In SX Microcontrollers, SX/B Compiler and SX-Key Tool, George Herzog wrote:

Hi Bean,
Well, it is r/c PWM, which is roughly a 20 microsecond pulse, but wanders.  And the ON cycle is between 1 and 2 microseconds or according to Guenther's text it may only need to be between 1.3 and 1.7 microseconds.

From what I understand you don't need to measure the width of the whole pulse, merely the width of the on time.  How accurately?  Is 1% asking too much?  Obviously, the rougher the measurement, the easier it is to do, but I am unsure of how rough is useful.   1/256 of 2 microseconds would require one byte; 1/16th would require one nibble.  I suspect those the most convienent choices as I would be counting in a File Register.

I suppose that given those parameters, all I have to do is poll and increment the four inputs rather than actually to a capture/compare emulation.  As I understand it, the R/C reciever outputs the pulses in series [one after another] and if I know the sequence I can start with the #1 in an ISR and move immediately on to #2 after #1 shuts down.  [In otherwords, I do not have to seek information from all 4 in a random sequence or simultaneously].

Alternatively, I may be wrong and all the Pulses are arriving concurrently.  This would require a different strategy.

This is an old challange as I was trying to write an Assembly language equivalent of the SAMs Autopilot and the jump from C to Assembly for this is a bit unclear.

You discussion of Timers revived my interest.

Still I wonder if capture/compare happen to be something that Virtual Periphercal can or cannot do.

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