Issue with global variable while making 32-bit counter

Question

I am trying to do quadrature decoding using atmel xmega avr microcontroller. Xmega has only 16-bit counters. And in addition I hav

Answer 1

This problem is indeed a very common and very hard one. All solutions will toit will have a caveat regarding timing constraints in the lower priority layers. To clarify this: the highest priority function in your system is the hardware counter - it's response time defines the maximum frequency that you can eventually sample. The next lower priority in your solution is the interrupt routine which tries to keep track of bit 2^16 and the lowest is your application level code which tries to read the 32-bit value. The question now is, if you can quantify the shortest time between two level changes on the A- and B- inputs of your encoder. The shortest time usually does occur not at the highest speed that your real world axis is rotating but when halting at a position: through minimal vibrations the encoder can double swing between two increments, thereby producing e.g. a falling and a rising edge on the same encoder output in short succession. Iff (if and only if) you can guarantee that your interrupt processing time is shorter (by a margin) than this minmal time you can use such a method to virtually extend the coordinate range of your encoder.