1. User write to the TCDn_CSR[START] bit requests channel service.
2. The channel is selected by arbitration for servicing.
3. eDMA engine writes: TCDn_CSR[DONE] = 0, TCDn_CSR[START] = 0,
TCDn_CSR[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 from location 0x1000, read byte from location 0x1001, read byte from
0x1002, read byte from 0x1003.
b. Write 32-bits to location 0x2000
→
first iteration of the minor loop.
c. Read byte from location 0x1004, read byte from location 0x1005, read byte from
0x1006, read byte from 0x1007.
d. Write 32-bits to location 0x2004
→
second iteration of the minor loop.
e. Read byte from location 0x1008, read byte from location 0x1009, read byte from
0x100A, read byte from 0x100B.
f. Write 32-bits to location 0x2008
→
third iteration of the minor loop.
g. Read byte from location 0x100C, read byte from location 0x100D, read byte
from 0x100E, read byte from 0x100F.
h. Write 32-bits to location 0x200C
→
last iteration of the minor loop
→
major loop
complete.
6. The eDMA engine writes: TCDn_SADDR = 0x1000, TCDn_DADDR = 0x2000,
TCDn_CITER = 1 (TCDn_BITER).
7. The eDMA engine writes: TCDn_CSR[ACTIVE] = 0, TCDn_CSR[DONE] = 1,
INT[n] = 1.
8. The channel retires and the eDMA goes idle or services the next channel.
22.5.4.2 Multiple requests
The following example transfers 32 bytes via two hardware requests, but is otherwise the
same as the previous example. 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 ERQ register, the slave device initiates channel service requests.
Initialization/application information
K22F Sub-Family Reference Manual , Rev. 3, 7/2014
490
Freescale Semiconductor, Inc.
