DigitalInstruments - external clock

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External clock will be handled by either manually setting external clock frequency, and scopy will assume this is the correct frequency/sample rate.

If external clock frequency is not set, logic instruments will use clks as unit of measurement instead of seconds.

For the pattern generator, a new set of patterns needs to be developed that are only activated when the frequency is not set. These implemented patterns will not be time dependent. These patterns include pulse generator,counters,random patterns, SPI, I2C.