LM3S1621 Datasheet, PDF (343/947 Pages) Texas Instruments – ARM and Thumb are registered trademarks and Cortex is a trademark

Stellaris^® LM3S1621 Microcontroller
necessary, 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 8-3. Control Structure Memory Map
Offset
0x0
0x10
...
0x1F0
0x200
0x210
...
0x3F0
Channel
0, Primary
1, Primary
...
31, Primary
0, Alternate
1, Alternate
...
31, Alternate
Table 8-4 shows an individual control structure entry in the control table. Each entry is aligned on
a 16-byte boundary. The entry contains four long words: the source end pointer, the destination end
pointer, the control word, and an unused entry. The end 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 8-4. Channel Control Structure
Offset
0x000
0x004
0x008
0x00C
Description
Source End Pointer
Destination End Pointer
Control Word
Unused
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
■ Transfer mode
The control word and each field are described in detail in “μDMA Channel Control
Structure” on page 360. The μDMA controller updates the transfer size and transfer mode fields as
the transfer is performed. At the end of a transfer, the transfer size indicates 0, and the transfer
mode indicates "stopped." Because the control word is modified by the μDMA controller, it must be
January 21, 2012
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