Enhanced Direct Memory Access (eDMA)
MCF52277 Reference Manual, Rev. 1
Freescale Semiconductor
17-37
loop is exhausted, only the major loop channel link fields are used to determine if a channel link should be
made. For example, the initial fields of:
TCD
n
_CITER[E_LINK] = 1
TCD
n
_CITER[LINKCH] = 0xC
TCD
n
_CITER[CITER] value = 0x4
TCD
n
_CSR[MAJOR_E_LINK] = 1
TCD
n
_CSR[MAJOR_LINKCH] = 0x7
executes as:
1. Minor loop done
→
set TCD12_CSR[START] bit
2. Minor loop done
→
set TCD12_CSR[START] bit
3. Minor loop done
→
set TCD12_CSR[START] bit
4. Minor loop done, major loop done
→
set TCD7_CSR[START] bit
When minor loop linking is enabled (TCD
n
_CITER[E_LINK] = 1), the TCD
n
_CITER[CITER] field uses
a nine bit vector to form the current iteration count. When minor loop linking is disabled
(TCD
n
_CITER[E_LINK] = 0), the TCD
n
_CITER[CITER] field uses a 15-bit vector to form the current
iteration count. The bits associated with the TCD
n
_CITER[LINKCH] field are concatenated onto the
CITER value to increase the range of the CITER.
NOTE
The TCD
n
_CITER[E_LINK] bit and the TCD
n
_BITER[E_LINK] bit must
equal or a configuration error is reported. The CITER and BITER vector
widths must be equal to calculate the major loop, half-way done interrupt
point.
summarizes how a DMA channel can link to another DMA channel, i.e, use another channel’s
TCD, at the end of a loop.
17.8.7
Dynamic Programming
This section provides recommended methods to change the programming model during channel execution.
17.8.7.1
Dynamic Channel Linking and Dynamic Scatter/Gather
Dynamic channel linking and dynamic scatter/gather is the process of changing the
TCD
n
_CSR[MAJOR_E_LINK] or TCD
n
_CSR[E_SG] bits during channel execution. These bits are read
Table 17-35. Channel Linking Parameters
Desired Link
Behavior
TCD Control Field Name
Description
Link at end of
Minor Loop
CITER[E_LINK]
Enable channel-to-channel linking on minor loop completion (current iteration)
CITER[LINKCH]
Link channel number when linking at end of minor loop (current iteration)
Link at end of
Major Loop
CSR[MAJOR_E_LINK]
Enable channel-to-channel linking on major loop completion
CSR[MAJOR_LINKCH]
Link channel number when linking at end of major loop
Содержание MCF52277
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