Texas Instruments OMAP5912 Reference Manual page 1355

2.8 USB Host Controller Access to System Memory
2.9 Physical Addressing
Figure 2. Relationships Between Virtual Address Physical Address
SPRU761A
The USB host controller must have access to system memory to read and write
the OHCI data structures and data buffers associated with USB traffic. The
OMAP5912 OCPI bus allows the USB host controller to access OMAP5912
system memory, as shown in Figure 1.
Transactions on the OMAP5912 OCPI bus use physical addresses, so all
system memory accesses initiated by the USB host controller must use
physical addresses. The OMAP5912 MPU can be configured to use virtual
addressing. In this case, MPU software manipulates virtual addresses that
may or may not be identical to physical addresses. When virtual addressing
is used, system software must perform the appropriate virtual address to
physical address and physical address to virtual address conversions when
manipulating the USB host controllers data structures and pointers to those
data structures.
Figure 2 shows the MPU virtual address to physical address conversion.
Processor
physical
address
USB Host Controller
0x00000000
Processor
MMU
0xFFFFFFFF
Processor
virtual
address
Universal Serial Bus (USB) 63