Subject:
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Re: SPIRIT SetSensorMode "slope" parameter
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Newsgroups:
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lugnet.robotics
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Date:
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Wed, 9 Dec 1998 19:30:17 GMT
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Viewed:
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963 times
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Laurentino Martins <lego-robotics@crynwr.com> wrote:
> I'm sure that the best persons to decode the use of that function are
> the guys that disassembled the firmware...
This is buried in the ROM, not the firmware. In particular, it is buried
in 14c0, byte read_sensor (short code, sensorstruct *sensor).
I didn't bother to decode this function in detail since most of its
functionality can be inferred from the function that calls it. However,
I'm almost positive that the code to deal with the sensor slope is in that
function.
Well, from looking briefly at that function, my hunch is now that it
operates off raw differences between successive values, i.e. a slope of x
sets up 1 transitions for +x changes in raw value, and 0 transitions for -x
changes in raw value. This is more specific than what I stated previously,
since it appears that the constant of proportionality has now been
determined; that constant is 1. Which means it works exactly like the
original poster thought it was supposed to, even though he seemed to
indicate he didn't observe it working that way.
Certainly I observed transitions due to changes in the raw value
proportional to the slope; that the constant of proportionality looks to be
1 does not surprise me, nor does it contradict what I remember observing
when I first took a look at this.
I should say that just now I didn't look at the 14c0 function too closely,
so I might have missed a scaling factor somewhere. And I vaguely remember
there being a reason for me not specifying the proportionality constant
when I first wrote up the documentation for set_sensor_mode; it might have
been because I didn't want to sit there and devise an experiment to figure
it out, it might have been that the constant didn't seem to be the obvious
choice, 1. So I definitely have to take a closer look at this sometime.
I'm hoping to get a chance to finish decoding the few remaining parts of
the ROM image and write up a ROM image spec sometime toward the end of this
month. I will go over 14c0 in detail then.
-Kekoa
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