## Storage Device Driver Reference

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### SCSI Command Linking With ASPI

ASPI provides the ability to use SCSI linking to guarantee the sequential execution of several commands. This feature requires that the involved target(s) support SCSI linking.

To use SCSI linking, a chain of SRBs is built with the SRB link pointer used to link the elements together. The link bit should be set in the SCSI request flags byte of all SRBs except the last in the chain. When a SCSI target returns indicating that the linked command is complete, the next SRB is immediately processed, and the appropriate CDB is dispatched. When using SCSI linking, make sure that the linking flags in the SCSI CDB agree with the link bit in the SCSI request flags. Inconsistencies can cause unpredictable results. For example, setting the CDB up for linking but failing to set the link bit may result in a random address being used for the next SRB pointer.

Any error returned from the target on a linked command will break the chain . Note that if linking without tags is used, as defined in SCSI, posting may not occur on any elements in the chain until the chain is complete. If you have the post bit set in each SRB's SCSI request flags byte, then each SRB's post routine will be called.

Note: Do not use SCSI linking. Many SCSI targets, as well as SCSI host adapters, do not handle SCSI linking and will not work with your ASPI module.