| 摘要 |
An I/O command block chain structure allows simultaneity of execution, provides a mechanism to inhibit and enable execution of an individual I/O command block, and a mechanism for establishing precedence in the sequence of execution of the I/O command blocks. After the chain is configured and stored in a memory, an I/O command in an I/O command block in the chain is executed first. Upon completion of execution of the I/O command, a chain manager is executed. The chain manager examines the chain control field in an I/O command block pointed to by a next block pointer in the I/O command block, and decides what to do with the next I/O command block based on the state of its chain control byte. The chain manager may post completion of the chain, or may simply decrement the progress count in a following I/O command block on the chain path, and return to an idle loop. Alternatively, the chain manager may decrement the progress count in a following I/O command block on the chain path, enable the following I/O command block for execution, and return to an idle loop.
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