CH2
CH4
CH5
CH7
CH1
CH3
CH6
C
H
1
CH
3
CH
7
CH
9
C
H
1
3
CH
15
C
H
2
C
H
4
C
H
6
C
H
8
C
H
1
0
CH14
in qu eue
i
n u se
Pendin g trigg ere d
Start/S top se rv in g
CH2
CH4
CH5
CH7
CH1
CH3
CH6
C
H
1
CH
3
CH
7
CH
9
C
H
1
3
CH
15
C
H
2
C
H
4
C
H
6
C
H
8
C
H
1
0
CH14
in qu eue
i
n u se
CH2
CH4
CH5
CH7
CH1
CH3
CH6
C
H
1
CH
3
CH
7
CH
9
C
H
1
3
CH
15
C
H
2
C
H
4
C
H
6
C
H
8
C
H
1
0
CH14
High
queue
Low
queue
Fixed
Rotation
in queue
in use
in queue
in use
Module Operation
549
SPNU503C – March 2018
Copyright © 2018, Texas Instruments Incorporated
Direct Memory Access Controller (DMA) Module
Table 16-1. Arbitration According to Priority Queues and Priority Schemes
Queue
Priority Scheme
Remark
High priority
Fixed
Channels are serviced in an ascending order according to the channel number.
The lower the channel number, the higher the priority. A channel will be
arbitrated out whenever there is a higher pending channel. Otherwise a channel
is completely serviced until its transfer count reaches zero before the next
highest pending channel is serviced. When there is no pending channels left in
high queue then the DMA switches to service low queue channels.
Rotating
Channels are arbitrated by using the round-robin scheme. Arbitration is
performed when the FIFO is empty. When there are no pending channels left in
high queue then the DMA switches to service low queue channels.
Low priority
Fixed
Channels are serviced in an ascending order according to the channel number.
The lower the channel number the higher the priority. A channel will be arbitrated
out whenever there is a higher-priority pending channel. Otherwise a channel is
completely serviced until its transfer count reaches zero, before the next highest
pending channel is serviced. If there is a pending channel in the high-priority
queue while DMA is servicing a low queue channel then DMA will switch back to
service high queue channel after an arbitration boundary.
Rotating
Channels are arbitrated by using round-robin scheme. Arbitration is performed
when the FIFO is empty.
A Simple Priority Queues example in both Fixed and Rotation Scheme is shown in
.
Figure 16-10. Example of Priority Queues