LM3S3739 Luminary Micro, Inc, LM3S3739 Datasheet - Page 184

• Manufacturer Part Number: LM3S3739
• Description: Lm3s3739 Arm Microcontroller
• Manufacturer: Luminary Micro, Inc

Micro Direct Memory Access (μDMA)
184
Table 9-3 on page 184 shows the layout in memory of the channel control table. Each channel may
have one or two control structures in the contol table: a primary control structure and an optional
alternate control structure. The table is organized so that all of the primary entries are in the first
half of the table and all the alternate structures are in the second half of the table. The primary entry
is used for simple transfer modes where transfers can be reconfigured and restarted after each
transfer is complete. In this case, the alternate control structures are not used and therefore only
the first half of the table needs to be allocated in memory. The second half of the control table is
not needed and that memory can be used for something else. If a more complex transfer mode is
used such as ping-pong or scatter-gather, then the alternate control structure is also used and
memory space should be allocated for the entire table.
Any unused memory in the control table may be used by the application. This includes the control
structures for any channels that are unused by the application as well as the unused control word
for each channel.
Table 9-3. Control Structure Memory Map
Table 9-4 on page 184 shows an individual control structure entry in the control table. Each entry
has a source and destination end pointer. These pointers point to the ending address of the transfer
and are inclusive. If the source or destination is non-incrementing (as for a peripheral register), then
the pointer should point to the transfer address.
Table 9-4. Channel Control Structure
The remaining part of the control structure is the control word. The control word contains the following
fields:
■
■
■
■
■
Source and destination data sizes
Source and destination address increment size
Number of transfers before bus arbitration
Total number of items to transfer
Useburst flag
Offset
0x00C
0x000
0x004
0x008
Offset
0x1F0
0x200
0x210
0x3F0
0x10
0x0
...
...
Description
Source End Pointer
Destination End Pointer
Control Word
Unused
Channel
0, Primary
1, Primary
...
31, Primary
0, Alternate
1, Alternate
...
31, Alternate
Preliminary
June 02, 2008