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Enhanced Direct Memory Access (eDMA)
Freescale Semiconductor
19-17
19.4.16 Transfer Control Descriptors (TCD
n
)
Each channel requires a 32-byte transfer control descriptor for defining the desired data movement
operation. The channel descriptors are stored in the local memory in sequential order: channel 0, channel
1,... channel 15. Each TCD
n
definition is presented as 11 registers of 16 or 32 bits.
is a register
list of the basic TCD structure.
The following figures and tables define the fields of the TCD
n
structure:
Table 19-18. DCHPRI
n
Field Descriptions
Field
Description
7
ECP
Enable channel preemption.
0 Channel
n
cannot be suspended by a higher priority channel’s service request.
1 Channel
n
can be temporarily suspended by the service request of a higher priority channel.
6–4
Reserved, must be cleared.
3–0
CHPRI
Channel
n
arbitration priority. Channel priority when fixed-priority arbitration is enabled.
Table 19-19. TCD
n
Memory Structure
eDMA Offset
TCD
n
Register Name
Abbreviation
Width
(bits)
0xFC0 (0x20
n
)
Source Address
TCD
n
_SADDR
32
0xFC0 (0x20
n
)
Transfer Attributes
TCD
n
_ATTR
16
0xFC0 (0x20
n
)
Signed Source Address Offset
TCD
n
_SOFF
16
0xFC0 (0x20
n
)
Minor Byte Count
TCD
n
_NBYTES
32
0xFC0 (0x20
n
)
Last Source Address Adjustment
TCD
n
_SLAST
32
0xFC0 (0x20
n
)
Destination Address
TCD
n
_DADDR
32
0xFC0 (0x20
n
)
Current Minor Loop Link, Major Loop Count
TCD
n
_CITER
16
0xFC0 (0x20
n
)
Signed Destination Address Offset
TCD
n
_DOFF
16
0xFC0 (0x20
n
)
Last Destination Address Adjustment/Scatter Gather Address TCD
n
_DLAST_SGA
32
0xFC0 (0x20
n
)
Beginning Minor Loop Link, Major Loop Count
TCD
n
_BITER
16
0xFC0 (0x20
n
)
Control and Status
TCD
n
_CSR
16
Address: 0xFC0 (0x20
n
) (TCD
n
_SADDR)
Access: User read/write
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10
9
8
7
6
5
4
3
2
1
0
R
SADDR
W
Reset – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –
Figure 19-18. TCD
n
Source Address (TCD
n
_SADDR)
Содержание MCF54455
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