 in the conventional communication method described above. As is apparent from a comparison between the two, as shown in FIG. The transfer mode is different from the conventional one.

As shown in FIGS. 1 and 2, a command packet is output from the camera 10 corresponding to the host, and the printer 12 receiving the command packet replies an acknowledgment (Ack.). Next, the printer 12 sends out a data packet related to the information requested by the command received from the camera 10, and the camera 10 receives this and returns an acknowledgment (Ack.). The transmission of such a data packet and the return of the acknowledgment (Ack.) To the data packet are repeated every 125 μs. The process up to this point is the same as the conventional method described with reference to FIGS.

However, in the data communication method according to the present embodiment, the status is linked to the parameter data related to the status (for example, information indicating what kind of error the status “error” is). However, this is different from the conventional method in which these are transmitted as one packet by dividing them into separate packets.

The data amount of the status is as small as about several bytes, and the status-related data is at most about 256 bytes. Even if both are connected, it is within the data amount (1000 bytes) allowed in one packet. Therefore,
By combining these two pieces of information and sending them simultaneously in one packet, the number of packets is reduced as compared with the conventional method (FIGS. 12 and 13).

As shown in FIG. 3, the camera 10 that receives a packet in which the status and its related data are linked has a status register 22 and a data register 24 on a memory 20. And the associated data are simultaneously stored in the status register 22 and the data register 24, respectively.

On the other hand, the printer 12 has a command register 32 and a data register 34 on the memory 30, and stores commands and data received from the camera 10 in the command register 32 and the data register 24, respectively. Although not shown in the figure, the command and
A mode in which the detailed parameters are concatenated and sent in one packet is also possible. In this case, a command to be received in one packet and its parameters are simultaneously stored in the command register 32 and the data register 34, respectively. Constitute.

Next, a more specific example will be described with reference to FIG. FIG. 4 shows a communication sequence when a SCSI command is sent between an electronic camera and a digital printer using the IEEE 1394 bus. After the bus reset is completed, first, the camera 10 issues a preparation confirmation request command to the printer 12 asking whether the printer 12 is ready. The printer 12 returns an acknowledgment (Ack.) In response to the received command. For example, if the user is ready, a response (Ack.) Indicating "Good" is returned.

Next, the next cycle period (= 125 μm)
In step s), the camera 10 issues a mode sense command to the printer 12 requesting that the current setting status of the printer 12 be read, and the printer 12 returns an acknowledgment (Ack.) to the command. The printer 12 that has received the mode sense command connects the status and mode sense information (corresponding to return data) in the next cycle period, and sends them as one packet. The mode sense information includes information such as the currently set number of pixels (set at the time of the previous use), the paper size, the starting position of the printing start, and the like.

After receiving such a packet, the camera 10 returns an acknowledgment (Ack.), And then rewrites only the necessary information in the mode sense information, and transmits the mode selection command and the mode selection data to 1 in the next cycle period. The packet is transmitted to the printer 12 side. The printer 12 returns an acknowledgment (Ack.) To this packet, and changes the settings such as the number of pixels and the paper size based on the mode select command received from the camera 10 and the selected data.

After the environment for both is prepared, a print command instructing execution of printing from the camera 10 and related parameters (for example, the number of prints and the number of data) accompanying the command are included in one packet. It is sent to the printer. The printer 12 receiving this packet returns an acknowledgment (Ack.). The printer 12 that has received the print command enters a print data reception standby state, and waits for reception of print data (image data) output from the camera 10.

The print data is divided into N blocks, and is sequentially sent to the printer for each block. The printer stores the print data in the memory 30 while returning the recognition (Ack.) For each received packet.
When the transfer of all print data is completed, the printer 1
2 executes print processing. Then, when the printing is completed, a status indicating the completion of the printing is issued. Upon receiving the print completion notification, the camera 10 returns recognition (Ack.).

The main difference between the above-described communication sequence and the conventional method will be pointed out again. First, regarding the response of the printer 12 to the mode sense command issued from the camera 10, the status and the mode sense information are linked. And sends it out as one packet.
Second, the camera 10 concatenates the mode select command and the related selection information and sends the packet to the printer 12 as one packet. And third,
The camera 10 concatenates the print command and the parameters related thereto and sends it as one packet to the printer.

As described above, the status and the parameters associated therewith, or the command and the parameters associated therewith, which are conventionally transmitted as separate packets, are transmitted together as one packet, so that the conventional method is used. , The number of packets can be reduced. Therefore, the IEEE has a rule that a packet can be output only at a constant cycle period (= 125 μs).
In the 1394 bus, transfer efficiency can be improved.

The combination of the command and the data may be a combination of a download command of a look-up table (LUT) and a corresponding parameter (data), in addition to the above. Further, in the above-described example, the case where two data items such as a status and a parameter or a command and a parameter are concatenated and transmitted as one packet has been described. The above items may be connected.

Next, a second embodiment of the present invention will be described. FIG. 5 shows a conceptual diagram of a data communication method according to the second embodiment of the present invention. Data to be transmitted (transmission data) is stored in the buffer 38 on the transmission side in a state where the data is divided every n bytes. When sending this transmission data according to a predetermined packet format, two types of packet formats are prepared.

The first format is, as indicated by reference numeral 41, a packet header 44, information (handshake information) 45 necessary for handshake, transmission data 46 for n bytes, and a CRC (cyclic redundancy data).
Check) It is composed of a transmission error control code such as a code 47. In this example, the handshake information means a flag indicating a first packet and a last packet when transmitting transmission data.

The second format includes a packet header 54, transmission data 56 for n bytes, a CRC code 57, and the like, as indicated by reference numeral 52.
Although a detailed communication sequence will be described later, when a plurality of transactions are required to send transmission data, the first packet and the last packet are transferred according to the first format, and the other packets are transferred according to the second format. (See FIG. 7).

On the other hand, a memory 60 on the receiving side is provided with a handshake register 62 and an n-byte data register 64, and the received handshake information and data are stored in these registers (62, 64). The data stored in the data register 64 is transferred to the buffer 68. Next, a data communication sequence of the IEEE 1394 interface configured as described above according to the embodiment of the present invention will be described.

FIG. 6 is a flowchart showing the flow of processing on the transmission side. When the transmission process is started, first, a pointer (pointer) is set to the head address of the transmission data in the buffer 38, and the handshake flag (HN
DSHK) is set to 1st pkt (a flag indicating the first packet) (step S110). Next, the value obtained by adding the packet division size n to the pointer and the buffer 3
8 is compared with the last address of the transmission data to determine the magnitude relationship (step S112). When it is determined that the pointer is smaller than the last address of the transmission data (No
(In the case of determination) means that all the transmission data in the buffer 38 cannot be transferred in one transaction, and the transmission data is transferred in a plurality of packets. In such a case, in the next step S114,
It is determined whether or not the handshake flag is set to 1st pkt, and it is determined whether the packet is the first packet or the second and subsequent packets (step S114).

When it is determined that the packet is the first packet (in the case of Yes determination), the packet is filled with the following information in accordance with the first format (reference numeral 41) described with reference to FIG. That is, the address of the handshake register 62 is described as the write address, and the n-byte transmission data from the handshake flag (HNDSHK) and the pointer (in this case, the transmission data start address) is described in the data area (step S116). .

Then, a write transaction of the set packet is issued (step S120). As a result, the first packet in the first format is transmitted. Thereafter, a value obtained by adding the packet division size n to the pointer is newly set as the pointer (step S12).
2), the process returns to step S112. Subsequently, a value obtained by adding the packet division size n to the pointer updated in step S122 is compared with the last address of the transmission data (step S112). At this time, if the pointer is smaller than the last address of the transmission data, the next step S
At 114, it is determined whether the handshake flag is set to 1st pkt. As described above, the handshake flag is set to HNDSHK = 1stpkt only at the time of forming the first packet (packet of the first format) in step S110.
After the first packet has already been transferred (second and subsequent packets) through step 16 and step S120, the handshake flag is not set to HNDSHK = 1st pkt. Therefore, when the step S114 is reached when transferring the second and subsequent packets, the determination here is No.

If it is determined in step S114 that the packet is the second or subsequent packet, the process proceeds to step S114.
Proceeding to 118, the packet is filled with the following information according to the second format (reference numeral 52) described in FIG.
That is, the address of the data register 64 is described as the write address, and n bytes of transmission data (the next n bytes of transmission data) are described from the pointer in the data area to form a packet (step S118). Then, a write transaction of this packet is issued (step S120). Thus, the packet in the second format is transmitted, and the process proceeds to step S122.
, And returns to step S112. While it is determined in step S112 that the pointer is smaller than the last address of the transmission data, steps S112 to S122 described above are performed.
Is repeated.

On the other hand, when it is determined in step S112 that the pointer is larger than the last address of the transmission data (in the case of Yes determination), it is next determined whether or not the handshake flag is set to 1st pkt. (Step S124). Only when this step S124 is reached when the first packet is transferred, the determination here is Y
If the answer is es and the process reaches the step S124 at the time of transferring the second and subsequent packets, the determination here is No.

If the determination is No in step S124, the handshake flag is set to HNDSHK = Lastpkt (step S126), and the packet is filled with the following information according to the first format. That is, the address of the handshake register 62 is described as the write address, and a packet describing n bytes of transmission data from the handshake flag (HNDSHK) and the pointer is formed in the data area (step S130).

Then, a write transaction of the set packet is issued (step S132). As a result, the last packet in the first format is transmitted, and the transmission processing is completed. On the other hand, if the determination is Yes in step S124, it means that the data transmission is completed in one transaction. In such a case, the handshake flag is set to HNDSHK = 1st pkt + Last p
kt (step S128) and step S130
Proceed to. Then, the address of the handshake register 62 is described as a write address in accordance with the first format, and a packet in which n bytes of transmission data (in this case, n bytes from the start address of the transmission data) is described in the data column is a pointer. Formed (step S130), the first
The packet is transferred in the format (step S1).
32).

FIGS. 7 and 8 show time charts of the above-mentioned transmission processing. FIG. 7 shows an example in which a plurality of transactions are required to transmit data, and FIG. 8 shows one transaction in transmitting data. This is an example of a case in which the process can be completed. As shown in these figures, when a plurality of transactions are required, a packet in which the handshake data and the transmission data are connected in the first format for the first packet and the last packet is formed, and this packet is formed into one packet. Transfer as Also, in the case where the data transmission is completed in one transaction, a packet in which the handshake data and the transmission data are connected is formed, and this is transferred as one packet.

FIG. 9 is a flowchart showing the flow of processing on the receiving side. The reception interrupt processing shown in FIG.
It is started by a transaction reception interrupt of the E1394 bus, and first, it is determined whether or not the writing is to the handshake register 62 (step S160). When writing to the handshake register 62 has been performed, it is determined whether or not a flag (1st pkt) indicating the first packet has been written to the handshake register 62 (step S162).

If it is determined that the packet is the first packet, the pointer is set to the start address of the buffer 68 (step S164), and the contents of the n bytes of data (data register) transmitted in connection with the handshake data are transmitted. The data temporarily stored in the buffer 64 is transferred to the address indicated by the pointer (in this case, the starting address of the buffer 68) (step S166).

Thereafter, it is confirmed whether or not a flag (Last pkt) indicating the last packet is written in the handshake register 62 (step S16).
8). When a one-transaction completion type packet as shown in FIG. 8 is transmitted from the transmission side, a flag (HNDSHK = 1st pkt +) indicating both the first packet and the last packet as handshake data
Last pkt) is included, and in such a case, the determination in step S168 becomes Yes, and the data reception is completed.

On the other hand, when the first packet of the multi-transaction type as shown in FIG. 7 is transmitted from the transmitting side, the determination in step S168 becomes No, and the process shifts to waiting for an interrupt. Next, when the reception interruption of the second and subsequent packets is started, it is determined again whether or not the handshake register 62 has been written in step S160. In the multi-transaction type transfer, in the case of the packet transfer in the second format, since there is no writing to the handshake register 62, in such a case, the determination in step S160 is No, and the process proceeds to step S1.
Go to 72. In step S172, the data register 6
4 is determined, and if no data is written to the data register 64, processing other than data reception is performed according to a predetermined agreement (step S174).

On the other hand, if there is a write to the data register 64 in step S172, the packet division size n is added to the currently set pointer (the start address of the buffer 68 in the case of the second packet), and The value is set as a new pointer (step S176), and the contents of the n-byte data temporarily stored in the data register 64 are transferred to the address indicated by the pointer (step S180). After that, it is in the interrupt waiting state.

During the period for transferring the packet in the second format shown in FIG.
The processing of 172 to S180 is repeated. Eventually, when processing of the last packet (packet in the first format) is performed, writing to the handshake register 62 is performed.
The determination is s, and the process proceeds to step S162. In the case of the last packet in the multi-transaction type, a flag (HNDSHK = Last pkt) indicating that the packet is the last packet is written in the handshake register 62, so that the determination in step S162 is No, and the process is terminated. The process moves to step S182.

That is, after confirming the flag indicating the last packet (step S182), a value obtained by adding the packet division size n to the currently set pointer is set as a new pointer (step S18).
4). Next, the contents of the n-byte data (data temporarily stored in the data register 64) transmitted in connection with the handshake data are transferred to the address indicated by the pointer (step S186), and the data reception is completed.

According to the present embodiment, the transmission data and the data for handshake are transmitted as one packet, so that the communication efficiency is improved as compared with the conventional method of transmitting these data as separate packets. Can be improved. In the above embodiment, the IEEE1394
Although the asynchronous communication system has been described as an example, the present invention can be applied to other types of asynchronous data communication.

[0049]

As described above, according to the asynchronous data communication method of the present invention, data to be transmitted is linked,
Since a plurality of information contents are sent as one packet, the number of packets can be reduced as compared with the conventional method in which one packet is transferred for each communication data.
Data transfer efficiency can be improved.

In particular, when the present invention is applied to the IEEE 1394 interface, the data transfer efficiency of asynchronous transfer on the IEEE 1394 bus can be improved.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing an example of data transfer in asynchronous transfer of an IEEE 1394 bus according to an embodiment of the present invention.

FIG. 2 is a time chart corresponding to the data transfer shown in FIG.

FIG. 3 is a conceptual diagram showing a memory map of the camera and the printer shown in FIG.

FIG. 4 is an explanatory diagram showing a communication sequence when a SCSI command is sent between an electronic camera and a digital printer using an IEEE 1394 bus.

FIG. 5 is a conceptual diagram for explaining a data communication method according to a second embodiment of the present invention.

FIG. 6 is a flowchart illustrating a flow of a transmission process according to the second embodiment of the present invention;

FIG. 7 is a time chart when a plurality of transactions are required to send data.

FIG. 8 is a time chart when data is sent in one transaction.

FIG. 9 is a flowchart illustrating a flow of a reception interrupt process according to the second embodiment of the present invention;

FIG. 10 is an explanatory diagram showing an IEEE 1394 bus data transfer method;

FIG. 11 shows an electronic camera and a digital printer connected to IEEE1.
Block diagram showing a system connected using a 394 bus

FIG. 12 is a conceptual diagram showing an example of data transfer in asynchronous transfer of a conventional IEEE1394 bus.

FIG. 13 is a time chart corresponding to the data transfer shown in FIG.

FIG. 14 is a conceptual diagram showing a memory map of a camera and a printer in a conventional system.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Camera 12 ... Printer 22 ... Status register 24 ... Data register 32 ... Command register 34, 64 ... Data register 45 ... Handshake information 46, 56 ... Transmission data 38, 68 ... Buffer 62 ... Handshake register

Claims (5)

[Claims] 1. An asynchronous data communication method for transferring data between electronic devices in units of packets, wherein a plurality of communication data to be transmitted are connected to form one packet, and two or more types of communication data are transmitted. An asynchronous data communication method, wherein the data is transferred as one packet. 2. The asynchronous data communication according to claim 1, wherein the status information and the return data by communication are connected to form one packet, and the status information and the return data are transferred in one packet. Method. 3. Command information for giving an instruction to a receiving device and parameter data related to the command information are connected to form one packet, and the command information and parameter data are transferred in one packet. 2. The asynchronous data communication method according to claim 1, wherein: 4. The asynchronous data communication according to claim 1, wherein the handshake information of the communication and the transmission data are connected to form one packet, and the handshake information and the transmission data are transferred in one packet. Method. 5. The method according to claim 1, wherein the method is applied to asynchronous transfer on an IEEE 1394 bus.
An asynchronous data communication method according to any one of the above.