[Configuration/LCD] Add standalone configuration defaults and LCD menu controls for Non-Linear Extrusion parameters (A, B, and C)

[fanXbox]

Is your feature request related to a problem? Please describe.

Currently, when a user enables NONLINEAR_EXTRUSION in Configuration_adv.h, the sub-option NONLINEAR_EXTRUSION_DEFAULT_ON is commented out by default. This forces users to manually turn on the feature via G-code or LCD and save it to EEPROM after every firmware flash or EEPROM reset.

Additionally, the advanced LCD menu only allows toggling the feature on or off, but completely lacks any interface to view, tune, or adjust the individual parameters (Coefficients A, B, and Limit C) directly from the printer. This creates a significant friction point for standalone adjustments.

Are you looking for hardware support?

No response

Describe the feature you want

I propose to improve the Non-Linear Extrusion standalone user experience through two changes:

1. Configuration Defaults (Marlin/Configuration_adv.h)

Uncomment NONLINEAR_EXTRUSION_DEFAULT_ON by default inside the existing #if ENABLED(NONLINEAR_EXTRUSION) block. Since it is already safely wrapped inside the parent condition, users who explicitly enable the feature should naturally expect it to be active upon booting without extra manual steps.
Currently, leaving it commented out forces users to manually reactivate the feature via G-code (M592 S1) or via the LCD menu and save it to EEPROM after every firmware flash or EEPROM reset (M502).

For reference, the parameter structure is defined as follows in the header comment of Marlin/src/gcode/feature/nonlinear/M592.cpp:

• M592: Get or set nonlinear extrusion parameters
• S Enable / Disable Nonlinear Extrusion
• A Quadratic coefficient (default 0.0)
• B Linear coefficient (default 0.0)
• C Constant coefficient (default 1.0)

2. LCD Menu Interface (Marlin/src/lcd/menu/menu_advanced.cpp)

Expand the advanced settings menu to include input fields for the individual parameters.
To ensure proper tuning capability, Coefficients A and B require high precision, while Limit C only needs standard precision.

Replace:

#if ENABLED(NONLINEAR_EXTRUSION)
  EDIT_ITEM(bool, MSG_NLE_ON, &stepper.ne.settings.enabled);
#endif

With:

#if ENABLED(NONLINEAR_EXTRUSION)
  EDIT_ITEM(bool, MSG_NLE_ON, &stepper.ne.settings.enabled);
  EDIT_ITEM_FAST(float54, MSG_NLE_A, &stepper.ne.settings.coeff.A, 0.0f, 1.0f); // 4 decimals for micro-adjustments
  EDIT_ITEM_FAST(float54, MSG_NLE_B, &stepper.ne.settings.coeff.B, 0.0f, 1.0f); // 4 decimals for micro-adjustments
  EDIT_ITEM_FAST(float32, MSG_NLE_C, &stepper.ne.settings.coeff.C, 0.0f, 2.0f); // 2 decimals for standard limits
#endif

3. Language Definitions (Marlin/src/lcd/language/language_en.h)

Add the missing English language string definitions right after MSG_NLE_ON:

  LSTR MSG_NLE_A                          = _UxGT("NLE Quadratic");
  LSTR MSG_NLE_B                          = _UxGT("NLE Linear");
  LSTR MSG_NLE_C                          = _UxGT("NLE Constant");

Note on Constant (C):
While adding the Quadratic (A) and Linear (B) menu items is essential for proper tuning, the Constant (C) coefficient is rarely changed from its default value of 1.0. Therefore, if the community prefers to keep the LCD menu more compact, the Constant (C) item can be omitted, as tuning A and B alone satisfies almost all real-world calibration needs.

Additional context

This complete implementation provides true standalone capability for Non-Linear Extrusion. It streamlines the calibration process for advanced users, prevents accidental extrusion issues if the EEPROM is wiped during a firmware update, and makes the feature significantly more accessible.

[fanXbox]

Feature Enhancement Proposal & Technical Details: Pre-set Nonlinear Factors

I have successfully identified, implemented, and validated a clean solution to allow pre-setting the nonlinear parameters A, B, and C directly within the firmware configuration files.

Why this is useful (Benefits)

• For Printer Manufacturers: Allows shipping machines with custom calibrated default values pre-configured out of the box.
• For Modders & Advanced Users: Facilitates flashing firmware with custom defaults, ensuring these parameters are safely retained even after an EEPROM reset (M502).
• Perfect Synergy with the Proposed LCD Menu: This configuration layer complements the LCD menu modification I proposed in my initial post. It ensures that the display menu will load these custom firmware defaults as its starting values, while still allowing users to adjust them manually via the screen at any time.

---

Code Implementation

To implement this, two files need to be modified. The code includes safe fallbacks to ensure compatibility with older configuration files.

1. In Marlin/Configuration_adv.h

Under the NONLINEAR_EXTRUSION section, update the block to include the new default factor definitions:

Replace this:

#if ENABLED(NONLINEAR_EXTRUSION)
  #define NONLINEAR_EXTRUSION_DEFAULT_ON    // Enable if NLE should be ON by default
#endif

With this:

#if ENABLED(NONLINEAR_EXTRUSION)
  #define NONLINEAR_EXTRUSION_DEFAULT_ON    // Enable if NLE should be ON by default
  #define NONLINEAR_FACTOR_A 0.0000       // Quadratic coefficient (default 0.0)
  #define NONLINEAR_FACTOR_B 0.0000       // Linear coefficient (default 0.0)
  #define NONLINEAR_FACTOR_C 1.00         // Constant coefficient (default 1.0)
#endif

2. In Marlin/src/module/stepper.h

Replace the hardcoded initialization line to read the configuration macros if defined, or fall back to original defaults:

Replace this:

{ A = B = 0.0f; C = 1.0f; }

With this:

{
  A = #ifdef NONLINEAR_FACTOR_A ? NONLINEAR_FACTOR_A : 0.0f;
  B = #ifdef NONLINEAR_FACTOR_B ? NONLINEAR_FACTOR_B : 0.0f;
  C = #ifdef NONLINEAR_FACTOR_C ? NONLINEAR_FACTOR_C : 1.0f;
}

I would love to see this integrated into the official Marlin repository to improve flexibility for the community.