Chapter 6. SCSI Miniport Drivers

SCSI miniport drivers are HBA-specific but OS-independent. That is, each miniport driver links itself against the SCSI port driver and calls only the port driver's ScsiPortXxx routines to communicate with the system. HBA miniport drivers can be compiled to run on machines running Windows 95 or Windows NT. Each platform provides an OS-dependent port driver that exports the ScsiPortXxx routines.

Every SCSI miniport driver must have at least the following system-defined routines:

• DriverEntry to initialize the miniport driver
• HwFindAdapter to determine how (or whether) driver-supported HBA(s) are configured in the machine
• HwInitialize to initialize the HBA(s)
• HwStartIo to start operations on the HBA for an incoming request
• HwResetBus to handle bus-reset requests

Depending on the HBA and the driver designer, SCSI miniport drivers also can have any or all of the following system-defined routines:

• HwInterrupt to handle HBA-generated interrupts, which is optional if and only if the miniport manages all I/O operations on its HBA by polling

However, using polling exclusively has an adverse effect on a miniport's performance and on its HBA's I/O throughput.

• HwDmaStarted to set up an HBA transfer after the system DMA controller has been programmed by the port driver
• HwDisableInterruptsCallback and HwEnableInterruptsCallback to handle deferred I/O processing if a particular operation takes a long time
• HwTimer to time operations on the HBA that require long delays

  A miniport should have a HwTimer routine if it has no HwInterrupt routine so it can use the HwTimer routine for efficient polling of the HBA.

• HwAdapterState, defined for compatibility with future MS-DOS versions

The following sections describe the requirements for and functionality of each of these miniport driver routines. For reference information about the services the SCSI port driver offers to a miniport driver, see Introduction to SCSI Port Driver Services Reference.

For a description of the error-handling requirements for SCSI miniport drivers, see Error Handling.