User's Manual Part 2

Host Computer Commands
RVP8 User’s Manual
May 2003
6–2
The sequence of events described above is altered when the FIFO becomes completely full.
Then, 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. Until this space becomes available,
the RVP8 simply waits and does not proceed any further with its internal processing. This, of
course, leads to a slowdown in performance, but it is not a disastrous one. The user always
obtains correct data no matter how long it takes to read it. One could take advantage of this fact
to synchronize the acquisition of data by the RVP8 with the post-processing and display of that
data by the user. In this case, RVP8 would be instructed to output data at the maximum rate, the
user would read these words at the user’s maximum rate, and the overall system would
automatically run at the slower of those two speeds.
When the output FIFO is full and the RVP8 has the next word ready for output, there is another
way that the idle wait loop can be exited, that is, 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 taken to mean that some more important condition has arisen. As such, the
wait loop is terminated and the RVP8 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 net effect is that the processor continues to execute all commands correctly,
but that their output is discarded.
The discarded output data are not in fact lost. Rather, the data are eventually replaced with an
equal number of zeros. Each time the RVP8 discards an output word, it also increments an
internal 24-bit count. When FIFO space becomes available in the future, the processor replaces
all of the missing data with zero-valued placeholders.
Writing when the FIFO is full can be particularly useful if the new command is a RESET which
calls for clearing of the output FIFO. When the RESET is processed, all past and present output
data are discarded, leaving the RVP8 output section completely empty. This is useful whenever
the processor has pending output data which the user wants to truly throw away.
6.1 No-Operation (NOP)
This single-word instruction is simply ignored by the the Signal Processor. The NOP is useful
when a number of words are to be flushed through the RVP8 with no side effects.
15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0
| | | | | | | | | | | | | | | | |
| | 0 0 0 0 0 | Command
|___________________________________________|___________________|
6.2 Load Range Mask (LRMSK)
This command informs the signal processor of the ranges at which data are to be collected. An
arbitrary set of range bins are selected via an 8192-bit mask. The Nth bit in the mask determines
whether data are acquired and processed at a range equal to RES x (N-1). The Range resolution
is specified by a TTY setup question (see section 3.3.5), in the range 50 through 133 meters.
Any collection of ranges may be chosen from integer multiples of that distance. The example
below is given for the default resolution of 125 meters. The range mask is passed to the RVP8