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HOW DMA IS INITIATED AND HOW DMA CONTROLLER WORKS?
Sunidhi
on 2011-09-30 09:30:00Transfers are initiated when the DMA controller is notified of the need to move data to the memory by some event (keyboard press or mouse click, for examples). The controller asserts a DMA request signal to the CPU to use the system bus. The CPU completes its current operation and yields control of the bus to the DMA controller via a DMA acknowledge signal. The controller then reads and writes data and controls signals as if it is the CPU, which at that instant is tri-stated (idled). Upon completion of the transfer, DMA controller de-asserts the DMA request signal and the CPU in turn removes its DMA acknowledge signal and resumes control of the bus.
Sunidhi
on 2011-09-30 09:30:00Implementations Synchronous DMA moves a byte or word at a time between system memory and a peripheral. After completing each transfer, the DMA asks the I/O port to signal when the latter is ready for another transaction. In this set-up, the DMA and the CPU shares the bus cycles, with the DMA winning any contest for system bus control. Burst Mode DMA assumes that both the destination and source can take transfers as quickly as the controller can make them. The CPU sets up the controller, and after a signal from the I/O port, the entire data is copied to the destination. The DMA controller has sole access to the system bus during the transfer which is very rapid compared to synchronous DMA. Flyby DMA, which is not supported by all controllers, puts out the source or destination address, then initiates a simultaneous read and write cycle. Flyby transfers are very fast as the read cycle and write cycle are compressed to a single cycle. Flyby can support both burst and synchronous types of transactions.
ALOK
on 2011-10-02 09:30:00just read the book and follow it... u r wasting ur time by asking silly theory questions