Subject:
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Rotation sensor bug found (maybe!)
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Newsgroups:
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lugnet.robotics.rcx.legos
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Date:
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Sat, 17 Apr 1999 15:07:24 GMT
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Viewed:
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1339 times
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I think I might have found a bug in the ds_rotation_handler (direct-sensor.c).
The problem arises when the STATE_0_VALUE is checked using the IN_RANGE macro.
As STATE_0_VALUE is 1023U<<6, which is about the max value for an unsigned,
adding to it the RANGE_SIZE to test the upper bound gets an unwanted result.
The value would be over the max possible unsigned value and the result of the
addition is 40U<<6 - 1.
This is one of the points:
case STATE_1:
if ( IN_RANGE ( STATE_0_VALUE ) ) { <-- bug in this line
state=STATE_0;
cooked--;
} else if( IN_RANGE ( STATE_2_VALUE ) ) {
state=STATE_2;
cooked++;
}
break;
Second problem. I checked many values for my two rotation sensors, and as I
wrote yesterday they are different from the ones inside direct-sensor.c. In
some cases they are out of the range specified in legOS.
State Min value Max value Avg legOS value +/- range
0 65470 65470 65470 1023<<6 +/- 40<<6 = 65472 +/- 2560
1 54520 55230 54875 833<<6 +/- 40<<6 = 53312 +/- 2560
2 27960 28860 28410 405<<6 +/- 40<<6 = 25920 +/- 2560 !!!
3 41600 42560 42080 623<<6 +/- 40<<6 = 39872 +/- 2560 !!!
I didn't receive any comment about this problem up to now. Please somebody with
better knowledge of C and legOS confirm if I am right or wrong.
Thanks
Mario
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Message has 1 Reply:
 | | Re: Rotation sensor bug found (maybe!)
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| (...) You've got a point here. What if we hardwire STATE_0_VALUE to the following? #define STATE_0_VALUE (ds_unscale(1023U)-RANGE_SIZE) Or, for a more general approach: #define MIN(a,b) (a<b?a:b) #define MAX(a,b) (a>b?a:b) #define STATE_VALUE(k) ( \ (...) (26 years ago, 17-Apr-99, to lugnet.robotics.rcx.legos)
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