DMA Operation
349
SLAU367P – October 2012 – Revised April 2020
Copyright © 2012–2020, Texas Instruments Incorporated
DMA Controller
11.2.4 Halting Executing Instructions for DMA Transfers
The DMARMWDIS bit controls when the CPU is halted for DMA transfers. When DMARMWDIS = 0, the
CPU is halted immediately and the transfer begins when a trigger is received. In this case, it is possible
that CPU read-modify-write operations can be interrupted by a DMA transfer. When DMARMWDIS = 1,
the CPU finishes the currently executing read-modify-write operation before the DMA controller halts the
CPU and the transfer begins (see
Table 11-2. DMA Trigger Operation
Module
Operation
DMA
A transfer is triggered when the DMAREQ bit is set. The DMAREQ bit is automatically reset when the transfer
starts.
A transfer is triggered when the DMAxIFG flag is set. DMA0IFG triggers channel 1, DMA1IFG triggers channel 2,
and DMA2IFG triggers channel 0. None of the DMAxIFG flags are automatically reset when the transfer starts.
A transfer is triggered by the external trigger DMAE0.
Timer_A
A transfer is triggered when the TAxCCR0 CCIFG flag is set. The TAxCCR0 CCIFG flag is automatically reset
when the transfer starts. If the TAxCCR0 CCIE bit is set, the TAxCCR0 CCIFG flag does not trigger a transfer.
A transfer is triggered when the TAxCCR2 CCIFG flag is set. The TAxCCR2 CCIFG flag is automatically reset
when the transfer starts. If the TAxCCR2 CCIE bit is set, the TAxCCR2 CCIFG flag does not trigger a transfer.
Timer_B
A transfer is triggered when the TBxCCR0 CCIFG flag is set. The TBxCCR0 CCIFG flag is automatically reset
when the transfer starts. If the TBxCCR0 CCIE bit is set, the TBxCCR0 CCIFG flag does not trigger a transfer.
A transfer is triggered when the TBxCCR2 CCIFG flag is set. The TBxCCR2 CCIFG flag is automatically reset
when the transfer starts. If the TBxCCR2 CCIE bit is set, the TBxCCR2 CCIFG flag does not trigger a transfer.
eUSCI_Ax
A transfer is triggered when eUSCI_Ax receives new data. UCAxRXIFG is automatically reset when the transfer
starts. If UCAxRXIE is set, the UCAxRXIFG does not trigger a transfer.
A transfer is triggered when eUSCI_Ax is ready to transmit new data. UCAxTXIFG is automatically reset when
the transfer starts. If UCAxTXIE is set, the UCAxTXIFG does not trigger a transfer.
eUSCI_Bx
A transfer is triggered when eUSCI_Bx receives new data. UCBxRXIFG is automatically reset when the transfer
starts. If UCBxRXIE is set, the UCBxRXIFG does not trigger a transfer.
A transfer is triggered when eUSCI_Bx is ready to transmit new data. UCBxTXIFG is automatically reset when
the transfer starts. If UCBxTXIE is set, the UCBxTXIFG does not trigger a transfer.
ADC12_B
A transfer is triggered by an ADC12IFG flag. When single-channel conversions are performed, the
corresponding ADC12IFG is the trigger. When sequences are used, the ADC12IFG for the last conversion in the
sequence is the trigger. A transfer is triggered when the conversion is completed and the ADC12IFG is set.
Setting the ADC12IFG with software does not trigger a transfer. All ADC12IFG flags are automatically reset
when the associated ADC12MEMx register is accessed by the DMA controller.
MPY
A transfer is triggered when the hardware multiplier is ready for a new operand.
Reserved
No transfer is triggered.
11.2.5 Stopping DMA Transfers
There are two ways to stop DMA transfers in progress:
•
A single, block, or burst-block transfer may be stopped with an NMI, if the ENNMI bit is set in register
DMACTL1.
•
A burst-block transfer may be stopped by clearing the DMAEN bit.
11.2.6 DMA Channel Priorities
The default DMA channel priorities are DMA0 through DMA7. If two or three triggers happen
simultaneously or are pending, the channel with the highest priority completes its transfer (single, block, or
burst-block transfer) first, then the second priority channel, then the third priority channel. Transfers in
progress are not halted if a higher-priority channel is triggered. The higher-priority channel waits until the
transfer in progress completes before starting.
The DMA channel priorities are configurable with the ROUNDROBIN bit. When the ROUNDROBIN bit is
set, the channel that completes a transfer becomes the lowest priority. The order of the priority of the
channels always stays the same, DMA0-DMA1-DMA2, for example, for three channels. When the
ROUNDROBIN bit is cleared, the channel priority returns to the default priority.