Linear Advance Messages

I've just recently upgraded my Marlin Firmware to 2.1.x from 2.0.x and I'm trying to turn on Linear Advance again. I've got it on successfully and determined the K value based on the test print, but when I print some other object, I'm getting flooded with the messages "Acceleration Limited" and "eISR running at > 10kHz".

I want to understand what the issues are and if this means that Linear Advance is not actually being used. I know the Acceleration limited is related to my acceleration settings, but which ones and what should I try to reduce or get rid of those messages?

I've set all my default feed rates and acceleration values to the defaults from the example Configuration.h. I'm using Junction Deviation with a value of 0.13, and not using S Curve. My board is a BTT SKR 1.4 Turbo. I'm using an E3Dv2 with a Titan extruder (not bowden) Here are some of the pertinent settings from my config files:

#define DEFAULT_MAX_FEEDRATE          { 300, 300, 6, 25 }

//#define LIMITED_MAX_FR_EDITING        // Limit edit via M203 or LCD to DEFAULT_MAX_FEEDRATE * 2
#if ENABLED(LIMITED_MAX_FR_EDITING)
  #define MAX_FEEDRATE_EDIT_VALUES    { 600, 600, 10, 50 } // ...or, set your own edit limits
#endif

/**
 * Default Max Acceleration (speed change with time) (linear=mm/(s^2), rotational=°/(s^2))
 * (Maximum start speed for accelerated moves)
 * Override with M201
 *                                      X, Y, Z [, I [, J [, K...]]], E0 [, E1[, E2...]]
 */
#define DEFAULT_MAX_ACCELERATION      { 3000, 3000, 100, 10000 }

//#define LIMITED_MAX_ACCEL_EDITING     // Limit edit via M201 or LCD to DEFAULT_MAX_ACCELERATION * 2
#if ENABLED(LIMITED_MAX_ACCEL_EDITING)
  #define MAX_ACCEL_EDIT_VALUES       { 6000, 6000, 200, 20000 } // ...or, set your own edit limits
#endif

/**
 * Default Acceleration (speed change with time) (linear=mm/(s^2), rotational=°/(s^2))
 * Override with M204
 *
 *   M204 P    Acceleration
 *   M204 R    Retract Acceleration
 *   M204 T    Travel Acceleration
 */
#define DEFAULT_ACCELERATION          1800    // X, Y, Z and E acceleration for printing moves
#define DEFAULT_RETRACT_ACCELERATION  3000    // E acceleration for retracts
#define DEFAULT_TRAVEL_ACCELERATION   1500    // X, Y, Z acceleration for travel (non printing) moves

/**
 * Default Jerk limits (mm/s)
 * Override with M205 X Y Z . . . E
 *
 * "Jerk" specifies the minimum speed change that requires acceleration.
 * When changing speed and direction, if the difference is less than the
 * value set here, it may happen instantaneously.
 */
//#define CLASSIC_JERK
#if ENABLED(CLASSIC_JERK)
  #define DEFAULT_XJERK 4.5
  #define DEFAULT_YJERK 4.5
  #define DEFAULT_ZJERK  0.4
  //#define DEFAULT_XJERK 10.0
  //#define DEFAULT_YJERK 10.0
  //#define DEFAULT_ZJERK  0.3
  //#define DEFAULT_IJERK  0.3
  //#define DEFAULT_JJERK  0.3
  //#define DEFAULT_KJERK  0.3

  //#define TRAVEL_EXTRA_XYJERK 0.0     // Additional jerk allowance for all travel moves

  //#define LIMITED_JERK_EDITING        // Limit edit via M205 or LCD to DEFAULT_aJERK * 2
  #if ENABLED(LIMITED_JERK_EDITING)
    #define MAX_JERK_EDIT_VALUES { 20, 20, 0.6, 10 } // ...or, set your own edit limits
  #endif
#endif

#define DEFAULT_EJERK    5.0  // May be used by Linear Advance

you DEFAULT_MAX_ACCELERATION e value is silly high

You can look in Marlin's E3 V2 example configurations to see what the usual settings are.

I don't think the "eISR running at > 10kHz" is an issue. 8 bit systems would be struggling but your system is using a 32 bit LPC1768 so it shouldn't be a problem.

"Acceleration Limited" is concerning. It is looking at the E jerk settings, the MIN_STEPS_PER_SEGMENT setting, K value and retract length. The retract length can be set in either the slicer or over ridden by configuration_adv.h settings. Double check that these settings are reasonable.

Here is the comment in the "Acceleration Limited" code.
// Check for unusual high e_D ratio to detect if a retract move was combined with the last print move due to min. steps per segment. Never execute this with advance!
// This assumes no one will use a retract length of 0mm < retr_length < ~0.2mm and no one will print 100mm wide lines using 3mm filament or 35mm wide lines using 1.75mm filament.

The "Acceleration Limited" message can be disabled by commenting out LA_DEBUG in configuration_adv.h.

When CLASSIC_JERK is disabled, DEFAULT_EJERK is used by Linear Advance. You may want to try enabling CLASSIC_JERK, re-running the Linera Advance test suite, setting the new K and then seeing if the prints are any better.

I didn't think to look at the examples folder for the configurations. I took the default values from the Marlin Configuration repo, but just used the ones from the release-2.1.2 branch.

My problem is I'm not sure which name brand printer mine could be similar to. My printer started out as a Prusa i3a clone about 9 years ago, but has since been redesigned and rebuilt and there's not one piece of the original printer left. It now uses OpenBuilds vslot and cbeam for the axes and has the e3dv2 hotend with a titan extruder. But it still is a cartesian printer and it has the 32-bit mainboard.

I'm mostly interested in the extruder default feed rates and acceleration values. Are there any of those name brand printers from the Marlin examples that ship with a Titan or Titan Aero e3dv6 combination?

I think you'll need to do some manual filament feeds to test the capabiliities of your system.

Send M201 Exxx to set the extruder acceleration to a low value. Try 250 as a starting point

Send M203 Exxx to set the extruder max feedrate to an insanely high value. Try 5000 as a starting point.

Send G1 E25 Fxxx commands and listen to the sounds the extruder makes. It should be smooth with no clicking/grinding. Increase the feedrate until the system complains. A max feedrate setting of about 2/3 of where it complains should be safe to use.

Send M201 Exxx to set the extruder acceleration to higher values and then send G1 E25 Fxxx commands with the feedate set to the 2/3 value. Eventually you'll hear the extruder complain. A max acceleration of about 2/3 should be safe to use.

You can also do the same with the X, Y and Z axis.

Actually, I know the max feed rate values and I've calibrated the extruder extensively and know its max feed rate as well. It's the acceleration and jerk values that are always a mystery.

I found some more reasonable settings in some of the example configs. I still get the output messages, but I'm not sure if I can actually get rid of them. My prints don't come out bad, but I've recently started printing my first roll of PETG after printing exclusively ABS for many years. I'm having tons of trouble with bridges and there are so many potential variables, I'm just trying to start from scratch and work on every aspect of the settings to try and get things working.

I'm going to be starting another thread to try and tackle issues as to why I need huge retraction values with a direct drive extruder.

Thanks for the help.