Driver speed

[IhorNehrutsa]

BIGTREETECH declared the Product Parameters as:

Maximum speed: 1000RPM (revolutions per minute) 
Subdivision: 2 4 8 16 32

Stepper motor specifications is:

200 full steps per revolution (1.8° per step)

1000RPM is 1000/60 = 16.6666666667RPS (revolutions per second)
When 32 Subdivision is used than MAX frequency of input STEP pulses must be:
16.7 * 200 * 32 = 106880 Hz

I has tested frequency of input STEP pulses with original BIGTREETECH firmware.
It is near 50kHz.

I try to check MAX frequency of input STEP pulses in dev branch.
I use red LED to see duty cycle of motor step
Intellistep\src\hardware\timers.cpp:

// Just a simple stepping function. Interrupt functions can't be instance methods
void stepMotor() {
    digitalWriteFast(LED_PIN, HIGH);
    motor.step();
    digitalWriteFast(LED_PIN, LOW);
}

4kHz input STEP pulses:

red LED

5kHz input STEP pulses:

red LED

There is no more time to process input STEP pulses.
We need faster algorithms.

[CAP1Sup]

@IhorNehrutsa thanks for doing the testing! Unfortunately, I don't have the equipment to do that kind of testing, so it's great to see how everything is working. Do you have any ideas on how we can speed up the stepping routine?

[CAP1Sup]

Did you disable all of the closed loop interrupts and everything? That could be really hurting the performance

[CAP1Sup]

@IhorNehrutsa since you have an oscilloscope, would it be possible for you to test the frequency of the oscillator on the board? I was unable to find a solid value that was actually accurate for the external (HSE), so I was forced to use the internal oscillator (HSI). The thing is, when you use the internal, it forces you to cut the frequency down by half. This leads to longer compute times and slower overall performance. I think that we could get around 2x more performance by just figuring out that value.

Note: the pin you need is the 5th pin on the left of you have the dot in the top left. That is where the HSE input signal enters the STM32

[IhorNehrutsa]

HSI and PLL allow to set 64MHz SYSCLK. See STM32Cube

I measured HSE oscillator. It is 8MHz.

[IhorNehrutsa]

Did you disable all of the closed loop interrupts and everything? That could be really hurting the performance

Yes, I switch off correctionTimer in timers.cpp

[CAP1Sup]

@IhorNehrutsa how are we doing on max update rate now? I'm thinking that it should be higher

[IhorNehrutsa]

I will mesute it tomorrow in office.
My time zone is UTC+3.

[IhorNehrutsa]

Not as I expected.
It's still 30kHz.
WIP

[IhorNehrutsa]

with merged
https://github.com/CAP1Sup/Intellistep/tree/Stepping-Speed-Improvements
47kHz
WIP

[IhorNehrutsa]

Measured on master branch
c014991
48.3kHz

#50
SINE_MAX a power of 2 to fast division to SINE_MAX
49.3kHz

[CAP1Sup]

Truly a massive performance gain. Thanks so much Ihor. It was a great help! Can I close this now? I think we meet BTT's performance at this point

[IhorNehrutsa]

1000RPM is 1000/60 = 16.6666666667RPS (revolutions per second)
When 32 Subdivision is used than MAX frequency of input STEP pulses must be:
16.7 * 200 * 32 = 106880 Hz
16.7 * 200 * 16 = 53440 Hz
16.7 * 200 * 8 = 26720 Hz

It is too early, 16 and 32 step subdivisions are still unachievable. :(

[CAP1Sup]

If I do the calculations the other way, the maximum rate is 7.7 rps at 1/32 microstepping. Now, if you consider that a typical printer pulley is about 10 mm to 15mm in diameter, that would lead to a maximum linear speed of 242 mm/s and 363 mm/s respectively. I really don't think that people are going to be exceeding that. Also, I don't think that there's much more performance to be had unfortunately. Maybe some minor gains, but I don't think that we'll double our current rate

[IhorNehrutsa]

My target project is not a 3D printer. It is a high-speed tracking/positioning system.
1/8 step is too loud and twitchy.

[IhorNehrutsa]

How to force the compiler to save preprocessed files?
I can't find it.
Thanks.