Information

cleared automatically by the eDMA engine after a channel
begins execution.
21.5.7.3.1 Method 1 (channel not using major loop channel linking)
For a channel not using major loop channel linking, the coherency model described here
may be used for a dynamic scatter/gather request.
When the TCD.major.e_link bit is zero, the TCD.major.linkch field is not used by the
eDMA. In this case, the TCD.major.linkch bits may be used for other purposes. This
method uses the TCD.major.linkch field as a TCD indentification (ID).
1. When the descriptors are built, write a unique TCD ID in the TCD.major.linkch field
for each TCD associated with a channel using dynamic scatter/gather.
2. Write 1b to the TCD.d_req bit.
Should a dynamic scatter/gather attempt fail, setting the TCD.d_req bit will prevent a
future hardware activation of this channel. This stops the channel from executing
with a destination address (daddr) that was calculated using a scatter/gather address
(written in the next step) instead of a dlast final offest value.
3. Write the TCD.dlast_sga field with the scatter/gather address.
4. Write 1b to the TCD.e_sg bit.
5. Read back the 16 bit TCD control/status field.
6. Test the TCD.e_sg request status and TCD.major.linkch value:
If e_sg = 1b, the dynamic link attempt was successful.
If e_sg = 0b and the major.linkch (ID) did not change, the attempted dynamic link
did not succeed (the channel was already retiring).
If e_sg = 0b and the major.linkch (ID) changed, the dynamic link attempt was
successful (the new TCD’s e_sg value cleared the e_sg bit).
21.5.7.3.2 Method 2 (channel using major loop channel linking)
Initialization/application information
K20 Sub-Family Reference Manual, Rev. 1.1, Dec 2012
468
Preliminary
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