NXP Semiconductors PXN2020, Reference Manual, Page: 563 / 1376

Enhanced Direct Memory Access Controller (eDMA)
PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor 24-43
24.5.6 TCD Status
24.5.6.1 Minor Loop Complete
There are two methods to test for minor loop completion when using software initiated service requests.
The first method is to read the TCD.CITER field and test for a change. Another method may be extracted
from the sequence below. The second method is to test the TCD.START bit AND the TCD.ACTIVE bit.
The minor loop complete condition is indicated by both bits reading zero after the TCD.START was
written to a 1. Polling the TCD.ACTIVE bit may be inconclusive because the active status may be missed
if the channel execution is short in duration.
The TCD status bits execute the following sequence for a software activated channel:
1. TCD.START = 1, TCD.ACTIVE = 0, TCD.DONE = 0 (channel service request via software).
2. TCD.START = 0, TCD.ACTIVE = 1, TCD.DONE = 0 (channel is executing).
3. TCD.START = 0, TCD.ACTIVE = 0, TCD.DONE = 0 (channel has completed the minor loop and
is idle), or
4. TCD.START = 0, TCD.ACTIVE = 0, TCD.DONE = 1 (channel has completed the major loop and
is idle).
The best method to test for minor loop completion when using hardware initiated service requests is to
read the TCD.CITER field and test for a change. The hardware request and acknowledge handshakes
signals are not visible in the programmer’s model.
The TCD status bits execute the following sequence for a hardware activated channel:
1. eDMA peripheral request asserts (channel service request via hardware).
2. TCD.START = 0, TCD.ACTIVE = 1, TCD.DONE = 0 (channel is executing).
3. TCD.START = 0, TCD.ACTIVE = 0, TCD.DONE = 0 (channel has completed the minor loop and
is idle), or
4. TCD.START = 0, TCD.ACTIVE = 0, TCD.DONE = 1 (channel has completed the major loop and
is idle).
For both activation types, the major loop complete status is explicitly indicated via the TCD.DONE bit.
Table 24-23. Modulo Feature Example
Transfer
Number
Address
1 0x12345670
2 0x12345674
3 0x12345678
4 0x1234567C
5 0x12345670
6 0x12345674