NXP Semiconductors MPC5644A, Reference Manual, Page: 191 / 1735

Enhanced Direct Memory Access Controller (eDMA)
MPC5644A Microcontroller Reference Manual, Rev. 6
Freescale Semiconductor 191
8.5.8.2.2 Method 2 (channel using major loop linking)
For a channel using major loop channel linking, the coherency model in Table 8-27 may be used for a
dynamic scatter/gather request. This method uses the TCD.dlast_sga field as a TCD indentification (ID).
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).
Table 8-27. Coherency model for method 2
Step Action
1 Write 1b to theTCD.d_req bit.
Note: 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).
Table 8-26. Coherency model for method 1 (continued)
Step Action