USB Host Layer Transfers Number 

This constant defines the maximum number of transfers that the host layer should handle. The choice of this constant depends on the nature of devices that the USB Host application must support. Atleast two transfers are needed per pipe in the system. If the number of transfers provisioned in the system are insufficient, the USB Host will decline transfer request citing a busy status. This will affect the speed performance of the system.

#define USB_HOST_TRANSFERS_NUMBER 

None.

A USB Host application will support an MSD device and a CDC Device. The total number of pipes needed in the system are 7. The USB_HOST_TRANSFERS_NUMBER constant should be atleast 14 (2 per pipe). Specifying a larger number will enable more transfers to be queued but will also require more data memory.