• SARn and DARn change after each data transfer depending on DCRn[SSIZE,
DSIZE, SINC, DINC, SMOD, DMOD] and the starting addresses. Increment
values can be 1, 2, or 4 for 8-bit, 16-bit, or 32-bit transfers, respectively. If the
address register is programmed to remain unchanged, the register is not
incremented after the data transfer.
• BCRn[BCR] must be loaded with the total number of bytes to be transferred. It
is decremented by 1, 2, or 4 at the end of each transfer, depending on the transfer
size. DSRn[DONE] must be cleared for channel startup.
• After the channel has been initialized, it may be started by setting DCRn[START] or
a properly selected peripheral DMA request, depending on the status of
DCRn[ERQ]. For a software-initiated transfer, the channel can be started by setting
DCRn[START] as part of a single 32-bit write to the last 32 bits of the TCDn; that is,
it is not required to write the DCRn with START cleared and then perform a second
write to explicitly set START.
• Programming the channel for a software-initiated request causes the channel to
request the system bus and start transferring data immediately. If the channel is
programmed for peripheral-initiated request, a properly selected peripheral DMA
request must be asserted before the channel begins the system bus transfers.
• The hardware can automatically clear DCRn[ERQ], disabling the peripheral request,
when BCRn reaches zero by setting DCRn[D_REQ].
• Changes to DCRn are effective immediately while the channel is active. To avoid
problems with changing a DMA channel setup, write a one to DSRn[DONE] to stop
the DMA channel.
23.4.3 Dual-Address Data Transfer Mode
Each channel supports dual-address transfers. Dual-address transfers consist of a source
data read and a destination data write. The DMA controller module begins a dual-address
transfer sequence after a DMA request. If no error condition exists, DSRn[REQ] is set.
• Dual-address read—The DMA controller drives the SARn value onto the system
address bus. If DCRn[SINC] is set, the SARn increments by the appropriate number
of bytes upon a successful read cycle. When the appropriate number of read cycles
complete (multiple reads if the destination size is larger than the source), the DMA
initiates the write portion of the transfer.
If a termination error occurs, DSRn[BES, DONE] are set and DMA transactions stop.
Chapter 23 DMA Controller Module
KL25 Sub-Family Reference Manual, Rev. 3, September 2012
Freescale Semiconductor, Inc. 363
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