Fujitsu MBA3073RC, MBC2036RC Command Queuing Function, READ, Read EXTENDED, WRITE, Write Extended

Command Processing

2.3 Command Queuing Function

The HDD is equipped with the command queuing function. Through command queuing, the HDD can receive multiple commands in advance and can execute them.

Through the tagged queuing function, the HDD can receive multiple commands from the same INIT or from different INITs until the command queue is full. The number of commands that can be received by the HDD is 128 per HDD, without relation to the INIT. When the HDD receives a new command, if the command queue is full, the new command is responded to with the TASK SET FULL status.

The HDD controls the command queue, but it is possible for the INIT to delete commands from the queue by adding a command.

When the HDD adds a command to the queue, an INIT can specify the TASK ATTRIBUTE of the CMND frame to give the HDD instructions about the execution order of commands or the command to be executed next. There are three TASK ATTRIBUTEs: ORDERED, HEAD OF QUEUE, and SIMPLE.

When ORDERED is specified, the HDD executes commands in the order they are received. All the commands received with SIMPLE specified before a command received with ORDERED specified are, regardless of the INIT, executed before the command received with ORDERED specified. All the commands received with SIMPLE specified after a command received with ORDERED specified are executed after the command received with ORDERED specified.

Commands received with a HEAD OF QUEUE are registered at the top of the queue for waiting execution. The HDD does not interrupt the current command execution and executes them after completion of current command execution. When commands with the HEAD OF QUEUE are received continuously, the HDD first executes the command which was received last.

If "0000" or "0001" is specified by the Queue algorithm modifier in the control mode page, the HDD performs reordering processing of commands with respect to commands issued together with the SIMPLE. Reordering processing is performed with the purpose of reducing the total processing time in command processing.

∙Conditions for Reordering:

If commands which are objects of reordering are issued by an INIT which permits reordering together with a SIMPLE.

∙Commands which are Objects of Reordering:

READ, READ EXTENDED, WRITE, WRITE EXTENDED

If the INIT permits command reordering processing, the HDD changes the command processing order. It is necessary for the INIT to control concerning the validity of data.

110 C141-C013