ADLINK Technology NuDAQ PCI-9114DG, Руководство пользователя

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Operation Theorem
It’s recommend that users check your system to find out the user software‘s
priority in the special application. If the application software is at the highest
priority, polling the FIFO every 10 ms is suitable. However, the user‘s program
must check the FIFO is full or empty every time reading data.
To avoid this problem, the half-full polling method is used. If the A/D trigger
rate is 100KHz, the FIFO will be half-full (512 words) in 5.12 ms. If the user‘s
software checks the FIFO half full signal every 5 ms and the FIFO is not half-full,
the software does not read data. When the FIFO i s full, the AD FIFO is overrun.
That means the sampling rate is higher than users’ expect or the polling rate
is too slow. It is also possible due to your system occupy the CPU resource
thus reducing the polling rate. When the FIFO is half-full and not full, the
software can read one “block” (512 words) A/D data without checking the FIFO
status. This method is very convenient to read A/D in size of a “block” and it is
benefit to software programming.
Usually, the timer trigger is used under this mode, t herefore the sampling rate
is fixed. The method also utilizes the minimum CPU resources because it is
not necessary to be the highest priority. The other benefit is this method will
not use hardware interrupt resource. Therefore, the interrupt is reserved for
system clock or emergency external interrupt request. The FIFO half-full
polling method is the most powerful A/D data transfer mode.
EOC Interrupt Transfer
The PCI-9114 provides traditional hardware end-of-conversion (EOC)
interrupt capability. Under this mode, an interrupt signal is generated
when the A/D conversion is ended and the data is ready to be read in the
FIFO. It is useful to combine the EOC interrupt transfer with the timer
pacer trigger mode. After A/D conversion is completed, the hardware
interrupt will be inserted and its corresponding ISR (Interrupt Service
Routine) will be invoked and executed. The ISR program can read the
converted data. This method is most suitable for data processing
applications under real-time and fixed sampling rate
FIFO Half-Full Interrupt Transfer
Sometimes, the applications do not need real-time processing, but the
foreground program is too busy to poll the FIFO data. The FIFO half-full
interrupt transfer mode is useful for the situation mentioned above. In
addition, as the external A/D trigger source is used, the sampling rate
may be not easy to predict, and then the method could be applied.
Because the CPU is only interrupted when the FIFO is half-full, thus
reserved the CPU load.