Datasheet

• When XDMAC_CC.INITD is set to 0, XDMAC_CUBC.UBLEN and XDMAC_CNDA.NDA field values are

unreliable when the descriptor is being updated. The following procedure applies to get the buf

fer descriptor

identifier and the residual bytes:

Read XDMAC_CNDAx.NDA(nda0)

Read XDMAC_CCx.INITD(initd0)

Read XDMAC_CUBCx.UBLEN(ublen)

Read XDMAC_CCx.INITD(initd1)

Read XDMA_CNDAx.NDA(nda1)

If (nda0 == nda1 && initd0 == 1 && initd1 == 1).

Then the ublen is correct, the buffer id is nda.

Else retry

See the figure below

Figure 36-4. INITD Timing Diagram

buffer0 buffer1 buffer0 buffer1 buffer0

XDMAC_CUBCx.UBLEN

XDMAC_CCx.INITD

XDMAC_CUBCx.UBLEN

XDMAC_CNDAx.NDA

0 buffer1.ublen buffer0.ublen

buffer1.nda buffer0.nda

r1.

SAM E70/S70/V70/V71 Family

DMA Controller (XDMAC)

echnology Inc.

Datasheet

DS60001527D-page 465