Vaisala RVP900, Руководство пользователя

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8. When the setups are complete, issue
PROC
commands to collect, process, and output
the data.
To monitor errors detected during the execution of commands using the GPARM
command.
8.1.2 First-in-first-out (FIFO) buffer
RVP900 contains a 4096-word first-in-first-out (FIFO) buffer through which all output data
flow.
The FIFO holds each sequential word generated by RVP900 until the user is ready to accept
it. When reading from the processor, the host can fall behind by as many as 4096 words
before performance slows.
RVP900 writes to the FIFO at full speed as long as it is not full. Internal processing is not
affected by the exact speed at which user I/O occurs.
Writing to the FIFO continues as long as the average I/O rate on, perhaps 10 ms intervals,
and matches the average rate at which data are being produced.
Full Output FIFO
The sequence of events changes when the FIFO is full:
1. When the processor generates the next output word, it waits in an idle loop until the
user makes room in the FIFO by reading out one or more words.
2. RVP900 waits and does not proceed with its internal processing until space becomes
available.
Despite the slowdown in performance, you always obtain correct data no matter how long it
takes to read it. You can take advantage of this to synchronize the acquisition of data by the
RVP900 with the post-processing and display of that data by the user.
In this case, RVP900 would be instructed to output data at the maximum rate, you can read
these words at your maximum rate, and the overall system automatically runs at the slower
of those two speeds.
Write Cycle and Full Output FIFO
If the output FIFO is full and the RVP900 has the next word ready for output, the idle wait
loop can be exited if the processor detects that the user is performing a write I/O cycle.
Since the user should have been reading data by now, the presence of a write cycle is
understood to mean that a more important condition has arisen. The wait loop terminates
and RVP900 accepts the write data soon afterward. If the new data are commands, they are
executed right away, but any output they try to produce may be lost in a similar manner. The
processor continues to execute all commands correctly, but that their output is discarded.
RVP900 User Guide M211322EN-J
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