> The gyro puts out 38k4 data bursts at the rate of 75 - 77 bursts
> per second. The information in the data is converted to a number
> of pulses that are sent to motor drivers. Everything is working....
>
> .....except. The motors really perform best when supplied with
> evenly-spaced pulses. At present each motor is set to require
> 1200 pulses to move a gearbox 1 degree
>
> The problem is that the bursts (as measured from the end of the
> fifth byte in one to the end of the fifth byte in the next) are not evenly
> spread, and can be anywhere from 11 to 14ms apart.

This sounds to me like a filtering problem.  You have data coming in in
bursts, and need to send it out smoothly in time.

I'm not totally clear on this, but I guess each gyro burst indicates a
number of pulses that need to be sent to a motor over the next 11 to 14mS or
so.  Suppose the gyro burst only adds to a counter that keeps track of
pending pulses to be sent to the motor, and the counter is decremented for
every pulse sent.  Whenever a gyro burst comes in and the counter is
updated, calculate the new period between pulses so that the counter would
reach zero a bit after the latest time for the next gyro pulse, like 20mS
for example.

This would keep the pulses coming regularly, with a change in pulse period
after every gyro burst.  If you want to smooth that out too, just low pass
filter the pulse period a bit.  You get smooth operation at the cost of some
lag.  I can't tell if that's acceptable.

It seems the most time-critical thing you are doing is producing the regular
pulses.  I would therefore generate the pulses from an interrupt.  This
shouldn't take many cycles on the average, so there are plenty left for the
foreground loop to receive the gyro bursts, determine the number of
resulting motor pulses, update the pending pulses counter, and compute the
new pulse period.


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