Motorola PowerQUICC II MPC8280 Series Reference Manual page 414

DMA Controller
9.13.1.1 DMA Direct Mode
In direct mode, the DMA controller does not read a chain of descriptors from memory but
instead uses the current parameters in the DMA registers to start a DMA transfer. The DMA
transfer finishes after all the bytes specified in the byte count register have been transferred
or an error condition has occurred. Below are the initialization steps of a DMA transfer in
direct mode.
• Poll the CB (channel busy) bit in the status register to make sure the DMA channel
is idle (refer to Section 9.13.1.6.2, "DMA Status Registers 0–3 (DMASRx)").
• Initialize the source, destination and byte count register (refer to Section 9.13.1.6.5,
"DMA Destination Address Registers 0–3 (DMADARx)," and Section 9.13.1.6.6,
"DMA Byte Count Registers 0–3 (DMABCRx)").
• Initialize the CTM (channel transfer mode) bit in the mode register (refer to
Section 9.13.1.6.1, "DMA Mode Registers 0–3 (DMAMRx)") to indicate direct
mode. Other control parameters in the mode register can also be initialized here if
necessary.
• First clear then set the CS (channel start) bit in the mode register to start the DMA
transfer.
9.13.1.2 DMA Chaining Mode
In chaining mode, the DMA controller loads descriptors from memory prior to a DMA
transfer. The DMA controller begins the transfer according to the descriptor information
loaded for each segment. Once the current segment is finished, the DMA controller reads
the next descriptor from memory and begins another DMA transfer. The process is finished
if the current descriptor is the last one in the chain or an error condition has occurred. Below
are the initialization steps of a DMA transfer in chaining mode.
• Build a chain of descriptor segments in memory. Refer to the Section 9.13.2, "DMA
Segment Descriptors," for more information.
• Poll the CB (channel busy) bit in the status register to make sure the DMA channel
is idle.
• Initialize the current descriptor address register to point to the first descriptor in the
chain.
• Initialize the CTM (channel transfer mode) bit in the mode register to indicate
chaining mode. Other control parameters in the mode register can also be initialized
here if necessary.
• First clear then set the CS (channel start) bit in the mode register to start the DMA
transfer.
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