Information

21.5.7.2 Dynamic channel linking
Dynamic channel linking is the process of setting the TCD.major.e_link bit during
channel execution. 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.
Step Action
1 Write 1b 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 = 1b, the dynamic link attempt was
successful.
• If TCD.major.e_link = 0b, 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.
21.5.7.3 Dynamic scatter/gather
Dynamic scatter/gather is the process of setting the TCD.e_sg bit during channel
execution. 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
scatter/gather operation by enabling the TCD.e_sg bit at the same time the eDMA engine
Initialization/application information
K20 Sub-Family Reference Manual, Rev. 2, Feb 2012
394 Freescale Semiconductor, Inc.