## Physical Device Driver Reference

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### Obtaining a Logical ID

During its initialization, an ABIOS device driver must obtain the Logical ID (LID) for its physical device. The allocation of a LID is managed by the operating system. This ensures that the physical device driver receives a unique LID for its device type. The operating system provides a DevHlp_LIDEntry to obtain the LID for a device driver. The DevHlp_ GetLIDEntry finds the LID for the specified Device ID and allocates it to the calling device driver.

An ABIOS device driver maps its device name to a unit within a LID. It receives a DEINSTALL request for its device name. This implies a single unit of a LID. To honor the DEINSTALL request, it must relinquish the LID through use of the DevHlp_FreeLIDEntry at deinstall time.

Note: To release a LID means to release all units under that LID. For a LID that has multiple units, the physical device driver must discontinue support of all units under the LID. If multiple units correspond to multiple device headers in the device driver data segment, the device driver must note which device header corresponds to each unit in the DEINSTALL LID and discontinue support.

The operating system prohibits access the LID for system services. Operating system management of LID access is similar to the management of hardware interrupt levels or I/O ports.