Unexpected results from Encoder::GetRate()

[jhersh]

Originally Posted by vamfun

Edit: Looking at the counter constructor for the quad encoder...seems that if
InitCounter(kExternalDirection);
is present then
SetDownSourceEdge(inverted, true);
has a special meaning. It sets direction externally with chan B rather than actually change the down count with chan B edges as the name implies. If this is the case, I really have the urge to yell at an overworked WPI programmer for this style of coding.

This is directly related to the register interface for the counter IP in the FPGA where bits that are not used in a given mode are overloaded to control other parts of the logic. The real failure here is that I didn't clearly document what wicked things I was doing with those bits in the library code.

Allow me to do that here...

If you select "ExternalDirection" mode, then the following overloads apply:
"DownRisingEdge" specifies invert the direction or not.
"DownFallingEdge => true" enables quadrature decoding mode.
In quadrature decoding mode, "UpFallingEdge" selects 1x or 2x decoding and "UpRisingEdge" must be true... more literally, what these two mean in quadrature mode is:
"UpRisingEdge => count A if B is high"
"UpFallingEdge => count A if B is low"

Obvious, right? Again sorry for the confusion (I realize you probably aren't any less confused at this point).

Originally Posted by vamfun

Also still waiting for Joe or other expert to explain how B channel works to set count direction in WPI libs .
post http://www.chiefdelphi.com/forums/sh...3&postcount=24

Here are the much anticipated logic equations used in the 1x and 2x quadrature decoding mode of the counters.

Count = (ARising | AFalling) & ((BHigh & UpRisingEdge) | (BLow & UpFallingEdge))
CountUp = Count & !(BHigh ^ DownRisingEdge ^ ARising)
CountDown = Count & (BHigh ^ DownRisingEdge ^ ARising)

With this, there will hopefully be no more mystery.

See you in Atlanta!
-Joe