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IDT DMA Controller
Internal DMA Operation
79RC32438 User Reference Manual
9 - 8
November 4, 2002
Notes
DEVCS is read from memory and transferred to the selected device. When a DMA descriptor operation
completes, updated status information is read from the selected device and written back to the DEVCS field
of the DMA descriptor in memory. The fourth word of a DMA descriptor, the link (LINK) field, contains the
physical address of the next DMA descriptor in a descriptor list (i.e., the next DMA descriptor in a linked list
of DMA descriptors).The link field is set to zero in the last descriptor within a descriptor list.
DMA Descriptor Register
Figure 9.4 DMA Descriptor Register
F
Finished.
This bit is set when the DMA controller finishes descriptor processing due to a finished
event (COUNT equal to zero). Note that this bit is not cleared if the condition did not occur. If this bit is
initially set in the Descriptor Register and the condition causing the DMA transaction to stop is not
related to this bit, then this bit will remain set in the DMA Descriptor written back to memory.
D
Done.
This bit is set when the DMA controller finishes descriptor processing due to a done event
(selected device generates done). Note that this bit is not cleared if the condition did not occur. If this
bit is initially set in the Descriptor Register and the condition causing the DMA transaction to stop is
not related to this bit, then this bit will remain set in the DMA Descriptor written back to memory.
T
Terminated.
This bit is set when DMA descriptor processing is abnormally terminated. This occurs
when the RUN bit in the DMA control register is cleared during a DMA operation, or when the bus
transaction timer times-out during a DMA bus transaction. Note that this bit is not cleared if the condi-
tion did not occur. If this bit is initially set in the Descriptor Register and the condition causing the DMA
transaction to stop is not related to this bit, then this bit will remain set in the DMA Descriptor written
back to memory.
IOD
Interrupt On Done.
When this bit is set, and the DMA controller finishes descriptor processing due to
a done event, then the D bit in the DMAxS register is set.
IOF
Interrupt On Finished.
When this bit is set, and the DMA controller finishes descriptor processing
due to a finished event, then the F bit in the DMAxS register is set.
COD
Chain On Done.
When this bit is set, and the DMA controller finishes descriptor processing due to a
done event, then the DMA controller loads the next descriptor pointed to by the DMAxNDPTR register.
COF
Chain On Finished.
When this bit is set and the DMA controller finishes descriptor processing due a
finished event, then the DMA controller loads the next descriptor pointed to by the DMAxNDPTR reg-
ister.
DEVCMD
Device Command.
This field is a device specific command field which is passed to the selected
device at the start of a DMA operation.
DS
Device Select.
This field selects the peripheral device used during the DMA descriptor operation. See
Table 9.2 on page 9-6 for the encoding of this field.
COUNT
Byte Count.
This field specifies the number of bytes to transfer during the DMA descriptor operation.
CA
Current Address.
This 32-bit field is initialized with the DMA starting address at the start of a DMA
operation and is updated when descriptor processing is completed.
CA
F
D
IOD
IOF
COD COF
1
1
1
1
1
1
DEVCMD
DS
COUNT
DEVCS
LINK
T
1
18
3
2
reserved
2