Functional Description
604
SLAU723A – October 2017 – Revised October 2018
Copyright © 2017–2018, Texas Instruments Incorporated
Micro Direct Memory Access (µDMA)
Table 8-2. Control Structure Memory Map
Offset
Channel
0x0
0, Primary
0x10
1, Primary
...
...
0x1F0
31, Primary
0x200
0, Alternate
0x210
1, Alternate
...
...
0x3F0
31, Alternate
summarizes 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 8-3. Channel Control Structure
Offset
Description
0x000
Source End Pointer
0x004
Destination End Pointer
0x008
Control Word
0x00C
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
. 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 reconfigured before each new transfer. The source and destination end
pointers are not modified, so they can be left unchanged if the source or destination addresses remain the
same.
Before starting a transfer, a µDMA channel must be enabled by setting the appropriate bit in the DMA
Channel Enable Set (DMAENASET) register. A channel can be disabled by setting the channel bit in the
DMA Channel Enable Clear (DMAENACLR) register. At the end of a complete µDMA transfer, the
controller automatically disables the channel.
8.3.5 Transfer Modes
The µDMA controller supports several transfer modes. Two of the modes support simple one-time
transfers. Several complex modes support a continuous flow of data.
8.3.5.1
Stop Mode
While Stop is not actually a transfer mode, it is a valid value for the mode field of the control word. When
the mode field has this value, the µDMA controller does not perform any transfers and disables the
channel if it is enabled. At the end of a transfer, the µDMA controller updates the control word to set the
mode to Stop.