Enhanced Direct Memory Access (eDMA) RM0046
420/936 Doc ID 16912 Rev 5
The eDMA goes idle or services the next channel.
9. Second hardware (eDMA peripheral request) requests channel service.
10. The channel is selected by arbitration for servicing.
11. eDMA engine writes: TCD.DONE = 0, TCD.START = 0, TCD.ACTIVE = 1.
12. eDMA engine reads: channel TCD data from local memory to internal register file.
13. The source to destination transfers execute as follows:
a) read_byte (0x1010), read_byte (0x1011), read_byte (0x1012), read_byte (0x1013)
b) write_word (0x2010) first iteration of the minor loop
c) read_byte (0x1014), read_byte (0x1015), read_byte (0x1016), read_byte (0x1017)
d) write_word (0x2014) second iteration of the minor loop
e) read_byte (0x1018), read_byte (0x1019), read_byte (0x101a), read_byte (0x101b)
f) write_word (0x2018) third iteration of the minor loop
g) read_byte (0x101c), read_byte (0x101d), read_byte (0x101e), read_byte (0x101f)
h) write_word (0x201c) last iteration of the minor loop major loop complete
14. eDMA engine writes: TCD.SADDR = 0x1000, TCD.DADDR = 0x2000,
TCD.CITER = 2 (TCD.BITER).
15. eDMA engine writes: TCD.ACTIVE = 0, TCD.DONE = 1, EDMA_IRQRn =1.
16. The channel retires major loop complete.
The eDMA goes idle or services the next channel.
Modulo feature
The modulo feature of the eDMA provides the ability to easily implement a circular data
queue in which the size of the queue is a power of 2. MOD is a 5-bit field for the source and
destination in the TCD, and specifies which lower address bits are incremented from their
original value after the address + offset calculation. All upper address bits remain the same
as in the original value. Clearing this field to 0 disables the modulo feature.
Table 198 shows how the transfer addresses are specified based on the setting of the MOD
field. Here a circular buffer is created where the address wraps to the original value while
the 28 upper address bits (0x1234567x) retain their original value. In this example the
source address is set to 0x12345670, the offset is set to 4 bytes and the mod field is set to
4, allowing for a 2
4
byte (16-byte) size queue.
Table 198. Modulo feature example
Transfer Number Address
1 0x12345670
2 0x12345674
3 0x12345678
4 0x1234567C
5 0x12345670
6 0x12345674
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