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Enhanced Direct Memory Access (eDMA)
Freescale Semiconductor
19-29
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 read the entire TCD, including the TCD
control and status fields (
) 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 the source address, TCD
n
_SADDR) to the destination (as defined
by the destination address, TCD
n
_DADDR) continue until the specified number of bytes
(TCD
n
_NBYTES) are transferred. When transfer is complete, the eDMA engine's local TCD
n
_SADDR,
TCD
n
_DADDR, and TCD
n
_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
(interrupts, major loop channel linking, and scatter/gather operations) if enabled.
shows how each DMA request initiates one minor-loop transfer (iteration) without CPU
intervention. DMA arbitration can occur after each minor loop, and one level of minor loop DMA
preemption is allowed. The number of minor loops in a major loop is specified by the beginning iteration
count (BITER).
Table 19-31. TCD Control and Status Fields
TCD
n
_CSR
Field Name
Description
START
Control bit to start channel explicitly when using a software
initiated DMA service (Automatically cleared by hardware)
ACTIVE
Status bit indicating the channel is currently in execution
DONE
Status bit indicating major loop completion (cleared by software
when using a software initiated DMA service)
D_REQ
Control bit to disable DMA request at end of major loop
completion when using a hardware initiated DMA service
BWC
Control bits for throttling bandwidth control of a channel
E_SG
Control bit to enable scatter-gather feature
INT_HALF
Control bit to enable interrupt when major loop is half complete
INT_MAJ
Control bit to enable interrupt when major loop completes
Summary of Contents for MCF54455
Page 33: ...xxviii Freescale Semiconductor ...
Page 67: ...Freescale Semiconductor 1 ...
Page 125: ...Freescale Semiconductor 1 ...
Page 145: ...Enhanced Multiply Accumulate Unit EMAC 5 21 Freescale Semiconductor ...
Page 173: ...Cache 6 28 Freescale Semiconductor ...
Page 179: ...Static RAM SRAM 7 6 Freescale Semiconductor ...
Page 207: ...Power Management 9 16 Freescale Semiconductor ...
Page 323: ...Reset Controller Module 13 8 Freescale Semiconductor ...
Page 389: ...Pin Multiplexing and Control 16 44 Freescale Semiconductor ...
Page 575: ...PCI Bus Controller 22 58 Freescale Semiconductor ...
Page 600: ...Advanced Technology Attachment ATA Freescale Semiconductor 23 25 ...
Page 601: ...Freescale Semiconductor 1 ...
Page 842: ...I2 C Interface Freescale Semiconductor 33 16 ...
Page 843: ...Freescale Semiconductor 1 ...
Page 921: ...Revision History A 6 Freescale Semiconductor ...