Subject:
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RE: NQC versus Lego RCX Code Speed
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Newsgroups:
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lugnet.robotics
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Date:
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Thu, 5 Oct 2000 16:21:22 GMT
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Original-From:
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Mark Pulver <mark@AVOIDSPAMmidiwall.com>
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Viewed:
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544 times
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Wilcox, Doug (11:04 AM 10.05.2000) wrote:
>Hmm. This question seems to have gone the way of my PC-->IR Tower cable
>question.
>
>Let me try to get at the point that most interests me--what is the
>difference, at the RCX level, between programs coded in NQC and programs
>coded in RCX Code. Is the compiled NQC code closer to the "machine level"?
I don't know for sure, but I would think that the RCX code is actually
P-Code (Pseudo Code) and what's really running in the RCX itself is a
P-Code interpreter.
P-Code is a tokenized concept where a command like "get value of sensor 2"
would simply become two bytes of data, e.g., 0x23 0x02 (not real values!).
This saves a LOT of space for the end program, and obviously reduces the
time required to send the program to the module.
But... :)
There's an engine running in the RCX that's reading through the data a byte
at a time and interpreting it all. So, it reads the "0x23" and knows it's a
command to read a sensor, then it reads the next byte "0x02" and knows
that's the sensor to read.
Then it executes the actual routine to read the sensor, and places the
result somewhere in memory or on the stack.
When you create NQC code, you're actually compiling code to it's native
form for the processor. So, the processor isn't running a software based
engine which is in turn reading your program data then working on it, the
processor is running your code directly.
The benefit of this is speed and cleaner access to all things in the RCX.
The downfall is that errant program code or data has the possibility of
crashing the RCX. As well, the program size is larger since you're
generating the machine code for the processor itself.
Hope that helps!
Mark
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Message has 1 Reply:
 | | RE: NQC versus Lego RCX Code Speed
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| (...) No, the Lego GUI software and NQC both produce code for the same target -- a simple interpreted virtual machine implemented in the firmware. I have never looked at the code produced by the Lego GUI, but I can't imagine it would be that much (...) (24 years ago, 5-Oct-00, to lugnet.robotics)
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