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Starting DMA Transfer: The following registers exist to control DMA transfers: DMA transfer
arbitration register (PCIDMABT) and, for four channels, the DMA transfer PCI address register
[3:0] (PCIDPA [3:0]), DMA transfer local bus starting address register [3:0] (PCIDLA [3:0]),
DMA transfer count register [3:0] (PCIDTC [3:0]), and DMA control register [3:0] (PCIDCR
[3:0]).
Set the arbitration mode in PCIDMABT prior to starting the DMA transfer. Also select the DMA
channel to be used, set the PCI bus starting address and local bus starting address in the
appropriate PCIDPA and PCIDLA for the selected channel, respectively, set the number of bytes
in the transfer in PCIDTC, set the DMA transfer mode in the PCIDCR, and specify a transfer start
request.
The transfer starting address and the number of bytes in the transfer can be set on byte or word
boundaries, but because the least significant two bits of these registers are ignored, the transfer is
performed in longword units. Also, note that the local bus starting address set in PCIDLA is the
physical address.
PCIDPA, PCIDLA, and PCIDTC are updated during data transfer. If another DMA transfer is to
be performed on completion of one DMA transfer, new values must be set in these registers.
The registers controlling DMA transfers can be set from both CPU and PCI device. Note that the
DMA channel allocated to the CPU and PCI device must be predetermined when configuring the
system.
When performing DMA transfers, the address of the local bus and the size of data to be transferred
can be set to a 32-byte boundary to ensure that data transfers on the local bus are as efficient as
possible.
PCIDCR can be used to control the abortion of DMA transfers, the direction of DMA transfers, to
select PCI commands (memory/I/O) whether to update the PCI address, whether to update the
local address, whether to use transfer termination interrupts, and, when the local bus is big endian,
the method of alignment.
Figure 22.5 shows an example of DMA transfer control register settings.
Rev. 3.0, 04/02, page 892 of 1064
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