Method and apparatus for the context switching of devices

Details Method and apparatus for the context switching of devices Method and apparatus for the context switching of devices

1989-09-28

1992-06-30

Heckler, Thomas M.

Boots, shoes, and leggings

364DIG1, 3642817, 3642463, 3642543, 3642613, G06F 946

Patent

active

051270986

ABSTRACT:
The system of the present invention provides for the context switching of devices connected through the system's memory management unit and is particularly useful in a multi-tasking computer system in which multiple processes access the same device. In the method and apparatus of the present invention, devices that are connected to the system through the MMU are controlled using the page fault mechanism of the MMU and the page fault handler in each segment. Addresses are allocated in the process address space for each process to provide for the addressing of the devices and device queues connected through the MMU, such that one device or one device queue is mapped into one segment of each process address space that will access the device. The "valid bits" associated with each page in a segment are turned on/off by the process or operating system in order to control the device. If the valid bits are off and an attempt is made to access at the address a page fault occurs and the page fault mechanism invokes the page fault handler of the corresponding segment. The page fault mechanism of the MMU and the page fault handler of each segment are then utilized to perform a context switch of the device.

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Voorhies et al., "Virtual Graphics", Computer Graphics, vol. 22, No. 4 (Aug. 1988).

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