Information

The following figure shows how each DMA request initiates one minor-loop transfer, or
iteration, without CPU intervention. DMA arbitration can occur after each minor loop,
and one level of minor loop DMA preemption is allowed. The number of minor loops in
a major loop is specified by the beginning iteration count (BITER).
DMA request
DMA request
DMA request
Minor loopMinor loopMinor loop
Major loop
Current major
loop iteration
count (CITER)
3
2
1
Source or destination memory
Figure 21-292. Example of multiple loop iterations
The following figure lists the memory array terms and how the TCD settings interrelate.
xADDR: (Starting address)
xLAST: Number of bytes added to
current address after major loop
(typically used to loop back)
Minor loop
(NBYTES in
minor loop,
often the same
value as xSIZE)
Minor loop
Last minor loop
Offset (xOFF): number of bytes added to
current address after each transfer
(often the same value as xSIZE)
Each DMA source (S) and
destination (D) has its own:
Address (xADDR)
Size (xSIZE)
Offset (xOFF)
Modulo (xMOD)
Last Address Adjustment (xLAST)
where x = S or D
Peripheral queues typically
have size and offset equal
to NBYTES.
xSIZE: (size of one
data transfer)
Figure 21-293. Memory array terms
Chapter 21 Direct Memory Access Controller (eDMA)
K10 Sub-Family Reference Manual, Rev. 6, Nov 2011
Freescale Semiconductor, Inc. 479