NXP Semiconductors PXN2020, Reference Manual, Page: 565 / 1376

Enhanced Direct Memory Access Controller (eDMA)
PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor 24-45
3. Minor loop done

set channel 12 TCD.START bit
4. Minor loop done, major loop done

set channel 7 TCD.START bit
When minor loop linking is enabled (TCD.CITER.E_LINK = 1), the TCD.CITER field uses a nine bit
vector to form the current iteration count.
When minor loop linking is disabled (TCD.CITER.E_LINK = 0), the TCD.CITER field uses a 15-bit
vector to form the current iteration count. The bits associated with the TCD.CITER.LINKCH field are
concatenated onto the CITER value to increase the range of the CITER.
NOTE
After configuration, the TCD.CITER.E_LINK bit and the
TCD.BITER.E_LINK bit must be equal or a configuration error is reported.
The CITER and BITER vector widths must be equal to calculate the major
loop, halfway done interrupt point.
Table 24-24 summarizes how a DMA channel can link to another DMA channel, i.e, use another channel’s
TCD, at the end of a loop.
24.5.8 Dynamic Programming
This section provides recommended methods to change the programming model during channel execution.
24.5.8.1 Dynamic Channel Linking and Dynamic Scatter-Gather Operation
Dynamic channel linking and dynamic scatter-gather operation is the process of changing the
TCD.MAJOR.E_LINK or TCD.E_SG bits during channel execution. These bits are read from the TCD
local memory at the end of channel execution thus allowing the user to enable either feature during channel
execution.
Because the user is allowed to change the configuration during execution, a coherency model is needed.
Consider a scenario where the user attempts to execute a dynamic channel link by enabling the
TCD.MAJOR.E_LINK bit at the same time the eDMA engine is retiring the channel. The
TCD.MAJOR.E_LINK would be set in the programmer’s model, but it would be unclear whether the
actual link was made before the channel retired.
Table 24-24. Channel Linking Parameters
Desired Link
Behavior
TCD Control Field Name Description
Link at end of
minor loop
citer.e_link Enable channel-to-channel linking on minor loop
completion (current iteration).
citer.linkch Link channel number when linking at end of minor
loop (current iteration).
Link at end of
major loop
major.e_link Enable channel-to-channel linking on major loop
completion.
major.linkch Link channel number when linking at end of major
loop.