PXN20RM Datasheet, PDF (561/1376 Pages) Freescale Semiconductor, Inc – PXN20 Microcontroller

Enhanced Direct Memory Access Controller (eDMA)
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_IRQRn = 1.
8. The channel retires.
The eDMA goes idle or services the next channel.
24.5.5.2 Multiple Requests
The next example is the same as previous, excepting 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 (ERQR should be set after TCD). Note that 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 (Must be written last after all other fields have been initialized)
All other TCD fields = 0
This generates the following sequence of events:
1. First hardware (eDMA peripheral request) request for 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
Freescale Semiconductor
PXN20 Microcontroller Reference Manual, Rev. 1
24-41