Digi Rabbit 5000, User Manual

Page: 239 / 414

Chapter 21 DMA Channels 239
21.3.5.1 Single Buffer
In the simplest mode, a single descriptor is set to halt and interrupt on completion.
21.3.5.2 Buffer Array
In this mode, an array of 12-byte descriptors is set up adjacent in memory; only the last
buffer is set to halt on completion. The last buffer is also typically set to interrupt on com-
pletion, but other buffer descriptors in the array can also generate interrupts.
The advantage of the buffer array is that its descriptors require less memory than a full 16-
byte descriptor.
The simplest version of the buffer array is a double buffer, which is frequently used to
provide a reserve buffer in case the application is slow in handling the first buffer once
received (in this case, both buffers are enabled to interrupt on completion).
Buffer Descriptor
(12 bytes)
Initial
Address
Single Buffer
Interrupt
Buffer Descriptor
(12 bytes)
Initial
Address
Buffer Array
Interrupt
Buffer Descriptor
(12 bytes)
Buffer Descriptor
(12 bytes)
Buffer Descriptor
(12 bytes)