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).
22.5.7.3.2 Method 2 (channel using major loop channel linking)
For a channel using major loop channel linking, the coherency model described here may
be used for a dynamic scatter/gather request. This method uses the TCD.dlast_sga field as
a TCD indentification (ID).
1. Write 1b to the TCD.d_req bit.
Should a dynamic scatter/gather attempt fail, setting the 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.
2. Write theTCD.dlast_sga field with the scatter/gather address.
3. Write 1b to the TCD.e_sg bit.
4. Read back the TCD.e_sg bit.
5. Test the TCD.e_sg request status:
If e_sg = 1b, the dynamic link attempt was successful.
If e_sg = 0b, read the 32 bit TCD dlast_sga field.
If e_sg = 0b and the dlast_sga did not change, the attempted dynamic link did not
succeed (the channel was already retiring).
If e_sg = 0b and the dlast_sga changed, the dynamic link attempt was successful (the
new TCD’s e_sg value cleared the e_sg bit).
Chapter 22 Enhanced Direct Memory Access (eDMA)
K22F Sub-Family Reference Manual , Rev. 3, 7/2014
Freescale Semiconductor, Inc.
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