BitFlow Cyton-CXP, Hardware Reference Manual

Page: 72 / 388

The Buffer Manager Details The Cyton-CXP
CYT-3-2 BitFlow, Inc. Version A.0
3.2 The Buffer Manager Details
The Buffer Manager interacts with a remote, software managed, set of Scatter Gather
DMA lists. A single Scatter Gather DMA list is called a QTab. A QTab is made of indi-
vidual DMA instructions (descriptors) called Quads. One Quad contains the informa-
tion to DMA one contiguous chunk of data from the board to host memory. The Buffer
Manager reads in and precaches QTabs and the associated Quads. It makes the
cached Quads and QTabs available to the Acquisition Engine in queued order. The
Buffer Manager works independently of the Acquisition Engine and can be throttled
by software.
The Buffer Manager and Acquisition Engine are designed to work asynchronously
from each other. The Buffer Manager is capable of reading in Quads from the remote
QTab while the Acquisition Engine is Running/Stopping/Aborting/or Stopped. If the
local Buffer Cache fills and the Acquisition Engine is not currently consuming Quads,
the Buffer Manager simply waits until room becomes available and pauses loading
Quads from the remote QTab. Likewise, the Acquisition Engine is capable of acquir-
ing frames as long as it is running and has Quad available to work on. If no Quad are
available it will simply wait for more to become available from the Buffer Manager.
The Acquisition Engine can accept commands of Stop/Abort/Start, all while the Buffer
Manager is running independently.
The starting, stopping, and restarting of the Acquisition Engine and Buffer Manager,
however, does require some synchronization. The Buffer Manager pre-fetches Quad
and Quads for efficiency. This built up pipeline and caching structure requires the
Acquisition Engine to be in the Stopped state before the Buffer Manager can be
safely flushed. Flushing of the Buffer Manager happens when the user wants to com-
pletely shut down the StreamSync Acquisition Engine or simply start acquiring to a
new QTab.