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TC1784
Direct Memory Access Controller (DMA)
User´s Manual
11-14
V1.1, 2011-05
DMA, V3.03
Hardware-controlled Modes
In hardware-controlled modes, a hardware request signal starts a DMA transaction or a
single DMA transfer. There are two hardware-controlled modes available:
•
Single Mode:
Hardware requests are disabled by hardware after a DMA transaction
•
Continuous Mode:
Hardware requests are not disabled by hardware after a DMA transaction
Hardware-controlled Single Mode
In hardware-controlled Single Modes, one hardware request starts one complete DMA
transaction or one single DMA transfer. The hardware-controlled Single Mode that
initiates one complete DMA transaction to be executed for DMA channel mn is selected
by the following operations:
•
CHCRmn.CHMODE = 0
•
CHCRmn.RROAT = 1
•
Selecting one of the sixteen hardware request inputs via CHCRmn.PRSEL
•
HTREQ.ECHmn = 1
Setting HTREQ.ECHmn to 1 causes the hardware request CHmn_REQ of channel mn
to be enabled (TRSR.HTREmn = 1). Whenever the hardware request CHmn_REQ
becomes active, the value of CHCRmn.TREL is loaded into CHSRmn.TCOUNT and the
DMA transaction is started by executing its first DMA transfer. After each DMA transfer,
TCOUNT becomes decremented and next source and destination addresses are
calculated. When TCOUNT reaches the 0, DMA channel 0n becomes disabled and
status flags TRSR.CHmn and TRSR.HTREmn are reset. In order to start a new
hardware-controlled DMA transaction, hardware requests must be enabled again by
setting TRSR.HTREmn through HTREQ.ECHmn = 1. The hardware request disable
function in Single Mode is typically needed when a reprogramming of the DMA channel
register set (addresses, transfer count) is required before the next hardware triggered
DMA transaction is started.
The hardware-controlled Single Mode in which each single DMA transfer has to be
requested by a hardware request signal is selected as described above, with one
difference:
•
CHCRmn.RROAT = 0
In this operation mode, TRSR.CHmn becomes reset after each DMA transfer of the DMA
transaction, and a new hardware request at CHmn_REQ must be generated for starting
the next DMA transfer.
Содержание TC1784
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