Generic Channels
5-9
System DMA Controller
5.3
Generic Channels
This section discusses the following generic channel topics:
-
Transfers
-
Addressing modes
-
Data packing and bursting
-
Data alignment
-
Constraint on channel configuration parameters
-
Endianism
-
Interrupt generation
-
Memory space protection
5.3.1
Transfers
5.3.1.1
Transfer Sources and Destination
Each DMA channel can be configured independently from other channels.
This implies that a port can be shared by several channel requests. Therefore,
these requests are time-multiplexed by the port.
For example, in Figure 5–4 a DMA port must service requests from three DMA
channels:
-
Channel 0 as a source port (read requests, r
0
)
-
Channel 3 as a destination port (write requests, w
3
)
-
Channel 5 as a destination port (write requests. w
5
)
Figure 5–4 shows how these requests are multiplexed in time by the port.
Figure 5–4. Time-Sharing on a DMA Port
r
0
, r
0
, r
0
Requests
waiting for
service
Port
w
3
, w
3
, w
3
w
5
, w
5
, w
5
w
5
, w
3
, r
0
, w
5
, w
3
, r
0
, w
5
, w
3
, r
0
Requests served
A system DMA port can handle 10 read requests and 10 write requests (all the
possible requests in the DMA) simultaneously.