
471
SAM9G15 [DATASHEET]
11052E–ATARM–06-Feb-13
3.
Write the starting destination address in the DMAC_DADDRx register for channel x.
The values in the LLI.DMAC_DADDRx register location of each Linked List Item (LLI) in memory, although
fetched during an LLI fetch, are not used.
Write the channel configuration information into the DMAC_CFGx register for channel x.
1.
Designate the handshaking interface type (hardware or software) for the source and destination peripherals.
This is not required for memory. This step requires programming the SRC_H2SEL/DST_H2SEL bits,
respectively. Writing a ‘1’ activates the hardware handshaking interface to handle source/destination
requests for the specific channel. Writing a ‘0’ activates the software handshaking interface to handle
source/destination requests.
2.
If the hardware handshaking interface is activated for the source or destination peripheral, assign the hand-
shaking interface to the source and destination peripherals. This requires programming the SRC_PER and
DST_PER bits, respectively.
Make sure that all LLI.DMAC_CTRLBx register locations of the LLI (except the last) are set as shown in Row 2 of
Table 31-3 on page 456
, while the LLI.DMAC_CTRLBx register of the last Linked List item must be set as
described in Row 1 of
Table 31-3
.
Figure 31-5 on page 455
shows a Linked List example with two list items.
Make sure that the LLI.DMAC_DSCRx register locations of all LLIs in memory (except the last) are non-zero and
point to the next Linked List Item.
Make sure that the LLI.DMAC_SADDRx register locations of all LLIs in memory point to the start source buffer
address proceeding that LLI fetch.
Make sure that the LLI.DMAC_CTRLAx.DONE field of the LLI.DMAC_CTRLAx register locations of all LLIs in
memory is cleared.
If source Picture-in-Picture is enabled (DMAC_CTRLBx.SPIP is enabled), program the DMAC_SPIPx register for
channel x.
10. If destination Picture-in-Picture is enabled (DMAC_CTRLBx.DPIP is enabled), program the DMAC_DPIPx register
for channel x.
11. Clear any pending interrupts on the channel from the previous DMAC transfer by reading the interrupt status
register.
12. Program the DMAC_CTRLAx, DMAC_CTRLBx and DMAC_CFGx registers according to Row 2 as shown in
Table
31-3 on page 456
13. Program the DMAC_DSCRx register with DMAC_DSCRx(0), the pointer to the first Linked List item.
14. Finally, enable the channel by writing a ‘1’ to the DMAC_CHER.ENAx bit. The transfer is performed. Make sure
that bit 0 of the DMAC_EN register is enabled.
15. The DMAC fetches the first LLI from the location pointed to by DMAC_DSCRx(0).
Note:
The LLI.DMAC_SADDRx, LLI.DMAC_DADDRx, LLI.DMAC_DSCRx and LLI.DMAC_CTRLA/Bx registers are
fetched. The LLI.DMAC_DADDRx register location of the LLI, although fetched, is not used. The
DMAC_DADDRx register in the DMAC remains unchanged.
16. Source and destination requests single and chunk DMAC transactions to transfer the buffer of data (assuming
non-memory peripherals). The DMAC acknowledges at the completion of every transaction (chunk and single) in
the buffer and carries out the buffer transfer.
17. Once the buffer of data is transferred, the DMAC_CTRLAx register is written out to the system memory at the
same location and on the same layer (DMAC_DSCRx.DSCR_IF) where it was originally fetched, that is, the loca-
tion of the DMAC_CTRLAx register of the linked list item fetched prior to the start of the buffer transfer. Only
DMAC_CTRLAx register is written out because only the DMAC_CTRLAx.BTSIZE and DMAC_CTRLAX.DONE
fields have been updated by DMAC hardware. Additionally, the DMAC_CTRLAx.DONE bit is asserted when the
buffer transfer has completed.
Note:
Do not poll the DMAC_CTRLAx.DONE bit in the DMAC memory map. Instead, poll the
LLI.DMAC_CTRLAx.DONE bit in the LLI for that buffer. If the poll LLI.DMAC_CTRLAx.DONE bit is asserted,
then this buffer transfer has completed. This LLI.DMAC_CTRLAx.DONE bit was cleared at the start of the
transfer.
Note:
4.
5.
6.
7.
8.
9.