AlazarTech ATS9462, Руководство пользователя

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ATS9462 User Manual 43
Streaming Using Data FIFO
One of the most unique features of the ATS9462 is its on-
FPGA Data FIFO and the associated Dual-DMA engine. 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 Linux are not real-time operating systems, i.e.
the operating system cannot guarantee a deterministic
response time to an event, such as an interrupt 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.
For example, it is very common for PCI digitizers that boast
very fast throughput to slow down considerably when
capturing pulsed radar or ultrasonic signals at Pulse Repeat