Electrical computers and digital data processing systems: input/ – Intrasystem connection – Bus access regulation
Reexamination Certificate
1998-09-10
2001-06-19
Beausoleil, Robert (Department: 2732)
Electrical computers and digital data processing systems: input/
Intrasystem connection
Bus access regulation
C710S120000, C709S209000, C709S227000, C709S228000, C709S250000
Reexamination Certificate
active
06249829
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a communication bus system according to the precharacterizing part of claim
1
.
The invention also relates to a execution station for use in such a communication bus system.
The IEEE 1394 bus system is a communication bus system (which will be referred to as a 1394 system) which can be applied to connect stations such as TV sets and videorecorders. Chapter 8 of the IEEE 1394 standard describes that an execution station has a number of control status registers (CSR's). The contents of several of those CSR's can be modified in response to request packets from all of the several requesting stations.
To prevent errors, the requesting station which sends a request packet should be able to determine reliably whether the command has actually been executed, especially if the effect of repeated execution of the command differs from that of single execution (e.g. in case of an “increase TV channel number” command or a “reserve capacity” command). When the execution station contains a status register that is affected by execution of the command and that can be read by a command from the requesting station, it is possible, in principle, to determine whether the command has been executed by verifying the contents of the status register. However, verifying the contents of the status register to detect execution does not work reliably when the bus system contains more than one requesting station that can send a request packet with a command that affects the same status register.
In 1394, the execution station after execution of a command returns a response packet to the requesting station which issued the request packet in response to which the command was executed. This allows the requesting station to determine whether the command has been executed, but it does not work when the requesting station fails to receive the response packet.
SUMMARY OF THE INVENTION
It is an object of the invention to provide for a more reliable way of determining whether the command has actually been executed.
According to the invention, in the communication bus system according to the invention is characterized by the charactering part of claim
1
. By reading command execution information each particular requesting station can verify whether a command requested by it has been executed. Later execution of commands requested by other requesting stations does not affect the command execution information for the particular requesting station and therefore does not affect the reliability of verification.
The communication bus system according to the invention has an embodiment as described in claim
6
. In this embodiment a particular requesting station can issue several request packets requesting execution of different types of command and verify whether the corresponding commands have been executed after all the request packets have been issued. This means that the request packets can be issued rapidly one after the other as a coherent operation, without interruption for verification. In a 1394 system, each type of command for example affects a different CSR, and the communication bus system keeps information for each particular requesting station about the last executed modification of each of the CSR's that that particular requesting station has requested.
Several forms of command execution information may be stored. If the requesting station includes a respective packet identification in each packet, then the stored command execution information may contain that packet identification. This makes it possible to check on the execution of any command at any time. The stored command execution information may contain information about the status of the execution station immediately after execution of the command or of results produced by the execution. This makes it possible for the requesting station to analyze the execution of the command in any desired amount of detail, for example in more detail than in a standard response from the execution station. Any such command execution information may be kept stored for all of the request packets received by the execution station, or for a predetermined number of request packets for which the commands have been most recently executed. Thus older commands can also be analyzed.
The command execution information may be stored in several ways. A respective predetermined storage area may be allocated in the execution station for each requesting station. When a command is executed in response to a request packet from a particular requesting station, the executing station may use the command execution information for that execution to overwrite command execution information stored in the storage area allocated to that particular requesting station. Thus, the storage area always contains the command execution information for the most recently executed command for that particular station (or initiation information, stored by the execution station before receiving any request packet). The storage area allowed to each particular station, may be subdivided into storage subareas for different types of commands, the execution station overwriting only the storage subarea for the command being executed.
In a preferred embodiment only one logical bit per command type is stored for each requesting station respectively. When the execution station has successfully executed a command in response to a request packet received from a particular requesting station, the execution station sets the logical bit for that particular requesting station (and for the type of command, if more than one type of command is recorded). In this case the executing station must also be capable of resetting the logical bit, preferably in response to a signal from the particular requesting station. In the 1394 system this signal may for example be generated when the particular requesting station reads out the CSR whose modification is recorded by the logical bit.
Readout of the command execution information is preferably triggered by a readout packet transmitted by the requesting station to the execution station via the bus interconnection. In response to this readout packet, the execution station determines from which requesting station the readout packet is issued, reads out the command execution information stored for that requesting station and sends a status packet derived under control of that command control information to the requesting station via the interconnection bus.
Preferably the memorization of command execution information is combined with the transmission of response packets by the execution unit. This gives the requesting station the option to check on critical execution of commands if no response packet is received.
REFERENCES:
patent: 5953511 (1999-09-01), Sescila
patent: 5961623 (1999-10-01), James
patent: 6088728 (2000-07-01), Bellemore et al.
“The IEEE 1394 Standard”, Chapter 8, pp. 199-242.
Bloks Rudolf H. J.
Wong Calto
Beausoleil Robert
Phan Raymond N.
Piotrowski Daniel J.
U.S. Philips Corporation
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