
Enhanced Direct Memory Access (eDMA)
MCF52277 Reference Manual, Rev. 1
17-2
Freescale Semiconductor
17.3
Features
The eDMA is a highly-programmable data-transfer engine optimized to minimize the required
intervention from the host processor. It is intended for use in applications where the data size to be
transferred is statically known and not defined within the data packet itself. The eDMA module features:
•
All data movement via dual-address transfers: read from source, write to destination
— Programmable source and destination addresses and transfer size, plus support for enhanced
addressing modes
•
16-channel implementation that performs complex data transfers with minimal intervention from
a host processor
— Internal data buffer, used as temporary storage to support 16-byte burst transfers
— Connections to the crossbar switch for bus mastering the data movement
•
Transfer control descriptor (TCD) organized to support two-deep, nested transfer operations
— 32-byte TCD stored in local memory for each channel
— An inner data transfer loop defined by a minor byte transfer count
— An outer data transfer loop defined by a major iteration count
•
Channel activation via one of three methods:
— Explicit software initiation
— Initiation via a channel-to-channel linking mechanism for continual transfers
— Peripheral-paced hardware requests (one per channel)
•
Support for fixed-priority and round-robin channel arbitration
•
Channel completion reported via optional interrupt requests
— One interrupt per channel, optionally asserted at completion of major iteration count
— Error terminations are optionally enabled per channel and logically summed together to form
one error interrupt to the interrupt controller
•
Optional support for scatter/gather DMA processing
Throughout this chapter,
n
is used to reference the channel number.
17.4
Modes of Operation
17.4.1
Normal Mode
In normal mode, the eDMA transfers data between a source and a destination. The source and destination
can be a memory block or an I/O block capable of operation with the eDMA.
A service request initiates a transfer of a specific number of bytes (NBYTES) as specified in the transfer
control descriptor (TCD). The minor loop is the sequence of read-write operations that transfers these
NBYTES per service request. A major loop is the number of minor loop iterations defining a task.
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