Kernel frequency setting?

[A_Camera]

not sure how you got 280 khz mathematically.

That's easy to answer...

Short circuit in my brains...

I calculated the frequency for 700mm/s speed, which is 280kHz.

If I would be right then I could not have 700mm/s2 acceleration. So yes, how did I get 280kHz... good question.

[Robertspark]

Oh, bit of a div!

400 steps per unit x 700 units / sec / sec = 280,000 steps /sec/sec.

I don't believe the acceleration profile works that way

[Robertspark]

I don't believe it works that way because the acceleration only takes place over the first 190mSec (0.19 Sec) after that the profile becomes linear.

I need to go and have a think however because it probably does depend on how linear you require the acceleration profile as there will not doubt be some rounding error at some point

[cncdrive]

The speed of an axis equals the step frequency.
The acceleration is the change in the step frequency.
In an acceleration phase the step frequency is growing until it reaches the target step frequency.
For example in an acceleration from 0 to x speed the frequency starts with 0 value and it reaches the x speed in some time.
The time it reaches the target frequency is the acceleration time.
In a decceleration phase the opposite happens, the axis runs with x speed and it reaches 0 in some time.

And the x target speed (target step frequency) can't be larger than the kernel frequency, because the kernel frequency is the upper limit of the setable speed (velocity), so you can't set a higher value than that.

I think from this explanation it is relatively simple to see that the step frequency never exceeds the kernel frequency in an acceleration or decceleraion phase.

Worst case theoritical scenarion is infinate acceleration, then in an acceleration phase the frequency changes from 0 Hz to x Hz in 0 time, it is a speed unit step.
The frequency still not exceeding x Hz, it just changes from 0 to x Hz in 0 time.