LM3S2276 Datasheet, PDF (292/785 Pages) Texas Instruments – Stellaris® LM3S2276 Microcontroller

Micro Direct Memory Access (μDMA)
8.2.6
8.2.6.1
8.2.6.2
8.2.6.3
8.2.6.4
Transfer Modes
The μDMA controller supports several transfer modes. Two of the modes support simple one-time
transfers. There are several complex modes that are meant to support a continuous flow of data.
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 will not perform a transfer and will disable
the channel if it is enabled. At the end of a transfer, the μDMA controller will update the control word
to set the mode to Stop.
Basic Mode
In Basic mode, the μDMA controller will perform transfers as long as there are more items to transfer
and a transfer request is present. This mode is used with peripherals that assert a DMA request
signal whenever the peripheral is ready for a data transfer. Basic mode should not be used in any
situation where the request is momentary but the entire transfer should be completed. For example,
for a software initiated transfer, the request is momentary, and if Basic mode is used then only one
item will be transferred on a software request.
When all of the items have been transferred using Basic mode, the μDMA controller will set the
mode for that channel to Stop.
Auto Mode
Auto mode is similar to Basic mode, except that once a transfer request is received the transfer will
run to completion, even if the DMA request is removed. This mode is suitable for software-triggered
transfers. Generally, you would not use Auto mode with a peripheral.
When all the items have been transferred using Auto mode, the μDMA controller will set the mode
for that channel to Stop.
Ping-Pong
Ping-Pong mode is used to support a continuous data flow to or from a peripheral. To use Ping-Pong
mode, both the primary and alternate data structures are used. Both are set up by the processor
for data transfer between memory and a peripheral. Then the transfer is started using the primary
control structure. When the transfer using the primary control structure is complete, the μDMA
controller will then read the alternate control structure for that channel to continue the transfer. Each
time this happens, an interrupt is generated and the processor can reload the control structure for
the just-completed transfer. Data flow can continue indefinitely this way, using the primary and
alternate control structures to switch back and forth between buffers as the data flows to or from
the peripheral.
Refer to Figure 8-2 on page 293 for an example showing operation in Ping-Pong mode.
292
November 17, 2011
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