NXP Semiconductors Kinetis KE1xZ256, Reference Manual

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Two cycles account for the arbitration pipeline and one extra cycle on the hardware
request resulting from the internal registering of the eDMA peripheral request signals.
For the peak request rate calculations above, the arbitration and request registering is
absorbed in or overlaps the previous executing channel.
Note
When channel linking or scatter/gather is enabled, a two cycle
delay is imposed on the next channel selection and startup. This
allows the link channel or the scatter/gather channel to be
eligible and considered in the arbitration pool for next channel
selection.
13.5 Initialization/application information
The following sections discuss initialization of the eDMA and programming
considerations.
13.5.1 eDMA initialization
To initialize the eDMA:
1. Write to the CR if a configuration other than the default is desired.
2. Write the channel priority levels to the DCHPRIn registers if a configuration other
than the default is desired.
3. Enable error interrupts in the EEI register if so desired.
4. Write the 32-byte TCD for each channel that may request service.
5. Enable any hardware service requests via the ERQ register.
6. Request channel service via either:
• Software: setting the TCDn_CSR[START]
• Hardware: slave device asserting its eDMA peripheral request signal
After any channel requests service, a channel is selected for execution based on the
arbitration and priority levels written into the programmer's model. The eDMA engine
reads the entire TCD, including the TCD control and status fields, as shown in the
following table, for the selected channel into its internal address path module.
Chapter 13 Enhanced Direct Memory Access (eDMA)
Kinetis KE1xZ256 Sub-Family Reference Manual, Rev. 3, 07/2018
NXP Semiconductors 251