## Display Device Driver Reference for OS/2

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### Limitations of the PMI

The following limitations exist in the PMI:

.PMI does not provide a graphical interface.

.PMI does not provide a means of accessing addresses that are internal to the video controller and are not mappable into the CPU space.

Save and Restore Hardware State Services have certain limitations (see " Save and Restore State" in this chapter).

.PMI does not provide the means to manipulate certain video parameters outside the context of the SetMode section.

.PMI does allow, and it requires, indirect management of all of the parameters within the Mode Set sections. For example, there are no services for the manipulation of the hardware cursor or RAMDAC outside the context of a mode set. These services are an integral part of the SetMode.

Programming of the monitor timing is considered a special case. It is an integral part of the SetMode, but it also can be independently invoked, if the .PMI file defines a SetMonitorTimings section. The same is true for manipulation of the active display size. If the PMI file contains a TuneDisplay section, this manipulation is offered independently.

Port descriptions have some limitations, as follows:

-Ports that require double or triple indirection cannot be adequately described in the PMI language.

-I/O addresses that serve as latches, or flip-flops, cannot be successfully described.

-There are no provisions for describing port addresses that define different registers depending on the read or write access.

These limitations have an influence on the level and success of the adapter virtualization using the system-provided virtual driver. See [TrapRegs] in PMI Sections.