JPH0237450A - Channel device - Google Patents

Abstract

PURPOSE:To suppress the occurrence of command overrun at the time when the command of a chained CCW is a branch instruction (TIC) by eliminating a need of CCW fetch when the destination of the TIC is the just preceding CCW. CONSTITUTION:A TIC decision circuit 26 decides a TIC to send a TIC decision signal, and meanwhile, a comparing circuit 25 compares the preceding CCW address in a preceding CCW address register 24 with the TIC destination CCW address in an execution CCW register 22 to send a coincidence signal. When the TIC decision circuit 26 indicates the TIC and the comparing circuit 25 indicates the coincidence, a fetch control circuit 27 instructs a selecting circuit 21 to select the output of a preceding CCW register 23, and the next CCW is not fetched but the CCW in the preceding CCW register 23 is stored in the execution CCW register 22 through the selecting circuit 21. Then, an I/O 30 is started through a command executing part 28 to execute the command. Since the next CCW is not fetched from a memory 10 but the CCW in a channel device 20 is used in this case, the time required for command sending is shortened. Thus, command overrun is prevented.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a channel device.

[Prior Art] When a central processing unit (hereinafter abbreviated as CPU) instructs a channel device (hereinafter abbreviated as CH) to execute a channel program, it specifies the start address of the channel program and activates it.

FIG. 4 is a time chart showing the conventional operation of the main storage device, channel device, and input/output device after this. C to Ilo
Pass the command during CW. Ilo receives commands and executes them. After that, when the CH receives the command completion report from Ilo, it checks the completion status, and if there is no abnormality and the CCW indicates a chain command, then it fetches the CCW from the memory,
Pass the command to Ilo and continue its execution. At this time, the chained CCW's command is transmitted to the other CCW.
If it is a branch instruction (hereinafter abbreviated as TIC) that branches to , the CCW fetch is performed from the memory again and the command is passed to Ilo.

[Problem to be solved by the invention] In the conventional channel device described above, the CCW command is
If the IC runs out, two CCW fetches from memory (TIC and TIC destination CCW) are required for one I10 startup, and after receiving the end of the command from Ilo, the next There is a drawback that it takes too much time to issue a command, which exceeds the Ilo monitoring time, resulting in a command overrun.

[Means for Solving the Problems] The channel device of the present invention has an execution CCW that holds the channel command word currently being executed.
holding means; a previous CCW holding means for holding a channel command word executed immediately before the currently executed channel command word; and an address of a channel command word executed orthogonally to the currently executed channel command word; a previous CCW address holding means for holding a previous CCW address; a comparing means for comparing a data address part of a channel command word held in the execution CCW holding means with an address held in the surface CCW address holding means; branch determining means for determining whether a command part of a channel command word held in the CCW holding means is a branch instruction; and when the branch determining means indicates a branch and the comparing means indicates a match, and a fetch control circuit that transfers the CCW in the CCW holding means to the execution CCW holding means and uses it as a next execution channel command word.

[Operation] Generally, TIC often branches to the CCW immediately before Tic. Therefore, if the most recently executed CCW and its address are retained and a branch is made just before the TIC, the most recently executed CCW retained in the channel device is used, so the time required to send the command is Becomes shorter.

[Embodiments] Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of the channel device of the present invention.

The channel device 20 is located between the memory 10 and the l1030, and is connected to the memory 10 by the output of the fetch control circuit 27.
and the output of the previous CCW register 23 and supplies the output to the execution CCW register 22; and an execution CCW register 22 that holds the CCW currently being executed in the channel device 20. , an execution CCW register 23 that holds the CCW executed before the currently executed CCW, and a previous CCW register 23 that holds the CCW address of the CCW held in the previous CCW register 23.
Compare the CW register 24, the address of the last executed CCW, and the data address part of the currently executed CCW,
a comparison circuit 25 that sends a match signal to the fetch control circuit 27 if the execution CCW is TIC, and a TIC that judges whether the execution CCW indicates TIC and sends a TIC determination signal to the fetch control circuit 27 if it is TIC a TIC determination circuit 26 that sends a determination signal to the fetch control circuit 27;
When the comparison circuit 25 outputs a match signal and the TIC determination circuit 26 outputs a TIC determination signal, the selection circuit 21 is instructed to select the output of the previous CCW register 23, and the memory 10 is does not issue a CCW fetch request, otherwise CCW is sent to memory 10.
a fetch control circuit 27 that issues a CW fetch request and instructs the selection circuit 21 to select the output of the memory 10;
It includes a command execution unit 28 that instructs the 11030 to execute a command.

FIG. 2 is a diagram showing the format of CCW in this embodiment.

The CCW is composed of a command section, a flag section, a count section, and a data address section, and when the command is a TIC, the data address becomes the CCW address of the TIC destination.

FIG. 3 shows the channel device 20 and l1030 of this embodiment.
3 is a time chart showing the operation of FIG.

Next, the operation of this embodiment will be explained with reference to FIG.

When the CPU (not shown) instructs the channel device 2o to execute a channel program, the CPU fetches the CCW from the specified address and stores it in the execution CCW register 22 through the selection circuit 21.

Then, the l1030 is activated through the command execution unit 28 to execute the command. When the command is executed and then receives the exit status from l1030,
Check completion status. If there is no abnormality in the end status and the CCW indicates a chain command, execute C.
The CCW stored in the CW register 22 is stored in the current CCW register 23, and the execution CCW address is stored in the previous CCW address register 24. Then, the next CCW is fetched and stored in the execution CCW register 22 through the selection circuit 21.

If this CCW is not TIC, it activates l1030 through the command execution unit 28 and executes the command.

CCW is TIC, and previous CCW address and TIC destination C
Consider the case where the CW address and the CW address do not match.

When the CCW in the execution CCW register 22 is TIC, the TIC determination circuit 26 determines that it is TIC, and
A C judgment signal is being sent. On the other hand, the comparison circuit 25
The previous CCW address in the CW address register 24 and the TIC destination CCW address in the execution CCW register 22 are compared, and since they do not match, no match signal is sent. The fetch control circuit 27 issues a CCW fetch request to the memory 10 since the TIC determination circuit 26 indicates TIC, but the comparison circuit 25 indicates no match. after that,
CCW from memory 10 is executed through selection circuit 21
The command is stored in the W register 22 and executed through the command execution unit 28.

Next, if the CCW is TIC and the previous CCW address and TI
Consider the case where the C destination CCW address matches (the time chart in FIG. 3 shows this case). This is generally the case when CCW is TIC.

The TIC determination circuit 26 determines that it is TIC, and the TI
A C judgment signal is being sent. On the other hand, the comparison circuit 25
The previous CCW address in the CW address register 24 and the TIC destination CCW address in the execution CCW register 22 are compared, and a match signal is sent out. Fetch control circuit 2
7 indicates TIC by the TIC determination circuit 26, and the comparison circuit 25
indicates a match, so the selection circuit 21 is instructed to select the output of the previous CCW register 23, and the CCW in the previous CCW register 23 is passed through the selection circuit 21 to the execution CCW register 22 without fetching the next CCW. Store. Then, the l1030 is activated through the command execution unit 28 to execute the command. In this case, the state CCW is not newly fetched from the memory 10 and the CCW inside the channel device 20 is
Since W is used, the time required to send a command is short.

Note that the present invention can also be implemented by a microprogram in a channel device using a microprogram control method.

[Effect of the invention] As explained above, the present invention enables the TIC destination to
By eliminating the need to fetch the CCW in the case of
Even if the chained CCW command is a TIC, there is an effect of suppressing the occurrence of a command overrun.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the channel device of the present invention, FIG. 2 is a diagram showing the format of CCW in this embodiment, and FIG. 3 is a diagram showing the operation of the channel device 20 and l1030 of this embodiment. FIG. 4 is a time chart showing the operation of the conventional channel and Ilo. IO...Memory, 20...Channel device, 30...-Ilo, 21...Selection circuit, 22...Execution CCW register, 23...Previous CCW register, 24...Previous CCW address register , 25... Comparison circuit, 26... TIC determination circuit, 27... Fetch control circuit, 28... Command execution unit.

Claims (1)

[Claims] 1. In a channel device that is located between a memory and an input/output device and controls the execution of a channel command word, an execution CCW that holds a channel command word that is currently being executed.
holding means; a previous CCW holding means for holding a channel command word executed immediately before the currently executed channel command word; and a previous CCW holding means for holding the address of the channel command word executed immediately before the currently executed channel command word. previous CCW address holding means for holding the previous CCW address; comparison means for comparing the data address part of the channel command word held in the execution CCW holding means with the address held in the previous CCW address holding means; branch determining means for determining whether or not the channel command word command part held in the holding means is a branch instruction; and when the branch determining means indicates a branch and the comparing means indicates a match, the previous CCW is retained. A channel device comprising: a fetch control circuit that transfers a CCW in the means to the execution CCW holding means to use it as a next execution channel command word.