For Beaglebone Black: A G-code interpreter and stepmotor controller for coordinated moves of up to 8 steppers. Uses the Programmable Realtime Unit (PRU).
C++ C Assembly Makefile Shell
Clone or download
bigguiness and hzeller gcode-machine-control: Allow G28 to be aborted by hardware E-Stop.
A G28 (goto limits) will block until all the requested limits have
been hit and backed-off. This can be a problem sometimes, specifically:

1) If an axis is wired backwards the limit will never be reached.
2) If a normally-open limit is disconnected it will never be detected.
3) If a mechanical issue prevents a limit from being reached.
4) If a G28 needs to be aborted for some other reason.

Modify move_to_endstop() so that the search/back-off will be aborted
if a hardware E-Stop is detected. Then check_for_estop() at the end
of go_home() to make sure that the homing_state_ is set correctly.

Signed-off-by: H Hartley Sweeten <>
Latest commit 4e3f93c Jul 27, 2018


Step-motor controller for CNC-like devices (or 3D printers) using the PRU (Programmable Realtime Unit) of the Beaglebone Black to create precisely timed and fast stepper-pulses for acceleration and travel. (And with fast, we're talking up to 1Mhz fast. For 8 motors in parallel. In a controlled move (G1). So this is not a limit in real-world applications).

Works with a cape designed by the author (the BUMPS cape), but also provides relatively easy adaption to new hardware (currently: support for CRAMPS). See hardware subdirectory.

This was one of my very early tests: First Test

The {accl-,decel-}eration and travel motion profile is entirely created within the PRU from parameters sent by the host CPU decoupled via a ring-buffer. The BeagleBone main CPU prepares the data, such as parsing the G-Code and doing travel planning, while all the real-time critical parts are done in the PRU. The host CPU typically needs less than 1% CPU-time doing everything else (and there is no need for a real-time kernel).

The main machine-control program is parsing G-Code, extracting axes moves and enqueues them to the realtime unit. It can receive G-Code from a file or socket (you can just telnet to it for an interactive session, how cool is that?).


For system configuration and building the machine-control binary, see

Getting started

Before you can use beagleg and get meaningful outputs on the GPIO pins, we have to tell the pin multiplexer to connect them to the output pins. For that, just run the script with your hardware to install the device overlay. You find it in the hardware/ subdirectory.

sudo hardware/ hardware/BUMPS/BeagleG.dts

See the Hardware page how to enable the cape at boot time. (Note: this section will be simpler once we switched entirely to universal cape).

Machine control binary

To control a machine with G-Code, use the machine-control binary. This either takes a filename or a TCP port to listen on.

Usage: ./machine-control [options] [<gcode-filename>]
  -c, --config <config-file> : Configuration file. (Required)
  -p, --port <port>          : Listen on this TCP port for GCode.
  -b, --bind-addr <bind-ip>  : Bind to this IP (Default:
  -l, --logfile <logfile>    : Logfile to use. If empty, messages go to syslog (Default: /dev/stderr).
      --param <paramfile>    : Parameter file to use.
  -d, --daemon               : Run as daemon.
      --priv <uid>[:<gid>]   : After opening GPIO: drop privileges to this (default: daemon:daemon)
      --help                 : Display this help text and exit.

Mostly for testing and debugging:
  -f <factor>                : Feedrate speed factor (Default 1.0).
  -n                         : Dryrun; don't send to motors, no GPIO or PRU needed (Default: off).
  -P                         : Verbose: Show some more debug output (Default: off).
  -S                         : Synchronous: don't queue (Default: off).
      --allow-m111           : Allow changing the debug level with M111 (Default: off).

Segment acceleration tuning:
     --threshold-angle       : Specifies the threshold angle used for segment acceleration (Default: 10 degrees).
     --speed-tune-angle      : Specifies the angle used for proportional speed-tuning. (Default: 60 degrees)

                               The --threshold-angle + --speed-tune-angle must be less than 90 degrees.

Configuration file overrides:
     --homing-required       : Require homing before any moves (require-homing = yes).
     --nohoming-required     : (Opposite of above^): Don't require homing before any moves (require-homing = no).
     --norange-check         : Disable machine limit checks. (range-check = no).

The axis configurations (max feedrate, acceleration, travel, motor mapping,...) is configured in a configuration file like in this example.

The G-Code understands logical axes X, Y, Z, E, A, B, C, U, V, and W.

More details about the G-Code code parsed and handled can be found in the G-Code documentation.


For testing your motor settings, you might initially just have a simple file:

sudo ./machine-control -c my.config -f 10 myfile.gcode

Output the file myfile.gcode in 10x the original speed (say you want to stress-test). Note, the factor will only scale feedrate, but the machine will always obey the machine constraints with maximum feed and acceleration given in the configuration file.

echo "G1 X100 F10000 G1 X0 F1000" | sudo ./machine-control /dev/stdin

This command directly executes some GCode coming from stdin. This is in particular useful when you're calibrating your machine and need to work on little tweaks.

sudo ./machine-control -c my.config --port 4444

Listen on TCP port 4444 for incoming connections and execute G-Codes over this line. So you could use telnet beaglebone-hostname 4444 to have an interactive session or send a file simple via socat from a remote machine:

 cat myfile.gcode | socat -t5 - TCP4:beaglebone-hostname:4444

Use socat, don't use the ancient nc (netcat) - its buffering seems to be broken so that it can get stuck. With socat, it should be possible to connect to a pseudo-terminal in case your printer-software only talks to a terminal (haven't tried that yet, please let me know if it works).

Note, there can only be one open TCP connection at any given time (after all, there is only one physical machine).

G-Code stats binary

There is a binary gcode-print-stats to extract information from the G-Code file e.g. accurate expected print-time, Object height (=maximum Z-axis), filament length. This is in particular useful because many GCode runtime estimators are widely off; this is accurate to the second because it takes all acceleration phases into account.

Usage: ./gcode-print-stats [options] <gcode-file> [<gcode-file> ..]
        -c <config>       : Machine config
        -f <factor>       : Speedup-factor for feedrate.
        -H                : Toggle print header line
Use filename '-' for stdin.

The output is in column form, so you can use standard tools to process them. For instance, from a bunch of gcode files, find the one that takes the longest time

./gcode-print-stats -c my.config *.gcode | sort -k2 -n


The BUMPS-cape is one of the capes to use, it was developed together with BeagleG (but it is not widely distributed yet). BeagleG also works with the CRAMPS board, which is a popular motor driver cape for the BeagleBone Black. You can easily adapt your own hardware, check the hardware sub-directory.

Bumps board

Axis to Motor mapping

Each board has a number of connectors for motors and switches to which you connect your physical motors and end-switches to.

To map these connector positions to logical axes names, the machine-control binary has a configuration file in which you can configure not only the various axis parameters (max speed, acceleration, steps/mm), but also assign these axes to motor drivers provided by the cape (motor_1, motor_2,...) and end switches (switch_1, switch_2,...) to logical functions (e.g. min_x). See the annotated config file.


If you want to use the nicely seprated sub-APIs of BeagleG programmatically or want to get involved in the development, check the Development page.


BeagleG is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.


Not everything I'd like to have is implemented yet, but getting closer as weekend hacking permits.

  • Needed for full 3D printer solution: add PWM/PID-loop for heaters.
  • Fast pause without waiting for queues to empty, but still be able to recover exact last position. That way pause/resume is possible.
  • ...