Copyright © 2020
Alazar Technologies Inc.
54
ATS9353 User Manual
Streaming Data Across the Bus
One of the most unique features of the ATS9353 is its on-board, dual-port
acquisition memory, with custom Direct Memory Access (DMA), that can be used
for signal storage.
Data is acquired into the on-board memory before being transferred to the host
PC memory. This transfer is performed using custom DMA, which uses scatter-
gather bus mastering technology. This on-board dual-port memory allows loss-
less data transfer even if the computer is temporarily interrupted by other tasks.
This combined by the advanced, fully asynchronous software driver allows data
transfer to host PC memory without any appreciable “in-process” software
involvement.
These features are particularly useful for applications that require:
a)
Continuous, gapless data capture. Also known as “Data Streaming” to PC
host memory or hard disk
or
b)
Data capture from rapidly occurring triggers, also known as Pulse Repeat
Frequency Captures or PRF Captures.
In order to understand these sophisticated features, let us first review some of
the issues involved in transferring data under Windows or Linux operating
systems.
The Effects of the Operating System
Windows and most Linux distributions are not real-time operating systems, i.e.
the operating system cannot guarantee a deterministic response time to an
event, such as an interruption or a software-generated event.
This means that if software has to play any appreciable part in data transfer,
then the data throughput cannot be guaranteed, as the operating system will
have the last say as to when the data collection application will get the CPU
cycles to execute the necessary commands.
Note that the above is true even if the digitizer claims to use Direct Memory
Access (DMA) to do the actual transfer, but uses software commands to re-arm
the digitizer. It is the re-arm command that will determine the overall data
throughput.