Functional Description
MSC8144E Reference Manual, Rev. 3
Freescale Semiconductor
17-5
17.2.1.1.1 Basic Direct Mode
In basic direct mode, the DMA controller does not read descriptors from memory, but instead
uses the current parameters programmed in the DMA registers to start the DMA transfer.
Software is responsible for initializing SARn, SATRn, DARn, DATRn, and BCRn registers. The
DMA transfer is started when MRn[CS] is set. Software is expected to program all the
appropriate registers before setting MRn[CS] to a 1. The transfer is finished after all the bytes
specified in the byte count register have been transferred or if an error condition occurs. The
sequence of events to start and complete a transfer in basic direct mode is as follows:
1.
Poll the channel state (see Table 17-2), to confirm that the specific DMA channel is
idle.
2.
Initialize SARn, SATRn, DARn, DATRn and BCRn.
3.
Set the mode register channel transfer mode bit, MRn[CTM], to indicate direct mode.
Other control parameters may also be initialized in the mode register.
4.
Clear then set the mode register channel start bit, MRn[CS], to start the DMA transfer.
5.
SRn[CB] is set by the DMA controller to indicate the DMA transfer is in progress.
6.
SRn[CB] is automatically cleared by the DMA controller after the transfer is finished, or
if the transfer is aborted (MRn[CA] transitions from a 0 to 1), or if a transfer error
occurs.
7.
End of segment interrupt is generated if MRn[EOSIE] is set.
17.2.1.1.2 Basic Direct Single-Write Start Mode
In basic direct single-write start mode, the DMA controller does not read descriptors from
memory, but instead uses the current parameters programmed in the DMA registers to start the
DMA transfer. Software is responsible for initializing the SATRn, DATRn, and BCRn registers.
Setting MRn[SRW] configures the DMA controller to begin the DMA transfer either when SARn
is written or when DARn is written, determined by the state of MRn[CDSM/SWSM]. Writing to
SARn initiates the DMA transfer if MRn[CDSM/SWSM] is set. Writing to DARn initiates the
DMA transfer if MRn[CDSM/SWSM] is cleared. The DMA controller automatically sets the
channel start bit, MRn[CS]. Software is expected to program all the appropriate registers before
writing the source or destination address registers. The transfer is finished after all the bytes
specified in the byte count register have been transferred or if an error condition occurs. The
sequence of events to start and complete a transfer in single-write start basic direct mode is as
follows:
1.
Poll the channel state (see Table 17-2), to confirm that the specific DMA channel is
idle.
2.
Initialize the source attributes (SATRn), DATRn, and BCRn registers.
Содержание MSC8144E
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