## Display Device Driver Reference for OS/2

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### Level 0 Physical Device Driver Interfaces

The strategy portion of the Level 0 physical device drivers that can be a component of any video device handler is called to handle I/O requests through a request packet interface with the OS/2 kernel. The strategy routine executes at task-time as a result of an application VIO request. The strategy routine is called with ES:BX pointing to the request packet ( the pointer is valid in both a DOS session and an OS/2 session). Only three command codes (passed in the request packet) are required to be supported by a video device driver. For any other command code the physical device driver does not support, the physical video device driver must return Unsupported Command and Done in the request packet status field.

The following are the physical device driver commands that are supported by the physical video device driver (the command codes are in parentheses):