## Physical Device Driver Reference

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### Managing System Resources

When a device driver allocates resources, it specifies the level of sharing that the driver is willing to accept. The level of sharing selected depends on the characteristics of the hardware, such as its ability to coordinate usage of IRQ or DMA channels with other adapters, as well as the importance of other functions that may need the same IRQ level. Resources are allocated on a first-come first-serve basis.

If a driver requests a resource that has been previously allocated to another driver, then the sharing mode selected by the earlier driver is used to determine if the new driver's request will be granted.

The following resource sharing options are available:

EXCLUSIVE The resource (such as the I/O Port and DMA Channel) is committed to the owner until it is explicitly released. Any other requests for this resource will be denied.

SHARED The resource will be granted to any requester that also requests the resource as shared. This implies that the users of the resource can use it at any time without interfering with each other. An example of a shared resource would be a shared interrupt on a Micro Channel* or EISA bus machine.

MULTIPLEXED The resource will be granted to any requester that also requests the resource as multiplexed. Multiplexed (unlike shared) implies that only one owner can actively be using the resource and that there is explicit notification between owners to control which requester is using the resource. In general, this sharing protocol is private to the multiplexed resource.

GRANTYIELD The resource will be granted to any requester that also requests the resource as GRANTYIELD. GRANTYIELD implies that the owner of the resource is willing to participate in a sharing of a resource that is arbitrated by a Resource Manager.

Note: GRANTYIELD protocol is not currently in version 1.1 of RESOURCE.SYS.