M73 support?  

// PRUSA CODES
// P F - Returns FW versions
// P R - Returns revision of printer

// G0 -> G1
// G1 - Coordinated Movement X Y Z E
// G2 - CW ARC
// G3 - CCW ARC
// G4 - Dwell S<seconds> or P<milliseconds>
// G10 - retract filament according to settings of M207
// G11 - retract recover filament according to settings of M208
// G28 - Home all Axis
// G29 - Detailed Z-Probe, probes the bed at 3 or more points. Will fail if you haven't homed yet.
// G30 - Single Z Probe, probes bed at current XY location.
// G31 - Dock sled (Z_PROBE_SLED only)
// G32 - Undock sled (Z_PROBE_SLED only)
// G80 - Automatic mesh bed leveling
// G81 - Print bed profile
// G90 - Use Absolute Coordinates
// G91 - Use Relative Coordinates
// G92 - Set current position to coordinates given

// M Codes
// M0 - Unconditional stop - Wait for user to press a button on the LCD (Only if ULTRA_LCD is enabled)
// M1 - Same as M0
// M17 - Enable/Power all stepper motors
// M18 - Disable all stepper motors; same as M84
// M20 - List SD card
// M21 - Init SD card
// M22 - Release SD card
// M23 - Select SD file (M23 filename.g)
// M24 - Start/resume SD print
// M25 - Pause SD print
// M26 - Set SD position in bytes (M26 S12345)
// M27 - Report SD print status
// M28 - Start SD write (M28 filename.g)
// M29 - Stop SD write
// M30 - Delete file from SD (M30 filename.g)
// M31 - Output time since last M109 or SD card start to serial
// M32 - Select file and start SD print (Can be used _while_ printing from SD card files):
// syntax "M32 /path/filename#", or "M32 S<startpos bytes> !filename#"
// Call gcode file : "M32 P !filename#" and return to caller file after finishing (similar to #include).
// The '#' is necessary when calling from within sd files, as it stops buffer prereading
// M42 - Change pin status via gcode Use M42 Px Sy to set pin x to value y, when omitting Px the onboard led will be used.
// M80 - Turn on Power Supply
// M81 - Turn off Power Supply
// M82 - Set E codes absolute (default)
// M83 - Set E codes relative while in Absolute Coordinates (G90) mode
// M84 - Disable steppers until next move,
// or use S<seconds> to specify an inactivity timeout, after which the steppers will be disabled. S0 to disable the timeout.
// M85 - Set inactivity shutdown timer with parameter S<seconds>. To disable set zero (default)
// M92 - Set axis_steps_per_unit - same syntax as G92
// M104 - Set extruder target temp
// M105 - Read current temp
// M106 - Fan on
// M107 - Fan off
// M109 - Sxxx Wait for extruder current temp to reach target temp. Waits only when heating
// Rxxx Wait for extruder current temp to reach target temp. Waits when heating and cooling
// IF AUTOTEMP is enabled, S<mintemp> B<maxtemp> F<factor>. Exit autotemp by any M109 without F
// M112 - Emergency stop
// M113 - Get or set the timeout interval for Host Keepalive "busy" messages
// M114 - Output current position to serial port
// M115 - Capabilities string
// M117 - display message
// M119 - Output Endstop status to serial port
// M126 - Solenoid Air Valve Open (BariCUDA support by jmil)
// M127 - Solenoid Air Valve Closed (BariCUDA vent to atmospheric pressure by jmil)
// M128 - EtoP Open (BariCUDA EtoP = electricity to air pressure transducer by jmil)
// M129 - EtoP Closed (BariCUDA EtoP = electricity to air pressure transducer by jmil)
// M140 - Set bed target temp
// M150 - Set BlinkM Color Output R: Red<0-255> U(!): Green<0-255> B: Blue<0-255> over i2c, G for green does not work.
// M190 - Sxxx Wait for bed current temp to reach target temp. Waits only when heating
// Rxxx Wait for bed current temp to reach target temp. Waits when heating and cooling
// M200 D<millimeters>- set filament diameter and set E axis units to cubic millimeters (use S0 to set back to millimeters).
// M201 - Set max acceleration in units/s^2 for print moves (M201 X1000 Y1000)
// M202 - Set max acceleration in units/s^2 for travel moves (M202 X1000 Y1000) Unused in Marlin!!
// M203 - Set maximum feedrate that your machine can sustain (M203 X200 Y200 Z300 E10000) in mm/sec
// M204 - Set default acceleration: S normal moves T filament only moves (M204 S3000 T7000) in mm/sec^2 also sets minimum segment time in ms (B20000) to prevent buffer under-runs and M20 minimum feedrate
// M205 - advanced settings: minimum travel speed S=while printing T=travel only, B=minimum segment time X= maximum xy jerk, Z=maximum Z jerk, E=maximum E jerk
// M206 - set additional homing offset
// M207 - set retract length S[positive mm] F[feedrate mm/min] Z[additional zlift/hop], stays in mm regardless of M200 setting
// M208 - set recover=unretract length S[positive mm surplus to the M207 S*] F[feedrate mm/sec]
// M209 - S<1=true/0=false> enable automatic retract detect if the slicer did not support G10/11: every normal extrude-only move will be classified as retract depending on the direction.
// M218 - set hotend offset (in mm): T<extruder_number> X<offset_on_X> Y<offset_on_Y>
// M220 S<factor in percent>- set speed factor override percentage
// M221 S<factor in percent>- set extrude factor override percentage
// M226 P<pin number> S<pin state>- Wait until the specified pin reaches the state required
// M240 - Trigger a camera to take a photograph
// M250 - Set LCD contrast C<contrast value> (value 0..63)
// M280 - set servo position absolute. P: servo index, S: angle or microseconds
// M300 - Play beep sound S<frequency Hz> P<duration ms>
// M301 - Set PID parameters P I and D
// M302 - Allow cold extrudes, or set the minimum extrude S<temperature>.
// M303 - PID relay autotune S<temperature> sets the target temperature. (default target temperature = 150C)
// M304 - Set bed PID parameters P I and D
// M400 - Finish all moves
// M401 - Lower z-probe if present
// M402 - Raise z-probe if present
// M404 - N<dia in mm> Enter the nominal filament width (3mm, 1.75mm ) or will display nominal filament width without parameters
// M405 - Turn on Filament Sensor extrusion control. Optional D<delay in cm> to set delay in centimeters between sensor and extruder
// M406 - Turn off Filament Sensor extrusion control
// M407 - Displays measured filament diameter
// M500 - stores parameters in EEPROM
// M501 - reads parameters from EEPROM (if you need reset them after you changed them temporarily).
// M502 - reverts to the default "factory settings". You still need to store them in EEPROM afterwards if you want to.
// M503 - print the current settings (from memory not from EEPROM)
// M509 - force language selection on next restart
// M540 - Use S[0|1] to enable or disable the stop SD card print on endstop hit (requires ABORT_ON_ENDSTOP_HIT_FEATURE_ENABLED)
// M600 - Pause for filament change X[pos] Y[pos] Z[relative lift] E[initial retract] L[later retract distance for removal]
// M605 - Set dual x-carriage movement mode: S<mode> [ X<duplication x-offset> R<duplication temp offset> ]
// M900 - Set LIN_ADVANCE options, if enabled. See Configuration_adv.h for details.
// M907 - Set digital trimpot motor current using axis codes.
// M908 - Control digital trimpot directly.
// M350 - Set microstepping mode.
// M351 - Toggle MS1 MS2 pins directly.