ARM Technical Support Knowledge Articles

Section 2.3. Burst Size - Source and Destination

Applies to: PL08x DMAC (DM & SM)

Answer

Burst Size - Source and Destination

Do SBSize and DBSize bits in the DMACCx control register specify burst sizes in terms of source and destination widths respectively?

Yes, the SBSize does refer to the source and the DBSize to the destination burst sizes. These burst sizes indicate the number of TRANSFERS that make up a source/destination burst transfer request. This value must be set to the size of the burst size of the source/destination peripheral.

NOTE:
The burst size is the amount of data that is transferred when the DMACxBREQ signal goes active in the source/destination peripheral and is NOT related to the AHB HBURST signal (as this is often a source of confusion).

Difference in Memory and Peripheral Data Width

Assume we have a 32-bit memory and an 8-bit peripheral to transfer 7 bytes. Is it necessary to program SBSize (memory source) to 8 bits to match DBSize (peripheral destination)?

The amount of data to be transferred must be divisible by the source and destination transferwidths. To transfer 7 bytes of data both the source and destination must be byte-wide.

Article last edited on: 2008-09-09 15:47:25

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