PXN20RM Datasheet, PDF (560/1376 Pages) Freescale Semiconductor, Inc – PXN20 Microcontroller

Enhanced Direct Memory Access Controller (eDMA)
24.5.5 DMA Transfer
24.5.5.1 Single Request
To perform a simple transfer of n bytes of data with one activation, set the major loop to 1
(TCD.CITER = TCD.BITER = 1). The data transfer begins after the channel service request is
acknowledged and the channel is selected to execute. After the transfer is complete, the TCD.DONE bit is
set and an interrupt is generated if properly enabled.
For example, the following TCD entry is configured to transfer 16 bytes of data. The eDMA is
programmed for one iteration of the major loop transferring 16 bytes per iteration. The source memory has
a byte wide memory port located at 0x1000. The destination memory has a word wide port located at
0x2000. The address offsets are programmed in increments to match the size of the transfer; one byte for
the source and four bytes for the destination. The final source and destination addresses are adjusted to
return to their beginning values.
TCD.CITER = TCD.BITER = 1
TCD.NBYTES = 16
TCD.SADDR = 0x1000
TCD.SOFF = 1
TCD.SSIZE = 0
TCD.SLAST = –16
TCD.DADDR = 0x2000
TCD.DOFF = 4
TCD.DSIZE = 2
TCD.DLAST_SGA= -16
TCD.INT_MAJ = 1
TCD.START = 1 (Must be written last after all other fields have been initialized)
All other TCD fields = 0
This would generate the following sequence of events:
1. Slave write to the TCD.START bit requests channel service.
2. The channel is selected by arbitration for servicing.
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
24-40
PXN20 Microcontroller Reference Manual, Rev. 1
Freescale Semiconductor