Marlin

Contents

Quick Information

This RepRap firmware is a mashup between Sprinter, Grbl and many original parts.

Derived from Sprinter and Grbl by Erik van der Zalm. Sprinter's lead developers are Kliment and caru. Grbl's lead developer is Simen Svale Skogsrud. Sonney Jeon (Chamnit) improved some parts of Grbl. A fork by bkubicek for the Ultimaker was merged, and further development was aided by him. Some features have been added by: Lampmaker, Bradley Feldman, and others.

Features:

• Interrupt based movement with real linear acceleration.
• High steprate.
• Look ahead (Keep the speed high when possible. High cornering speed).
• Interrupt based temperature protection.
• preliminary support for Matthew Roberts advance algorithm For more info see: http://reprap.org/pipermail/reprap-dev/2011-May/003323.html .
• Full endstop support.
• SD Card support.
• SD Card folders (works in Pronterface).
• LCD support (ideally 20x4 or 128x64).
• LCD menu system for autonomous SD card printing, controlled by an click-encoder.
• EEPROM storage of e.g. max-velocity, max-acceleration, and similar variables.
• many small but handy things originating from bkubicek's fork.
• Arc support.
• Temperature oversampling.
• Dynamic Temperature setpointing aka "AutoTemp".
• Support for QTMarlin, a very beta GUI for PID-tuning and velocity-acceleration testing. https://github.com/bkubicek/QTMarlin
• Endstop trigger reporting to the host software.
• Updated sdcardlib.
• Heater power reporting. Useful for PID monitoring.
• CoreXY kinematics (http://www.corexy.com/theory.html ).
• Delta kinematics.
• SCARA kinematics.
• Auto bed leveling (actually auto bed compensation) support has been added.
• Firmware binary size between around 50kB and 100kB, depending on options.

The default baudrate is 250000. Because this baudrate is directly derived from the usual 16MHz clock of the Arduino MCU, it has less jitter and hence errors than the usual 115200 baud, but 250000 baud is less supported by drivers and host-environments.

Differences from and additions to the already good Sprinter firmware

Look-ahead

Marlin has jerk-type look-ahead. Whithout it, it would brake to a stop and re-accelerate at each corner. Lookahead will only decelerate and accelerate to some non-zero velocity, so that the change in vectorial velocity magnitude is less than the xy_jerk_velocity. This is only possible, if some future moves are already processed, hence the name look-ahead. It leads to less over-deposition of material at corners, especially at flat angles.

Slic3r can find curves that, although broken into segments, were meant to describe an arc. Marlin is able to print those arcs. The advantage is that the firmware can choose the resolution, and can perform the arc with nearly constant velocity, resulting in a nice finish. Also, less serial communication is needed.

To reduce noise and make the PID-differential term more useful, 16 ADC conversion results are averaged.

If your gcode contains a wide spread of extruder velocities, or you realtime change the building speed, the temperature should be changed accordingly. Usually, higher speed requires higher temperature. This can now be performed by the AutoTemp function. Enable AutoTemp mode with M109 S T F and disable it with M109 (without any F value). When active, the maximal extruder stepper rate of all buffered moves is calculated and named "maxerate" [steps/sec]. The desired temperature is then set to t=tempmin+factor*maxerate, constrained between tempmin and tempmax. If the target temperature is set manually or by GCode to a value less then tempmin, it will be kept without change. Ideally, your GCode can be completely free of temperature controls, apart from a M109 S T F in the start.gcode, and a M109 S0 in the end.gcode.

If you have established known working PID constants, acceleration, and max-velocity settings for your own machine, you can set them, then store them in the EEPROM. On each boot-up, Marlin will automatically load these values from EEPROM, independent of what your compiled Configuration.h says.

If your hardware supports it, you can build a LCD-CardReader+Click+encoder combination. This will allow you to adjust temperatures, accelerations, velocities, and flow rates in realtime (while printing). It also provides the ability to select and print files directly from the SD card, preheat the extruder, disable the stepper motors, and do other interesting things. One working hardware configuration is documented here: http://www.thingiverse.com/thing:12663. If you have at least a 20x4 or 16x2 display, useful data is shown.

If you have an SD card reader attached to your controller, folders are supported to a depth of 10 levels. Listing files in Pronterface shows "/path/subpath/file.g". You can write to files in subfolders by including the path (in lowercase). (Hidden files, backup files, and non-GCode files are not included in file listings.)

Endstop trigger reporting

If an endstop is hit while moving towards the endstop, the location at which the firmware thinks the endstop was triggered is output to the serial port. This is useful because the user gets a warning message. Tools like QTMarlin can use this to find acceptable combinations of velocity+acceleration.

Coding paradigm

Not relevant from the user perspective, but Marlin is split into thematic chunks, and has tried to partially enforce private variables. This is intended to make interactions between modules clearer, and leads to a higher level of encapsulation. We think this will be useful as a preliminary step for porting to other platforms, such as ARM. Lots of RAM (with enabled LCD

2200 bytes) was saved by storing character strings in Program Memory. In the serial communication, a #define-based level of abstraction was enforced, so transfer of information is clear (usually beginning with "echo:"), an error "error:", or just normal protocol, necessary for backwards compatibility.

Interrupt based temperature measurements

An interrupt is used to manage ADC conversions, and enforce checking for critical temperatures. This leads to less blocking in the heater management routine.