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Enhanced Direct Memory Access (eDMA)
MPC5566 Microcontroller Reference Manual, Rev. 2
Freescale Semiconductor
9-47
3. eDMA engine writes: TCD.DONE = 0, TCD.START = 0, TCD.ACTIVE = 1.
4. eDMA engine reads: channel TCD data from local memory to internal register file.
5. The source to destination transfers are executed as follows:
a) read_byte (0x1000), read_byte(0x1001), read_byte(0x1002), read_byte(0x1003)
b) write_word (0x2000) -> first iteration of the minor loop
c) read_byte (0x1004), read_byte(0x1005), read_byte(0x1006), read_byte(0x1007)
d) write_word (0x2004) -> second iteration of the minor loop
e) read_byte (0x1008), read_byte(0x1009), read_byte(0x100a), read_byte(0x100b)
f) write_word (0x2008) -> third iteration of the minor loop
g) read_byte (0x100c), read_byte(0x100d), read_byte(0x100e), read_byte(0x100f)
h) write_word (0x200c) -> last iteration of the minor loop -> major loop complete
6. eDMA engine writes: TCD.SADDR = 0x1000, TCD.DADDR = 0x2000,
TCD.CITER = 1 (TCD.BITER).
7. eDMA engine writes: TCD.ACTIVE = 0, TCD.DONE = 1, EDMA_IRQR
n
= 1.
8. The channel retires.
The eDMA goes idle or services the next channel.
9.4.5.2
Multiple Requests
The next example is the same as previous with the exception of transferring 32 bytes via two hardware
requests. The only fields that change are the major loop iteration count and the final address offsets. The
eDMA is programmed for two iterations of the major loop transferring 16 bytes per iteration. After the
channel’s hardware requests are enabled in the EDMA_ERQR, channel service requests are initiated by
the slave device (set ERQR after TCD; TCD.START = 0).
TCD.CITER = TCD.BITER = 2
TCD.NBYTES = 16
TCD.SADDR = 0x1000
TCD.SOFF = 1
TCD.SSIZE = 0
TCD.SLAST = –32
TCD.DADDR = 0x2000
TCD.DOFF = 4
TCD.DSIZE = 2
TCD.DLAST_SGA= –32
TCD.INT_MAJ = 1
TCD.START = 0 (Initialize all other fields before writing this bit.)
All other TCD fields = 0
Содержание MPC5566
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