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This library uses bit banging to control the LED strip. Because the mbed platform doesn't have a timer standardized that doesn't have a resolution lower a microsecond, we have to use NOPs. Also, the time it takes to toggle a GPIO pin is not consistent across platforms and it does not correlate to the system clock in any way. It is completely dependent on the platform's implementation.
For that reason, the only way to determine the timings for this library is to use a logic analyzer.
Above is a screenshot from a Saleae logic analyzer. You'll notice that the '1' pulse is longer than the '0' pulse and that the 'Latch' pulses are very similar. The timing requirements for these pulses can be found below (Source: http://wp.josh.com/2014/05/13/ws2812-neopixels-are-not-so-finicky-once-you-get-to-know-them/).
References:
WS2812B Datasheet: https://www.adafruit.com/datasheets/WS2812B.pdf
Overview of Timing: http://wp.josh.com/2014/05/13/ws2812-neopixels-are-not-so-finicky-once-you-get-to-know-them/