Information

21.5 Initialization/application information
The following sections discuss initialization of the eDMA and programming
considerations.
21.5.1 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.
As the TCD is read, the first transfer is initiated on the internal bus, unless a
configuration error is detected. Transfers from the source, as defined by TCDn_SADDR,
to the destination, as defined by TCDn_DADDR, continue until the number of bytes
specified by TCDn_NBYTES are transferred.
When the transfer is complete, the eDMA engine's local TCDn_SADDR,
TCDn_DADDR, and TCDn_CITER are written back to the main TCD memory and any
minor loop channel linking is performed, if enabled. If the major loop is exhausted,
further post processing executes, such as interrupts, major loop channel linking, and
scatter/gather operations, if enabled.
Initialization/application information
K20 Sub-Family Reference Manual, Rev. 1.1, Dec 2012
456
Preliminary
Freescale Semiconductor, Inc.
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