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In DMA, there are two modes of transferring data: burst and cycle stealing. Also, there are two states of CPU when operating DMA: either it's blocked or consumed.

I want to know whether CPU is blocked or consumed when operating in burst mode, and same for cycle stealing mode.

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In burst transfer mode all data from device buffer to main memory is transferred by DMA and during that time CPU is in blocked state.

Similarly, In cycle stealing mode, if sufficient data(say data that can be transferred in only one cycle) is collected in device buffer, one cycle will be given to DMA for data transfer. and during that data transfer CPU is in blocked state.

Reason behind blocked state is that buses are common(or shared) between DMA and CPU.

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ankitgupta.1729 asked Jul 29, 2017
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Please Explain the formulae for % time of CPU blocked in both Cycle Stealing mode and Burst mode of DMA