Motorola PowerQUICC II MPC8280 Series Reference Manual page 686

IDMA Transfers
External request mode does not support external DONE
signaling from a device and DACK signaling from an IDMA
channel.
19.5.1.2 Normal Mode
When external request mode is not selected (DCM[ERM] = 0), the IDMA channel operates
automatically, ignoring DREQ.
19.5.1.3 Working with a PCI Bus
When working to/from the PCI bus (multiplexed with the local bus), the data usually comes
on the bus in one long burst. The alignment policy described above to support 60x/local bus
bursts does not affect its efficiency.
19.5.2 Memory to/from Peripheral Transfers
Working with peripheral devices requires the external signals DONE, DREQ, DACK to
control the data transfer using the following rules:
• The peripheral sets a request for data to be read-from/write-to by asserting DREQ
as configured, falling or rising edge sensitive.
• The peripheral transfers/samples the data when DACK is asserted.
• The peripheral asserts DONE to stop the current transfer.
• The peripheral terminates the current transfer when DONE is asserted, combined
with DACK, by the IDMA.
Peripherals are usually accessed with fixed port-size transfers. The transfer sizes
(STS/DTS) related to the peripheral must be programmed to its port size; thus, every access
to a peripheral yields a single bus transaction. The maximum peripheral port size is
(bus_width - 8) bytes and also should evenly divide the buffer length, BD[Data Length].
A peripheral can also be configured to accept a burst per DREQ assertion. In this case, the
transfer size parameter should be initialized to 32, and the accesses are made in bursts. See
Table 19-8.
A peripheral can be accessed at a fixed address location or at incremental addresses. Setting
DCM[SINC, DINC] in the DMA channel mode register causes the address to be
incremented before the next transfer; see Section 19.8.2.1, "DMA Channel Mode (DCM)."
This allows the IDMA to access a FIFO buffer the same way it does peripherals.
DCM[S/D] determines whether the peripheral is the source or destination.
19-10
Freescale Semiconductor, Inc.
NOTE
MPC8280 PowerQUICC II Family Reference Manual
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA