The USB MSD Host Client Driver provides the top level block storage driver with an easy to use, event driven, interface to transport the block storage command and data between the block storage command driver library and a compliant mass storage device. The USB MSD Host Client Driver in the MPLAB Harmony USB Host stack immediately supports mass storage devices that advertise support of the SCSI command set. Indeed, most of the commercially available USB storage devices such as USB pen driver and USB card readers respond to SCSI command requests. 

The process of initializing the SCSI block storage driver library when a device is attached is performed automatically, by the USB MSD Host Client Driver. This does not require user application intervention. The following sections describe the TPL table design (application responsibility) and USB MSD Host Client Driver data transfer function (typically called by the SCSI block storage driver library).