Marlin——開源固件，3D打印控制系統。本質是一個Gcode代碼解釋器，接收來自上位機的控制命令或者讀取存儲卡中的gcode文件。把程序（固件）燒錄到主板，這塊主板就相當於微型電腦一般，而控制系統就相當於操作系統（這是我以前接觸這塊的理解）。研究Marlin代碼，我覺得最好是有一些電子方面的知識，容易理解（可惜我這方面知識很薄弱，只是略懂皮毛）。
控制系統，顧名思義，主要是用於控制主板各種行爲。
1.驅動控制板；
2.執行隊列中的命令；
3.控制步進電機；
4.溫度控制和偵測(擠出頭和熱牀的溫度)；
5.讀寫SD卡；
6.控制顯示屏（LCD或觸摸屏）
Configuration.h：主要是一些定義，如波特率，打印行程， 限位開關，PID等。ultralcd.h和ultralcd.cpp：顯示屏界面。watchdog.h和watchdog.cpp：看門狗。
Marlin_main.cpp：setup()函數用於初始化工作。
/*
* Marlin entry-point: Set up before the program loop
* - Set up the kill pin, filament runout, power hold
* - Start the serial port
* - Print startup messages and diagnostics
* - Get EEPROM or default settings
* - Initialize managers for:
* temperature
* planner
* watchdog
* stepper
* photo pin
* servos
* LCD controller
* Digipot I2C
* Z probe sled
* status LEDs
*/
loop()函數：重複執行。
/**
* The main Marlin program loop
*
* - Save or log commands to SD
* - Process available commands (if not saving)
* - Call heater manager
* - Call inactivity manager
* - Call endstop manager
* - Call LCD update
*/
相關指令：
/* "G" Codes
*
* G0 -> G1
* G1 - Coordinated Movement X Y Z E
* G2 - CW ARC
* G3 - CCW ARC
* G4 - Dwell S<seconds> or P<milliseconds>
* G5 - Cubic B-spline with XYZE destination and IJPQ offsets
* G10 - Retract filament according to settings of M207
* G11 - Retract recover filament according to settings of M208
* G12 - Clean tool
* G20 - Set input units to inches
* G21 - Set input units to millimeters
* G28 - Home one or more axes
* 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 X Y location (defaults to current XY location)
* G31 - Dock sled (Z_PROBE_SLED only)
* G32 - Undock sled (Z_PROBE_SLED only)
* G38 - Probe target - similar to G28 except it uses the Z_MIN endstop for all three axes
* 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. (Requires SDSUPPORT)
* M21 - Init SD card. (Requires SDSUPPORT)
* M22 - Release SD card. (Requires SDSUPPORT)
* M23 - Select SD file: "M23 /path/file.gco". (Requires SDSUPPORT)
* M24 - Start/resume SD print. (Requires SDSUPPORT)
* M25 - Pause SD print. (Requires SDSUPPORT)
* M26 - Set SD position in bytes: "M26 S12345". (Requires SDSUPPORT)
* M27 - Report SD print status. (Requires SDSUPPORT)
* M28 - Start SD write: "M28 /path/file.gco". (Requires SDSUPPORT)
* M29 - Stop SD write. (Requires SDSUPPORT)
* M30 - Delete file from SD: "M30 /path/file.gco"
* M31 - Report time since last M109 or SD card start to serial.
* M32 - Select file and start SD print: "M32 [S<bytepos>] !/path/file.gco#". (Requires SDSUPPORT)
* Use P to run other files as sub-programs: "M32 P !filename#"
* The '#' is necessary when calling from within sd files, as it stops buffer prereading
* M33 - Get the longname version of a path. (Requires LONG_FILENAME_HOST_SUPPORT)
* M42 - Change pin status via gcode: M42 P<pin> S<value>. LED pin assumed if P is omitted.
* M43 - Monitor pins & report changes - report active pins
* M48 - Measure Z Probe repeatability: M48 P<points> X<pos> Y<pos> V<level> E<engage> L<legs>. (Requires Z_MIN_PROBE_REPEATABILITY_TEST)
* M75 - Start the print job timer.
* M76 - Pause the print job timer.
* M77 - Stop the print job timer.
* M78 - Show statistical information about the print jobs. (Requires PRINTCOUNTER)
* M80 - Turn on Power Supply. (Requires POWER_SUPPLY)
* M81 - Turn off Power Supply. (Requires POWER_SUPPLY)
* M82 - Set E codes absolute (default).
* M83 - Set E codes relative while in Absolute (G90) mode.
* M84 - Disable steppers until next move, or use S<seconds> to specify an idle
* duration after which steppers should turn off. S0 disables the timeout.
* M85 - Set inactivity shutdown timer with parameter S<seconds>. To disable set zero (default)
* M92 - Set planner.axis_steps_per_mm for one or more axes.
* M104 - Set extruder target temp.
* M105 - Report current temperatures.
* M106 - Fan on.
* M107 - Fan off.
* M108 - Break out of heating loops (M109, M190, M303). With no controller, breaks out of M0/M1. (Requires EMERGENCY_PARSER)
* 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
* M110 - Set the current line number. (Used by host printing)
* M111 - Set debug flags: "M111 S<flagbits>". See flag bits defined in enum.h.
* M112 - Emergency stop.
* M113 - Get or set the timeout interval for Host Keepalive "busy" messages. (Requires HOST_KEEPALIVE_FEATURE)
* M114 - Report current position.
* M115 - Report capabilities. (Extended capabilities requires EXTENDED_CAPABILITIES_REPORT)
* M117 - Display a message on the controller screen. (Requires an LCD)
* M119 - Report endstops status.
* M120 - Enable endstops detection.
* M121 - Disable endstops detection.
* M126 - Solenoid Air Valve Open. (Requires BARICUDA)
* M127 - Solenoid Air Valve Closed. (Requires BARICUDA)
* M128 - EtoP Open. (Requires BARICUDA)
* M129 - EtoP Closed. (Requires BARICUDA)
* M140 - Set bed target temp. S<temp>
* M145 - Set heatup values for materials on the LCD. H<hotend> B<bed> F<fan speed> for S<material> (0=PLA, 1=ABS)
* M149 - Set temperature units. (Requires TEMPERATURE_UNITS_SUPPORT)
* M150 - Set Status LED Color as R<red> U<green> B<blue>. Values 0-255. (Requires BLINKM or RGB_LED)
* M155 - Auto-report temperatures with interval of S<seconds>. (Requires AUTO_REPORT_TEMPERATURES)
* M163 - Set a single proportion for a mixing extruder. (Requires MIXING_EXTRUDER)
* M164 - Save the mix as a virtual extruder. (Requires MIXING_EXTRUDER and MIXING_VIRTUAL_TOOLS)
* M165 - Set the proportions for a mixing extruder. Use parameters ABCDHI to set the mixing factors. (Requires MIXING_EXTRUDER)
* 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 for heating or cooling. **
* M200 - Set filament diameter, D<diameter>, setting E axis units to cubic. (Use S0 to revert to linear units.)
* M201 - Set max acceleration in units/s^2 for print moves: "M201 X<accel> Y<accel> Z<accel> E<accel>"
* M202 - Set max acceleration in units/s^2 for travel moves: "M202 X<accel> Y<accel> Z<accel> E<accel>" ** UNUSED IN MARLIN! **
* M203 - Set maximum feedrate: "M203 X<fr> Y<fr> Z<fr> E<fr>" in units/sec.
* M204 - Set default acceleration in units/sec^2: P<printing> R<extruder_only> T<travel>
* M205 - Set advanced settings. Current units apply:
S<print> T<travel> minimum speeds
B<minimum segment time>
X<max X jerk>, Y<max Y jerk>, Z<max Z jerk>, E<max E jerk>
* M206 - Set additional homing offset.
* M207 - Set Retract Length: S<length>, Feedrate: F<units/min>, and Z lift: Z<distance>. (Requires FWRETRACT)
* M208 - Set Recover (unretract) Additional (!) Length: S<length> and Feedrate: F<units/min>. (Requires FWRETRACT)
* M209 - Turn Automatic Retract Detection on/off: S<0|1> (For slicers that don't support G10/11). (Requires FWRETRACT)
Every normal extrude-only move will be classified as retract depending on the direction.
* M211 - Enable, Disable, and/or Report software endstops: S<0|1>
* M218 - Set a tool offset: "M218 T<index> X<offset> Y<offset>". (Requires 2 or more extruders)
* M220 - Set Feedrate Percentage: "M220 S<percent>" (i.e., "FR" on the LCD)
* M221 - Set Flow Percentage: "M221 S<percent>"
* M226 - Wait until a pin is in a given state: "M226 P<pin> S<state>"
* M240 - Trigger a camera to take a photograph. (Requires CHDK or PHOTOGRAPH_PIN)
* M250 - Set LCD contrast: "M250 C<contrast>" (0-63). (Requires LCD support)
* M260 - i2c Send Data (Requires EXPERIMENTAL_I2CBUS)
* M261 - i2c Request Data (Requires EXPERIMENTAL_I2CBUS)
* M280 - Set servo position absolute: "M280 P<index> S<angle>". (Requires servos)
* M300 - Play beep sound S<frequency Hz> P<duration ms>
* M301 - Set PID parameters P I and D. (Requires PIDTEMP)
* M302 - Allow cold extrudes, or set the minimum extrude S<temperature>. (Requires PREVENT_COLD_EXTRUSION)
* M303 - PID relay autotune S<temperature> sets the target temperature. Default 150C. (Requires PIDTEMP)
* M304 - Set bed PID parameters P I and D. (Requires PIDTEMPBED)
* M355 - Turn the Case Light on/off and set its brightness. (Requires CASE_LIGHT_PIN)
* M380 - Activate solenoid on active extruder. (Requires EXT_SOLENOID)
* M381 - Disable all solenoids. (Requires EXT_SOLENOID)
* M400 - Finish all moves.
* M401 - Lower Z probe. (Requires a probe)
* M402 - Raise Z probe. (Requires a probe)
* M404 - Display or set the Nominal Filament Width: "W<diameter>". (Requires FILAMENT_WIDTH_SENSOR)
* M405 - Enable Filament Sensor flow control. "M405 D<delay_cm>". (Requires FILAMENT_WIDTH_SENSOR)
* M406 - Disable Filament Sensor flow control. (Requires FILAMENT_WIDTH_SENSOR)
* M407 - Display measured filament diameter in millimeters. (Requires FILAMENT_WIDTH_SENSOR)
* M410 - Quickstop. Abort all planned moves.
* M420 - Enable/Disable Leveling (with current values) S1=enable S0=disable (Requires MESH_BED_LEVELING or ABL)
* M421 - Set a single Z coordinate in the Mesh Leveling grid. X<units> Y<units> Z<units> (Requires MESH_BED_LEVELING)
* M428 - Set the home_offset based on the current_position. Nearest edge applies.
* M500 - Store parameters in EEPROM. (Requires EEPROM_SETTINGS)
* M501 - Restore parameters from EEPROM. (Requires EEPROM_SETTINGS)
* M502 - Revert to the default "factory settings". ** Does not write them to EEPROM! **
* M503 - Print the current settings (in memory): "M503 S<verbose>". S0 specifies compact output.
* M540 - Enable/disable SD card abort on endstop hit: "M540 S<state>". (Requires ABORT_ON_ENDSTOP_HIT_FEATURE_ENABLED)
* M600 - Pause for filament change: "M600 X<pos> Y<pos> Z<raise> E<first_retract> L<later_retract>". (Requires FILAMENT_CHANGE_FEATURE)
* M665 - Set delta configurations: "M665 L<diagonal rod> R<delta radius> S<segments/s>" (Requires DELTA)
* M666 - Set delta endstop adjustment. (Requires DELTA)
* M605 - Set dual x-carriage movement mode: "M605 S<mode> [X<x_offset>] [R<temp_offset>]". (Requires DUAL_X_CARRIAGE)
* M851 - Set Z probe's Z offset in current units. (Negative = below the nozzle.)
* M907 - Set digital trimpot motor current using axis codes. (Requires a board with digital trimpots)
* M908 - Control digital trimpot directly. (Requires DAC_STEPPER_CURRENT or DIGIPOTSS_PIN)
* M909 - Print digipot/DAC current value. (Requires DAC_STEPPER_CURRENT)
* M910 - Commit digipot/DAC value to external EEPROM via I2C. (Requires DAC_STEPPER_CURRENT)
* M350 - Set microstepping mode. (Requires digital microstepping pins.)
* M351 - Toggle MS1 MS2 pins directly. (Requires digital microstepping pins.)
*
* ************ SCARA Specific - This can change to suit future G-code regulations
* M360 - SCARA calibration: Move to cal-position ThetaA (0 deg calibration)
* M361 - SCARA calibration: Move to cal-position ThetaB (90 deg calibration - steps per degree)
* M362 - SCARA calibration: Move to cal-position PsiA (0 deg calibration)
* M363 - SCARA calibration: Move to cal-position PsiB (90 deg calibration - steps per degree)
* M364 - SCARA calibration: Move to cal-position PSIC (90 deg to Theta calibration position)
* ************* SCARA End ***************
*
* ************ Custom codes - This can change to suit future G-code regulations
* M100 - Watch Free Memory (For Debugging). (Requires M100_FREE_MEMORY_WATCHER)
* M928 - Start SD logging: "M928 filename.gco". Stop with M29. (Requires SDSUPPORT)
* M999 - Restart after being stopped by error
*
* "T" Codes
*
* T0-T3 - Select an extruder (tool) by index: "T<n> F<units/min>"
*
*/
相關工具：Arduino、Keil