Direct memory access is used f

[问答题]

Direct memory access is used for high-speed I/O devices in order to avoid increasing the CPU´s execution load.

a.How does the CPU interface with the device to coordinate the transfer?

b.How does the CPU know when the memory operations are complete?

c.The CPU is allowed to execute other programs while the DMA controller is transferring data.Does this process interfere with the execution of the user programs?If so,describe what forms of interference are caused.

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Smizy

The CPU can initiate a DMA operation by writing values into special registers that can be independently accessed by the device.The device initiates the corresponding operation once it receives a command from the CPU.When the device is ﬁnished with its operation,it interrupts the CPU to indicate the completion of the operation.

Both the device and the CPU can be accessing memory simultaneously.The memory controller provides access to the memory bus in a fair manner to these two entities.A CPU might therefore be unable to issue memory operations at peak speeds since it has to compete with the device in order to obtain access to the memory bus.

发表于 2018-05-05 21:19:57 回复(0)