JPS594044B2 - Channel relocation mechanism - Google Patents

Description

[Detailed description of the invention] The present invention relates to a channel relocation mechanism.

The channel relocation mechanism operates the channel device while converting the channel and program written in virtual addresses into real addresses. Channel relocation operations are performed by a channel lookup buffer.

The channel index buffer contains virtual data addresses, virtual command addresses, and segments of subchannels sent at the start of I/O. It has a virtual address stack that holds table origin words, etc. A channel operation is initiated by execution of a start I/O (SIO) instruction that transfers a channel address word (CAW) from real storage to the channel; , where a virtual address to real address translation is performed for main memory access.

The real address obtained by the translation is held in the unit control word (UCW), and the corresponding virtual address and the upper part of the real address are held in the virtual address stack. When a channel program is initiated, data addresses are fetched sequentially by incrementing by eight.

If the data address does not cross a page boundary,
There is no need to translate virtual addresses to real addresses on each data retrieval operation. The high portions of the virtual and real addresses are therefore held in the virtual address stack and combined with the byte portion of the new data address to provide the new real address. The same is true for the command address used to retrieve the channel command word (CCW). If a data address crosses a page boundary and a page fault occurs during address translation, the channel raises a page fault interrupt, notifying the I/O supervisor to make the required page available, and The channel program is recovered by restarting the 510 instruction by the post-possible error recovery program.

With this method, it is possible to check whether there is a page fault for the first time when the data address crosses the page boundary, and there are the following problems. (1) When data transfer spans many pages, there is a possibility that a page failure will occur every time at a page boundary, resulting in a large overhead.

(2) If a page failure occurs during data block transfer, when data transfer is restarted, data must be transferred again from the beginning of the data block, resulting in a large overhead.

An object of the present invention is to provide a channel relocation device which eliminates the above-mentioned conventional problems and has the effect of being able to detect page faults before data transfer. .

A feature of the present invention is that the pages required by the channel for data transfer are calculated in advance and a page fault check is performed.

Next, embodiments of the present invention will be described in detail using the drawings. The figure shows a device for knowing in advance the page boundaries of a channel relocation mechanism, which is an embodiment of the present invention. CCWl holds the start address of the main storage device to which data should be transferred and the number of bytes to be transferred. This start address and the number of transferred bytes are added using adder 2 to obtain the final address of data transfer. The selectors 3 and 4 select the upper 12 bits of the first page address and the last page address of the data transfer, and the adder 5 subtracts them to find the number of pages required for the data transfer. Based on the information on the first page address and the required number of pages, it is possible to check for page failures before data transfer. This prevents page failures from occurring during data transfer and reduces software overhead due to page failures. It is possible to reduce overhead such as data retransfer and improve the efficiency of a computer using a channel relocation mechanism.

[Brief explanation of the drawing]

The figure is a block diagram showing one embodiment of the present invention. 1... Channel command word, 2... Adder, 3... Selector, 4... Selector, 5... Adder.

Claims (1)

[Claims] 1. In a channel relocation mechanism used in a data processing system that operates on a virtual memory method, the start address of the main memory to which data is to be transferred, the number of bytes to be transferred, and the number of bytes to be transferred, which are held in the channel command word, are held before data transfer begins. A channel relocation mechanism is provided with a device for detecting pages used by a channel based on the above, and detects page faults for all pages required for data transfer prior to data transfer.