## Physical Device Driver Reference

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### Use of Physical Addresses - PhysToUVirt

Physical device drivers that use DevHlp_PhysToUVirt will notice changes in these areas:

Returned offset (in BX) can no longer equal 0.

The OS/2 I/O Subsystems and Device Support Device Drivers (erroneously) stated that the result found in BX, on return from the call to PhysToUVirt, would always be 0.

In OS/2 2.1, BX is not always equal to 0 on return from PhysToUVirt.

Mapped areas that are greater than 60KB might not be fully mapped if their beginning offset is greater than 0. For example, a 64KB object that begins at n bytes offset from a 4KB page boundary results in a segment/descriptor that has a length of 64KB-n.