ATS9360 User Manual
35
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
Frequency (PRF) of 1 KHz or so, even though each capture
is only 2048 bytes (a paltry 2 MB/s throughput).
In other words, digitizers that specify raw data throughput of
100 MB/s can hardly handle 2MB/s effective throughput due
to operating system related delays in issuing re-arm
commands.
