16 KBytes data transfer
Event 25 (CPU writes 1 to ESR.E25)
ACNT = 16384
BCNT = 1
CCNT = 1
1D transfer of 16 KByte elements
OPT.ITCINTEN = 0
OPT.TCC = Don’t care
EDMA3 channel 25 setup
1K
1K
1K
1K
1K
1K
1K
1K
1K
1K
1K
1K
1K
1K
1K
Event 25 (CPU writes 1 to ESR.E25)
ITCCHEN=1, TCC=25 causes
channel 25 to be synchronized again
Time gaps allow other transfers on the same priority level
to be performed
ACNT = 1024
BCNT = 16
CCNT = 1
OPT.SYNCDIM = A SYNC
OPT.ITCCHEN = 1
OPT.TCINTEN = 1
EDMA channel 25 setup
OPT.TCC = 25
Peripheral Servicing Example
www.ti.com
Figure 3-19. Single Large Block Transfer Example
The intermediate transfer chaining enable (ITCCHEN) provides a method to break up a large transfer into
smaller transfers. For example, to move a single large block of memory (16K bytes), the EDMA3 performs
an A-synchronized transfer. The element count is set to a reasonable value, where reasonable derives
from the amount of time it would take to move this smaller amount of data. Assume 1 Kbyte is a
reasonable small transfer in this example. The EDMA3 is set up to transfer 16 arrays of 1 Kbyte elements,
for a total of 16K byte elements. The TCC field in the channel options parameter (OPT) is set to the same
value as the channel number and ITCCHEN are set. In this example, DMA channel 25 is used and TCC is
also set to 25. The TCINTEN may also be set to trigger interrupt 25 when the last 1 Kbyte array is
transferred. The CPU starts the EDMA3 transfer by writing to the appropriate bit of the event set register
(ESR.E25). The EDMA3 transfers the first 1 Kbyte array. Upon completion of the first array, intermediate
transfer complete code chaining generates a synchronization event to channel 25, a value specified by the
TCC field. This intermediate transfer completion chaining event causes DMA channel 25 to transfer the
next 1 Kbyte array. This process continues until the transfer parameters are exhausted, at which point the
EDMA3 has completed the 16K byte transfer. This method breaks up a large transfer into smaller packets,
thus providing natural time slices in the transfer such that other events may be processed.
shows the EDMA3 setup and illustration of the broken up smaller packet transfers.
Figure 3-20. Smaller Packet Data Transfers Example
84
EDMA3 Transfer Examples
SPRUG34 – November 2008
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