NXP Semiconductors Kinetis KE1xZ256, Reference Manual

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13.5.4.3 Using the modulo feature
The modulo feature of the eDMA provides the ability to implement a circular data queue
in which the size of the queue is a power of 2. MOD is a 5-bit field for the source and
destination in the TCD, and it specifies which lower address bits increment from their
original value after the offset calculation. All upper address bits remain the same
as in the original value. A setting of 0 for this field disables the modulo feature.
The following table shows how the transfer addresses are specified based on the setting
of the MOD field. Here a circular buffer is created where the address wraps to the
original value while the 28 upper address bits (0x1234567x) retain their original value. In
this example the source address is set to 0x12345670, the offset is set to 4 bytes and the
MOD field is set to 4, allowing for a 2
4
byte (16-byte) size queue.
Table 13-9. Modulo example
Transfer Number Address
1 0x12345670
2 0x12345674
3 0x12345678
4 0x1234567C
5 0x12345670
6 0x12345674
13.5.5 Monitoring transfer descriptor status
This section discusses how to monitor eDMA status.
13.5.5.1 Testing for minor loop completion
There are two methods to test for minor loop completion when using software initiated
service requests. The first is to read the TCDn_CITER field and test for a change.
Another method may be extracted from the sequence shown below. The second method is
to test the TCDn_CSR[START] bit and the TCDn_CSR[ACTIVE] bit. The minor-loop-
complete condition is indicated by both bits reading zero after the TCDn_CSR[START]
was set. Polling the TCDn_CSR[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:
Initialization/application information
Kinetis KE1xZ256 Sub-Family Reference Manual, Rev. 3, 07/2018
258 NXP Semiconductors