JP2003037596A - Communication device and communication method - Google Patents

Abstract

(57) [Problem] To provide a communication device and a communication method capable of setting a data payload size of a packet flowing on a bus to an appropriate size. An IEEE13 capable of transmitting and receiving data by isochronous transfer and asynchronous transfer.
94 device (101) that transmits and receives data to and from an external device connected via a communication interface
An EEE1394 interface control unit (103), a data payload size setting processing unit (108) for determining the responsiveness of a communication destination external device when transmitting / receiving data by asynchronous transfer; Can change the data payload size at the time of transmission / reception in asynchronous transfer according to the responsiveness of the external device of the communication destination.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a communication device and a communication method having a serial bus interface, and more particularly to a communication device and a communication method having an interface compliant with the IEEE 1394 standard, and to setting of a data payload size of a packet. Is.

[0002]

2. Description of the Related Art In recent years, serial bus interfaces are
Fewer signal lines, thinner cables, smaller connectors, no need to set ID, terminator, etc., hot-swap capability, and isochronous data transfer (isochronous transfer) It has been in the limelight because of its excellent features such as.

In particular, the serial bus interface defined by IEEE 1394 is capable of high-speed transmission of a large amount of data such as moving images, is capable of memory access depending on the bus architecture, and is capable of hot plug-in and plug-and-play. And that it has peer-to-peer connectivity,
Not only personal computers but also home AV devices (digital video cameras, etc.) and other devices are being actively applied. Also, a new standard (for example, P1394.b) that supports further speedup and longer distances
Is currently under active development.

In IEEE 1394, isochronous transfer, which is a data transfer mode in which a certain band is guaranteed in a cyclically continuous time zone, and a retransmission procedure is not performed even when an error occurs, and an error is generated without guaranteeing the band. In case of occurrence, two kinds of transfer modes called asynchronous transfer, which is a transfer mode that guarantees reliable data transfer by a retransmission procedure, are provided. Isochronous transfer is mainly used for moving image data that is required for large-capacity and real-time characteristics found in digital video cameras, and asynchronous transfer is mainly used for transferring to devices such as storage devices, printers and scanners where data loss is not allowed. To be done. Since isochronous transfer has a higher priority as a transfer mode, asynchronous transfer uses a surplus band that is not used in isochronous transfer. Also, in the asynchronous transfer, a retry protocol is provided that enables the packet to be retransmitted when the receiving node cannot receive the packet (busy state).

[0005]

However, in the above-mentioned conventional technique, when a large number of devices are connected to the IEEE 1394 standard bus and each of them performs data transfer, the traffic increases to maintain the intended transfer rate. Becomes difficult. In particular, a relatively large amount of data is exchanged for frequent reading and writing to a large-capacity storage device such as an HDD or MO and for data transfer with a printer or a scanner. In addition, CCD on the bus
If a device such as a camera or a DVC is connected, a band used for isochronous transfer is secured, so that the band for asynchronous transfer per cycle is limited.
Therefore, it becomes more difficult to complete the transfer of the large amount of data within a desired time. For example, 2 in 1 cycle
If the asynchronous transfer with 048 bytes of data payload is restricted so that it can be performed only once (on the contrary, the IEEE 1394 standard guarantees a band with which at least asynchronous transfer with the above data payload size can be performed. ), The same band will be used alternately by multiple devices. If four devices that want to send a large amount of data by asynchronous transfer are connected to the bus, there will be an opportunity to send only once in four cycles, and considering the bandwidth for sending response packets. The cycle that goes around becomes longer.

Further, depending on the data processing unit, the processing capacity, and the system configuration of the node that receives the request packet, the maximum data payload size that can be received (or can be transmitted in the case of a read transaction) is the data. When transfer is performed, there is a situation in which the packet cannot be received at the timing when the transmitting node sends it, that is, the receiving node becomes busy. In that case, frequent retries occur and transfer efficiency cannot be improved.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a communication device and a communication method capable of setting the data payload size of a packet sent on a bus to an appropriate size. To aim.

[0008]

In order to achieve the above object, the communication device of the present invention is capable of transmitting and receiving data by isochronous transfer and asynchronous transfer, and is connected via a communication interface. Communication means for transmitting / receiving data to / from an external device, and determining means for determining the responsiveness of the external device of the communication destination when transmitting / receiving data by asynchronous transfer, and the asynchronous transfer according to the determination by the determining means. And a changing means capable of changing the data payload size at the time of transmission / reception.

Further, the communication method of the present invention is a communication means capable of transmitting / receiving data by isochronous transfer and asynchronous transfer, and transmitting / receiving data to / from an external device connected via a communication interface. In the communication method, when data is transmitted / received by asynchronous transfer, a judgment step of judging the responsiveness of the external device of the communication destination, and a data payload at the time of transmission / reception in the asynchronous transfer according to the judgment by the judgment step. And a changing step capable of changing the size.

According to the above configuration, the data payload size of the packet sent on the bus can be set to the optimum data payload size for the communication partner device. As a result, it is possible to shorten the transfer time when transferring a large amount of data, and reduce the number of transmissions and retries, which enables effective use of the bus and improves overall system performance. Become.

According to a preferred aspect of the present invention, the communication device obtains information on a transfer band used in asynchronous transfer on a bus to which the communication device is connected via the communication interface. The method further includes an acquisition unit and a setting unit that sets the data payload size based on the information about the transfer band acquired by the acquisition unit, and the operations of the acquisition unit and the setting unit are the determination unit and the change. It is performed before the action by means.

In the communication method, an acquisition step of acquiring information on a transfer band available for asynchronous transfer on a bus connected to the communication device via the communication interface, and an acquisition step in the acquisition step And a setting step of setting the data payload size based on the information about the transfer band, wherein the obtaining step and the setting step are performed prior to the determining step and the changing step.

According to a preferred aspect of the present invention, in the acquisition means and the acquisition step, the transfer ROM is read by reading a configuration ROM and a control and status register of each external device connected to the bus. Get information about bandwidth.

Further, according to a preferred aspect of the present invention, the information regarding the transfer band includes the number of external devices that perform isochronous transfer, and the isochronous transfer bandwidth and the number of channels acquired by the external device.

Further, the information regarding the transfer band includes the number of external devices connected to the bus.

Further, according to a preferred aspect of the present invention, the self-ID packet transmitted from each external device connected to the bus after the reset of the bus is obtained in the obtaining means and the obtaining step. The information regarding the transfer band is acquired by.

Further, according to a preferred aspect of the present invention, in the setting means and the setting step, when the information regarding the transfer band satisfies a predetermined condition, the maximum transferable data payload size is set. To do.

Preferably, the predetermined condition is that the band left for asynchronous transfer is larger than the predetermined band.

More preferably, the predetermined condition is that the number of external devices, other than the communication device, connected to the bus that performs asynchronous transfer is smaller than a predetermined number.

Further, according to a preferred aspect of the present invention, in the judging means and the judging step, the minimum time required to complete the transaction performed by the communication device and the external device of the communication destination are set. Compare with the response time.

According to a preferred aspect of the present invention, the time required for the external device of the communication destination to respond is the response packet after the communication device transmits a request packet to the external device of the communication destination. This is the time it takes to receive.

According to a preferred aspect of the present invention, the communication device further includes a timer for measuring a time required for a response by the external device of the communication destination, and the communication method is an external device of the communication destination. The apparatus further includes a timing step of measuring the time required for the device to respond.

Further, according to a preferred aspect of the present invention, in the changing means and the changing step, the data payload size value is reduced when the response of the external device of the communication destination is low.

Preferably, the communication means is IEEE1
It conforms to the 394 standard.

[0025]

Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 is a block diagram showing an outline of the system in this embodiment.

Reference numeral 101 denotes an IEEE 1394 device which is a node on the side of transmitting a request packet corresponding to the IEEE 1394 interface. Here, it is assumed that the device has a printer function. As shown in FIG. 1, each I from 103 to 108 described below
EEE1394 layer, timer 109, printer function 1
10 and a CPU (not shown), a reception buffer, and the like.

Reference numeral 102 denotes an IEEE 1394 interface bus. The nodes on this bus are connected by cables. Two twisted pair cables (one is called A and the other is called B) in the cable
And a pair of power pair cables, a total of 6 cables are crossed. In addition, there are some that are composed of four cables without a power line.

Reference numeral 103 is an L for realizing a function of directly driving a signal on an IEEE 1394 interface called a PHY layer or a physical layer (physical layer).
An IEEE 1394 interface control unit configured by SI and an LSI that realizes the functions of the LINK layer (link layer). It performs processing such as transmission of request packets, reception processing of response packets including print data sent from the node that receives the request packets, and bus configuration.

A driver 104 manages and executes an actual operation for an IEEE 1394 interface called a transaction layer, and also includes a function of a part of the link layer. In this layer, IEEE13
Manages read / write / lock transactions for asynchronous transfer performed on the 94 interface.
Control. A retransmission (retry) request when the receiving node is busy is also managed in this layer. Also, the timer 109 is started and stopped for measuring the time from the transmission of a request packet to the reception of a response packet, which will be described later.

Reference numeral 105 denotes a layer for performing serial bus management (SBM), which is a node controller constituted by an IEEE 1394 interface management driver. As a function, it mounts a CSR (control and status register) and a configuration ROM and manages other node information. In particular,
The presence / absence of a node that performs isochronous transfer is confirmed, and if there is, the operation for acquiring the secured bandwidth and number of channels for isochronous transfer from the register of the isochronous resource manager node on the bus is performed. It also handles management of other node information that accompanies reception of self-ID packets. SBM is a node controller 1
It is possible to have functions of an isochronous resource manager and a bus manager as functions other than 05, but since it is an option, the IEEE 1394 device 1
01 does not have to have the function.

The configuration ROM is ISO /
Stores various types of information held by nodes defined by IEC13213, and is in a minimal format (Minimal F
There are two types of formats: ormat) and general format. The minimal format has only node_vendor_id information that identifies the manufacturer. General format is Bus_info_Block
And with additional information called Root_Directory. IEEE
The 1394 device 101 has a general format.

Reference numeral 106 is an application layer of IEEE1394. It is configured by an application 107 for realizing the printer function described below and a data payload size setting processing unit 108 (described later) that sets a data payload size value that is a feature of the present embodiment.

Reference numeral 107 is application software having software for realizing functions of various devices using the IEEE 1394 interface, for example, functions of a printer, a scanner, a digital video camera, etc., and an interface with a transaction layer and a node controller. Since a printer device is assumed in the present embodiment, command analysis of print data, image processing (correction processing and decompression processing of compressed data), and control of the recording unit of the printer are also performed. In addition, SBP-
It also has the functions of higher-level protocols suitable for IEEE 1394 such as 2 and DDP. In the print data transfer by the SBP-2 protocol, the printer side takes the initiative and transmits the read request packet. In the present embodiment, a PC is assumed as the receiving node, and a response packet having print data as a data payload is transmitted in response to a request from the printer device.

Reference numeral 108 denotes a data payload size setting processing unit which sets the data payload size at the time of transmitting the request packet by judging from various information. The data payload size setting processing unit 108 has the following functions. That is,

1. From the node controller 105, information such as the number of nodes forming the bus, the bandwidth secured for isochronous transfer, and the number of channels is acquired.

2. The IEEE 1394 driver 104 is instructed to measure the time taken from the transmission of the request packet to the reception of the response packet, and the obtained time is grasped. Also, the frequency of retries that occur due to the busy state of the receiving node when transmitting the request packet is understood.

3. It has, as a reference value, a value that is acceptable as the time required from the transmission of a request packet to the reception of a response packet. In addition, the above 1 and 2
The optimum data payload size is obtained and set from the information obtained in step 1 and this reference value. The method of determination and setting will be described later with reference to the flowcharts shown in FIGS. 3 and 4.

Reference numeral 109 denotes an IEEE 1394 driver 10
4 is a timer managed by 4. It is started when a request packet is sent and stopped when a corresponding response packet is received, and the time between them is measured. In this embodiment, a dedicated hardware timer for time measurement is assumed, but a split timer provided in the link layer of the IEEE 1394 I / F control unit 103 (a timer for detecting timeout of split transaction)
Alternatively, it can be realized by using a timer provided in a CPU (not shown).

Reference numeral 110 denotes a printer function controlled by software of the application 107 or hardware (not shown). Print the received print data. It also has a function of returning the status on the printer side to the application 107.

Next, an outline of the data payload size setting process will be described.

First, at the time of bus reset caused by connection or disconnection of a new device to the bus and power-on, information on the nodes constituting the bus is acquired. Specifically, the node controller 105 stores the self-ID packet of each node to grasp the number of nodes, and further, when there is a node performing isochronous transfer, the bandwidth and the number of channels secured for isochronous transfer. Confirm operation of. The acquired information is used by the data payload size setting processing unit 108.

After that, when receiving a large amount of data such as print data, the initial value of the payload size at the time of data transfer is set based on the information grasped at the time of the bus reset.

After the data transfer is started, the time from the transmission of the request packet to the reception of the response packet is confirmed for each transaction, and if the transaction is not completed within the allowable time or if frequent retries occur, the data is transferred. Set the payload size value smaller than the initially set value.

In this embodiment, the request packet transmitting node (IEEE1394 device 101)
Although the above is used as a printer device, a PC, a digital still camera, a scanner device, or the like that serves as a host that transmits data to the printer by a write transaction may be assumed.

FIG. 2 is a flow chart of information acquisition processing performed at the time of bus reset in this embodiment.
Normally, in IEEE 1394, a read transaction for acquiring information of each device connected to the bus is performed a plurality of times at the time of bus reset, and therefore necessary information is acquired in accordance with the read transaction.

In step S201, the number of self-ID packets is counted. When the bus is reset, all devices connected to the bus broadcast the self-ID packet. IEEE of the present embodiment
The 1394 device 101 receives and stores these self-ID packets, and determines the number of IEEE 13 packets on the bus.
Figure out if 94 devices are connected. Also, the node in which the C bit (CONTENDER bit) in the self ID packet is set is grasped. This is to identify the node that has become the isochronous resource manager. ID among the nodes with the C bit set
The node with the largest is the node that supports the isochronous resource manager.

In step S202, a read transaction for obtaining the information in the configuration ROM of each device connected to the bus is issued. Specifically, Bus_Info_B in the configuration ROM
By checking the isc bit in lock, it is determined whether or not the device is capable of isochronous transfer. Also, by acquiring the information in the Node_Unique_ID leaf,
Understand the type of device and its function.

In step S203, step S202
Check the configuration ROM information obtained in
It is determined whether or not any node supports isochronous transfer. When the information acquisition result node exists, the process proceeds to step S204, and when it does not exist, the process ends.

In step S204, in order to confirm whether or not the node supporting isochronous transfer secures the band for isochronous transfer, BANDWIDHT__ which is implemented by the isochronous resource manager is checked.
Check the value of the AVAILABLE register by a read or lock transaction. In addition, CHANNELS_AVA
Check the value of the ILABLE register to understand the bandwidth and the number of channels. This operation is performed to confirm the bandwidth remaining for asynchronous transfer. The IEEE 1394 protocol guarantees one band that can perform asynchronous transfer for the maximum data payload size within one cycle (125 μsec), but how much remaining band is used for isochronous transfer other than that. By confirming that, it is possible to grasp the number and size of packets that can be transferred within one cycle.

The acquired information is collectively transmitted to the data payload size setting processing unit 108 and used when determining the initial value of the packet size at the time of subsequent data transfer.

FIG. 3 is a flow chart of the data payload size setting process in this embodiment.

In step S301, when transferring a large amount of data, an initial value of the payload size at the time of transfer is set. A method of setting the initial value will be described later in detail with reference to the flowchart of FIG.

In step S302, the timer 109 is set to I
The EEE1394 driver 104 is activated. In this embodiment, the timer 109 is activated immediately before the request packet is transmitted, but it may be activated immediately after the request packet is transmitted.

In step S303, the request packet is transmitted. As described in step S302, the order of timer activation may be reversed. In this embodiment, S
This is a read transaction because the packet transfer is based on the assumption that a PC is the receiving node according to the BP-2 protocol. Print data is included in the data payload of the expected response packet.

In step S304, it is determined whether a response packet to the transmitted request packet has been received. Since it is actually a split transaction, the pending AC before the response packet is received.
I have received K, but I will omit the processing when I receive pending. When the corresponding response packet is received, the process proceeds to step S305, and when the response packet cannot be received (for example, when ACK_busy is received or split timeout occurs), the process proceeds to step S3.
Go to 10.

In step S305, the timer 109 started in step S302 is stopped upon receipt of the response packet. Link LS as timer 109
When using the split timeout monitoring timer built in I, there is a timer in which the timer 109 is automatically stopped at the same time as the reception of the response packet.

In step S306, the stopped timer 1
Figure out the count value of 09. This is to measure the time from startup to stop, but when using the timer 109 whose count value is automatically reset at the time of stop, the timer 109 is stopped by firmware and the value is confirmed.

In step S307, step S306
It is determined whether or not the timer value acquired in (1) exceeds the reference value allowed as the time from the transmission of the request packet to the reception of the response. If the timer value exceeds the reference value, the process proceeds to step S308, and if not, the process proceeds to step S309.

In step S308, the value of the data payload size at the time of transmitting the request packet is changed in response to the fact that it takes longer than expected to receive the response packet. Specifically, a value smaller than the currently set value is set.

Since the value indicating the time required until the response packet is received is larger than the allowable reference value, the following two can be assumed. One is that the bandwidth for asynchronous transfer is narrow, so it may take time because the bus right cannot be secured even though the receiving node is ready to send the response packet. It is possible that although the bus right is secured, it takes a long time because the processing of the receiving node is slow. In any case, the problem can be solved by reducing the data payload size.

In step S309, it is determined whether or not there is a request packet to be further transmitted. If the request packet still exists, the process returns to step S302 to repeat the process. If the data transfer has already been completed and there is no packet to be requested, the process ends.

In step S310, it is determined whether the receiving node is busy. If it is busy, the process proceeds to step S312. If not, for example, if an error occurs or split timeout occurs, the process proceeds to step S311.

In step S311, if the transaction is not completed due to a data error, split timeout, retry over, etc., the transaction is issued again at the application layer level. The number of application-level retries is not specified in the protocol, but it is a finite number. Although not shown in the flowchart, if the transaction is not completed even after the specified number of times, the process is interrupted as an error.

In step S312, in response to the fact that the receiving side node is busy, a retry process for transmitting the request packet again is performed.

In step S313, the number of times the retry packet is transmitted is counted.

In step S314, step S313
It is determined whether or not the value counted in step 3 has exceeded an arbitrary value N. The arbitrary value N is appropriately set in advance as a value serving as an index indicating the frequency of the number of retries.

In step S315, the value of the data payload size at the time of request packet transmission is changed in response to repeated retries. Specifically, a value smaller than the currently set value is set.

The occurrence of repeated retries is that data is requested with a payload size exceeding the processing capacity of the receiving side node. In that case, the problem can be solved by reducing the data payload size.

In step S316, it is determined whether a response packet for the transmitted retry packet has been received. It's actually a split transaction,
Although the pending ACK is received before the response packet is received, its processing is omitted. When the corresponding response packet is received, step S3
If the response packet cannot be received (for example, a split timeout occurs when ACK_busy is received), the process proceeds to step S317.

In step S317, it is determined whether or not the number of retries exceeds the specified number and retry over occurs due to repeated retry processing. If a retry over has occurred, the process advances to step S311 to end the transaction processing and perform application level retry processing. If the number of retries is within the specified number, the process returns to step S312 and the retry packet is transmitted again.

FIG. 4 is a flowchart of the data payload size initializing process in this embodiment, which is performed in step S301 of FIG. Based on the information acquired at the time of bus reset explained in FIG. 2, the initial value of the data payload size at the time of transferring a large amount of data is set.

In step S401, the bandwidth reserved for isochronous transfer is confirmed. Since this information has already been obtained in step S204, the content is confirmed.

In step S402, it is determined whether or not the bandwidth left for the node performing the asynchronous transfer is smaller than an arbitrary value. Here, for example, in addition to the bandwidth originally reserved for asynchronous transmission, a determination is made based on whether or not it is smaller than 1229, which is a bandwidth indicating a bandwidth that can perform another asynchronous transmission with the maximum payload size. The value used is arbitrary. If the remaining band is less than an arbitrary value (1229 in this case), go to step S403, and if not, go to step S40.
Go to 5.

In step S403, from the total number of nodes connected to the bus, the IEEE 1394 device 101 (transmission side node) intended to transfer a large amount of data, its reception side node, and the number of nodes performing isochronous transfer are calculated. Determine if the subtracted value is greater than any value. Here, the value to be compared is temporarily set to 2, but the value changes depending on the balance with the remaining band determined in step S402. Here, for example, when the total number of nodes connected to the bus 102 is 5 and there is one node that performs isochronous transfer, the value becomes 2 when 3 nodes including the IEEE 1394 device 101 and the receiving side node are subtracted. If the value thus obtained is greater than 2, then step S
If not, the process proceeds to step S405.

In step S404, step S402
When it is determined that there is not a sufficient bandwidth for asynchronous transfer, and there is a node other than the IEEE 1394 device 101 and the receiving side node that has a high possibility of performing large-capacity data transfer using asynchronous transfer, the IEEE
A value smaller than the maximum data payload size that can be received and transmitted by the E1394 device 101 is set to IEEE1.
The payload size is set when data is transferred to the 394 device 101, and the initial value setting process ends.
For example, when the maximum payload size is 2048 bytes, 1024 bytes is set as the payload size during transfer.

At step S405, step S402.
When it is determined that there is a sufficient band for asynchronous transfer in step S404, or when a large band is secured for isochronous transfer in step S404, there are few devices that perform large-capacity data transfer by asynchronous transfer, and a bus is secured for the transfer. When it is determined that there is no inconvenience, the maximum data payload size that can be received and transmitted by the receiving side node is set as the payload size when performing data transfer with the receiving side node, and the initial value setting process ends.

In the present embodiment, the information of the node connected to the bus and the response of the receiving side node are taken into consideration as means for realizing the function. Although the effect of setting the initial value based on this is inferior, the same effect can be realized.

As described above, according to the configuration of the present invention, it is possible to reduce the transfer time when transferring a large amount of data. Moreover, the performance of the entire system can be improved by effectively using the bus by increasing the number of transmissions and reducing the number of retries.

[0080]

Other Embodiments The object of the present invention is to supply a storage medium (or recording medium) recording a program code of software for realizing the functions of the above-described embodiments to a system or apparatus, and to supply a computer of the system or apparatus. It is needless to say that it can be achieved by (or CPU or MPU) reading and executing the program code stored in the storage medium. In this case, the program code itself read from the storage medium realizes the functions of the above-described embodiments, and the storage medium storing the program code constitutes the present invention. Further, by executing the program code read by the computer, not only the functions of the above-described embodiment are realized, but also an operating system (OS) running on the computer is executed based on the instruction of the program code. It goes without saying that a case where some or all of the actual processing is performed and the functions of the above-described embodiments are realized by the processing is also included.

Further, after the program code read from the storage medium is written in the memory provided in the function expansion card inserted into the computer or the function expansion unit connected to the computer, based on the instruction of the program code. , The CPU provided in the function expansion card or the function expansion unit performs some or all of the actual processing,
It goes without saying that the processing includes the case where the functions of the above-described embodiments are realized.

When the present invention is applied to the above-mentioned storage medium, the storage medium stores the program code corresponding to the flowcharts shown in FIGS. 2 to 4 described above.

[0083]

As described above, according to the present invention, the data payload size of the packet sent on the bus can be set to an appropriate data payload size. As a result, it is possible to shorten the transfer time when transferring a large amount of data, and to reduce the number of transmissions and retries.
The bus can be effectively used, and the performance of the entire system can be improved.

[Brief description of drawings]

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

FIG. 2 is a flowchart of information acquisition processing performed at the time of bus reset in the embodiment of the present invention.

FIG. 3 is a flowchart of a data payload size setting process according to the embodiment of the present invention.

FIG. 4 is a flowchart of a data payload size initialization process according to the embodiment of the present invention.

[Explanation of symbols]

101 IEEE 1394 device (request packet transmission side node) 102 IEEE 1394 bus 103 IEEE 1394 I / F control unit 104 IEEE 1394 driver 105 node controller 106 application layer 107 application 108 data payload size setting processing unit 109 timer 110 printer function

Claims (31)

[Claims] 1. A communication device capable of transmitting and receiving data in isochronous transfer and asynchronous transfer, comprising communication means for transmitting and receiving data to and from an external device connected via a communication interface, and in asynchronous transfer. When transmitting and receiving data, a determining means for determining the responsiveness of the external device of the communication destination, and a changing means capable of changing the data payload size at the time of transmitting and receiving in asynchronous transfer according to the determination by the determining means. A communication device having. 2. An acquisition unit that acquires information about a transfer band used in asynchronous transfer on a bus to which the communication device is connected via the communication interface, and information about a transfer band acquired by the acquisition unit. And a setting unit configured to set the data payload size based on the above, wherein the operations of the acquisition unit and the setting unit are performed prior to the operations of the determination unit and the changing unit. The communication device described. 3. The acquisition means acquires the information on the transfer band by reading a configuration ROM and a control and status register of each external device connected to the bus. 2. The communication device according to item 2. 4. The information relating to the transfer band includes the number of external devices performing isochronous transfer, and the isochronous transfer bandwidth and the number of channels acquired by the external device. The communication device according to item 3. 5. The communication device according to claim 3, wherein the information regarding the transfer band includes the number of external devices connected to the bus. 6. The acquisition means acquires the information on the transfer band by acquiring a self-ID packet transmitted from each external device connected to the bus after the bus is reset. Claims 2 to 5
The communication device according to any one of 1. 7. The setting means sets the maximum transferable data payload size when the information regarding the transfer band satisfies a predetermined condition, according to any one of claims 2 to 6. The communication device described. 8. The communication device according to claim 7, wherein the predetermined condition is that a band left for asynchronous transfer is larger than a predetermined band. 9. The predetermined condition is, in addition to the communication device,
9. The communication device according to claim 7, wherein the number of external devices connected to the bus that performs asynchronous transfer is less than a predetermined number. 10. The determining means compares the minimum time required to complete a transaction performed by the communication device with the time required for a response by the external device at the communication destination. The communication device according to any one of 1 to 9. 11. The time required for the external device of the communication destination to respond is a time required for the communication device to receive a response packet after transmitting a request packet to the external device of the communication destination. Claim 1
0. The communication device according to item 0. 12. The communication device according to claim 10, further comprising a timer for measuring a time required for the external device of the communication destination to respond. 13. The communication device according to claim 1, wherein the changing unit reduces the data payload size value when the external device of the communication destination has low responsiveness. 14. The communication device according to claim 1, wherein the communication unit complies with the IEEE 1394 standard. 15. A communication method in a communication device, which is capable of transmitting and receiving data by isochronous transfer and asynchronous transfer and has a communication means for transmitting and receiving data to and from an external device connected via a communication interface. Therefore, when data is transmitted / received by asynchronous transfer, the data payload size at the time of transmission / reception in asynchronous transfer is changed according to the determination step of determining the response of the external device of the communication destination and the determination in the determination step. A communication method comprising a possible changing step. 16. An acquisition step of acquiring information on a transfer band usable in asynchronous transfer on a bus to which the communication device is connected via the communication interface; and a transfer band acquired in the acquisition step. 16. A setting step of setting the data payload size based on information, wherein the acquisition step and the setting step are performed prior to the determining step and the changing step.
The communication method described in. 17. The information about the transfer band is obtained by reading a configuration ROM and a control and status register of each external device connected to the bus in the obtaining step. 16. The communication method according to 16. 18. The information on the transfer band includes the number of external devices that perform isochronous transfer, and the bandwidth and the number of channels for isochronous transfer acquired by the external device. 17. The communication method according to item 17. 19. The communication method according to claim 17, wherein the information on the transfer band includes the number of external devices connected to the bus. 20. In the acquisition step, the information regarding the transfer band is acquired by acquiring a self-IM packet transmitted from each external device connected to the bus after the bus is reset. Claim 16
20. The communication method according to any one of 19 to 19. 21. In the setting step, when the information regarding the transfer band satisfies a predetermined condition, the maximum transferable data payload size is set. The communication method described. 22. The communication method according to claim 21, wherein the predetermined condition is that a band left for asynchronous transfer is larger than a predetermined band. 23. The predetermined condition is that, in addition to the communication device, the number of external devices connected to the bus that performs asynchronous transfer is smaller than a predetermined number. Communication method. 24. The determining step compares a minimum time required for completing a transaction performed by the communication device with a time required for a response by the external device of the communication destination. The communication method according to any one of 15 to 23. 25. The time required for the external device of the communication destination to respond is a time required for the communication device to receive a response packet after transmitting a request packet to the external device of the communication destination. Claim 2
4. The communication method according to 4. 26. The communication method according to claim 24, further comprising a time counting step of measuring a time required for the external device of the communication destination to respond. 27. The communication method according to claim 15, wherein the data payload size value is reduced in the changing step when the response of the external device of the communication destination is low. 28. The communication means complies with the IEEE 1394 standard.
The communication method according to any one of 1. 29. A program executable by an information processing device, the information processing device executing the program comprising:
A program that functions as the communication device according to any one of claims 1 to 14. 30. A program executable by an information processing device, having a program code for implementing the communication method according to any one of claims 15 to 28. 31. A storage medium storing the program according to claim 29 or 30.