1. Switch to Round-Robin Channel Arbitration mode, change the channel priorities,
then switch back to Fixed Arbitration mode,
2. Disable all the channels, change the channel priorities, then enable the appropriate
channels.
22.5.7.2 Dynamic channel linking
Dynamic channel linking is the process of setting the TCD.major.e_link bit during
channel execution (see the diagram in TCD structure). This bit is read from the TCD
local memory at the end of channel execution, thus allowing the user to enable the feature
during channel execution.
Because the user is allowed to change the configuration during execution, a coherency
model is needed. Consider the 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.
The following coherency model is recommended when executing a dynamic channel link
request.
1. Write 1 to the TCD.major.e_link bit.
2. Read back the TCD.major.e_link bit.
3. Test the TCD.major.e_link request status:
• If TCD.major.e_link = 1, the dynamic link attempt was successful.
• If TCD.major.e_link = 0, the attempted dynamic link did not succeed (the
channel was already retiring).
For this request, the TCD local memory controller forces the TCD.major.e_link bit to
zero on any writes to a channel’s TCD.word7 after that channel’s TCD.done bit is set,
indicating the major loop is complete.
NOTE
The user must clear the TCD.done bit before writing the
TCD.major.e_link bit. The TCD.done bit is cleared
automatically by the eDMA engine after a channel begins
execution.
Initialization/application information
K22F Sub-Family Reference Manual, Rev. 4, 08/2016
504 NXP Semiconductors
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