Analog Devices ADSP-2106x SHARC User Manual page 232

6 DMA
Second cycle:
• The X Count is restored into the C register from the DA register.
• The Y Increment value in the DB register is added to the current
address in II.
• The Y Count in GP is decremented.
• If the Y Count is zero, the DMA sequence is ended and the channel
becomes inactive until the Next Pointer is written again.
A key point about the 2-D DMA sequence (or any DMA sequence) is
that the first DMA transfer begins before the address is modified. This
means that DMA cannot be disabled by setting either the X Count or
the Y Count to zero. To do one-dimensional DMA transfers in 2-D
mode, the Y Count must be initialized to one.
When the X Count becomes zero but the Y Count is non-zero, the
X Count must be reloaded with the original value. The C register
functions as the working count register. The DA register holds the
original count value. C is loaded from DA to restore the count. The DA
register is written automatically whenever the C register is written.
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