Operation Theorem
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35
Bus-mastering DMA provides the fastest data transfer rate on PCI-
bus. Once the analog input operation starts, control returns to your
program. The hardware temporarily stores the acquired data in the
onboard A/D FIFO and then transfers the data to a user-defined
DMA buffer memory in the computer. Please note that even when
the acquiring data length is less than the FIFO, the AD data will not
be kept in the FIFO, but will be directly transfered to host memory
by bus-mastering DMA.
The DMA transfer mode is very complex to program. we
recommend using a high level program library to manipulate this
card. If you want to program the software which can handle the
DMA bus master data transfer, please refer to more information
about the PCI controller. (www. amcc. com. )
5.5.6
Host Memory Operation
Because of DMA data transfer, the AD data can not be
simultaneously processed when the data is transferred. Therefore,
user will have to process the AD data after the completion of one
DMA cycle. Please note that if the total data throughput in your
application is relatively high (>20MB/s), you with have to consider
that the processing of the AD data needs time and also consumes
the CPU computation power. There is limitation. For example, you
can not continuously acquire data at the rate of 20MB/s, but CPU
can only process the data at the rate of 10MB/s. In this case, the
FIFO will be full finally and the data acquisition will be discontinuous.
Storing the data in host memory into hard disk or other storage
device should be also considered. The burst data rate of current
HDD technology could be 90 up to 80MB/s. However, pratically the
HDD effective bandwidth is usually less than 10MB/s, especially
when the HDD seek time is longer, for example, 20 ms, the FIFO is
already full and the acquired data could not be continuous.
Another limitation comes from the OS and the host memory size.
Under DOS environment, the maximum memory size you can
allocate is less than 640K except that you use extended memory
managing software. Under Windows -95 or NT, it is quite hard to get
a continuously large size of memory such as 64M bytes, you have
to keep the memory “clean” , then there may be a chance to
allocate large size of memory. The PCI bus-mastering DMA
controller of PCI-9812 needs continuous memory to store the AD
data.
Summary of Contents for NuDAQ PCI-9812/10
Page 1: ...NuDAQ PCI 9812 10 20MHz Simultaneous 4 CH Analog Input Card Users Guide ...
Page 4: ......
Page 57: ...C C Library 49 ...
Page 61: ...Calibration 53 ...
Page 69: ...Software Utility 61 ...
