ARM Technical Support Knowledge Articles

Section 2.11. DMAC Channels

Applies to: PL08x DMAC (DM & SM)

Answer

The DMAC mentions 8 DMA channels. There are 16 request lines (16 for single and 16 for burst requests). It does not mention anything about requests and channel mapping. Is there a link between these two?

Request lines and channels are unrelated.

A channel can be programmed to use any of the 16 requests as a source request (if necessary), and any of the 16 requests as a destination request (if necessary). The Technical Reference Manual shows 4 bits and this is what should be referred to.

The DMAC documentation mentions that the SrcPeripheral and DestPeripheral bits in the DMACCx configuration register, whereas the RTL shows them as 5 bits rather than 4. Why is there a discrepancy?

The RTL code shows 5 bits and this has been done to allow for future expansion. You should follow what is in the Technical Reference Manual as bit 5 of the configuration register is reserved and must be written zero.

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

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