Dma Channel Assignments - Digi NS7520B-1-C36 Hardware Reference Manual

D M A c h a n n e l a s s i g n m e n t s
Buffer descriptor field definitions
Field
Source buffer pointer/Buffer
pointer
Status
Buffer length: Peripheral-to-
memory
Buffer length: Memory-to-
peripheral
Buffer length: Memory-to-
memory
Destination buffer pointer
Table 48: Buffer descriptor field definitions

DMA channel assignments

Any of the 13 channels in the DMA controller can be configured for memory-to-
memory mode. Those channels assigned to a peripheral (see Table 49, "DMA channel
assignments," on page 133) can be configured for fly-by mode.
1 3 2
Description
The source buffer pointer field identifies the starting location of the data
buffer. The source buffer pointer can start on any byte boundary for fly-by
memory-to-peripheral operations. The source buffer must be aligned on
32-bit boundaries to support peripheral-to-memory operations.
Peripherals can use the 16-bit status field to store transmit and receive
status words. The status field is updated when the current descriptor is
completed.
In fly-by peripheral-to-memory operations, indicates the maximum
number of bytes available in the receive buffer pointed to by the source
buffer pointer. After filling the receive buffer with peripheral data, the
DMA controller updates this field with the actual receive data byte count.
In fly-by memory-to-peripheral operations, indicates the number of bytes
to move to the peripheral device, pointed to by the source address pointer.
After completing the transfer, the DMA controller updates this field in a
transmit buffer descriptor with the actual data byte count (useful during
error conditions).
Indicates the number of bytes to move between the source and destination
locations. After completing a memory-to-memory transfer, the DMA
controller updates this field with the remaining data byte count (useful
during error conditions).
Used only when the DMA channel is configured for memory-to-memory
operations. The destination address pointer must start on the same byte
boundary as the source address pointer. If the source and destination byte
boundaries are different, the data operand size must be set for 8-bit
operations (see the SIZE field in "DMA Control register," beginning on
page 136).
N S 7 5 2 0 H a r d w a r e R e f e r e n c e , R e v G 9 / 2 0 0 7