Saving G29 Bed Level Correction Matrix to EEPROM

[Roxy]

Several people have expressed an interest in not having to perform a G29 Auto Bed Leveling command prior to each print. This post has the instructions to do that. However, it has not been tested yet. My printer's power supply died and it will be a while until I can replace it. The changes and theory are fairly simple, but with that said, when this many trivial changes get made, usually something doesn't work right. If you proceed with that warning and run into a problem, just make a post detailing what is wrong and I'm pretty sure we can get the problem fixed.

The theory is simple. The EEPROM (if enabled in Marlin's Configuration.h file) can save many settings that override the default settings. The changes we will make will stop the G28 homing command from resetting the Bed Level Correction Matrix. Instead, we will only do that when a G29 command is issued. Once this is accomplished, we just need to add a small amount of support to the EEPROM routines to make them smart enough to save and restore this matrix besides all of the other values they already save and restore. And of course, we add some code so the matrix can be printed out also.

To use the code, the user would first issue a M502 (Restore Default Settings) command followed by a M500 (Save Current Settings to EEPROM). This is necessary to do once because the format of the data stored in the EEPROM is going to change. By doing a M502 followed by a M500 command we are forcing the EEPROM to conform to the new data format which includes space for the Bed Level Correction matrix. Failure to do this is going to result in your printer restoring all kinds of bad values from EEPROM into important variables that it uses to behave in a sane and rational way.

Once the EEPROM is made aware of the new configuration, you need to issue a G28 followed by a suitable G29 command and if the values work as expected, an M500 command. From then on, you will only use the G29 command if you don't see the first layer going down perfect. The M500 will store the Bed Level Correction Matrix so the next time the Marlin firmware initializes itself, it will grab the last saved matrix.

To make the firmware changes do the following:

In Configuration.h find:

#define ENABLE_AUTO_BED_LEVELING // Delete the comment to enable (remove // at the start of the line)
#define Z_PROBE_REPEATABILITY_TEST  // If not commented out, Z-Probe Repeatability test will be included if Auto Bed Leveling is Enabled.

In order to do this in a fully legitimate manner, we need to be able to control whether the feature is turned on or not. This will be required to get these enhancements folded back into the main code base. Change this code to:

#define ENABLE_AUTO_BED_LEVELING // Delete the comment to enable (remove // at the start of the line)
#define Z_PROBE_REPEATABILITY_TEST  // If not commented out, Z-Probe Repeatability test will be included if Auto Bed Leveling is Enabled.
#define SAVE_G29_CORRECTION_MATRIX  // if not commented out and the EEPROM is used to save settings, the G29 information will also be saved.

In Marlin_main.cpp find:

case 28: //G28 Home all Axis one at a time
#ifdef ENABLE_AUTO_BED_LEVELING
    plan_bed_level_matrix.set_to_identity();  //Reset the plane ("erase" all leveling data)
#endif //ENABLE_AUTO_BED_LEVELING

We don't want the G28 to reset our Bed Level Correction Matrix anymore. We want it left alone when the printer is Homed.
Delete the last 3 of those lines so you only have:

case 28: //G28 Home all Axis one at a time

We do want the G29 to start with a reset Bed Level Correction Matrix. This used to happen because a G28 is always issued prior to doing a G29. But with the G28 not clearing the matrix, we need to do it in the G29 now. Find the following lines:

#ifdef ENABLE_AUTO_BED_LEVELING
    case 29: // G29 Detailed Z-Probe, probes the bed at 3 or more points.
        {
            #if Z_MIN_PIN == -1
            #error "You must have a Z_MIN endstop in order to enable Auto Bed Leveling feature!!! Z_MIN_PIN must point to a valid hardware pin."
            #endif

Add the line deleted after them. Change them to be:

#ifdef ENABLE_AUTO_BED_LEVELING
    case 29: // G29 Detailed Z-Probe, probes the bed at 3 or more points.
        {
            #if Z_MIN_PIN == -1
            #error "You must have a Z_MIN endstop in order to enable Auto Bed Leveling feature!!! Z_MIN_PIN must point to a valid hardware pin."
            #endif
            plan_bed_level_matrix.set_to_identity();  //Reset the plane ("erase" all leveling data)

We need to make the bulk of the changes in ConfigurationStore.cpp. This is the file that handles the functionality of saving and restoring values from the EEPROM. Find:

void Config_StoreSettings() 
{
  char ver[4]= "000";
  int i=EEPROM_OFFSET;
  EEPROM_WRITE_VAR(i,ver); // invalidate data first 
  EEPROM_WRITE_VAR(i,axis_steps_per_unit);
  EEPROM_WRITE_VAR(i,max_feedrate);  
  EEPROM_WRITE_VAR(i,max_acceleration_units_per_sq_second);
  EEPROM_WRITE_VAR(i,acceleration);

Now when a M500 command is given, we want it to store the Bed Level Correction Matrix. Change this code block to:

void Config_StoreSettings() 
{
  char ver[4]= "000";
  int i=EEPROM_OFFSET;   
  EEPROM_WRITE_VAR(i,ver); // invalidate data first 
  EEPROM_WRITE_VAR(i,axis_steps_per_unit);
  EEPROM_WRITE_VAR(i,max_feedrate);  
  EEPROM_WRITE_VAR(i,max_acceleration_units_per_sq_second);
  EEPROM_WRITE_VAR(i,acceleration);
#ifdef SAVE_G29_CORRECTION_MATRIX
  EEPROM_WRITE_VAR(i,plan_bed_level_matrix);
#endif

And of course, we need to be able to get those values back out of the EEPROM when the printer resets and the firmware re-initializes itself. Find:

void Config_RetrieveSettings()
{
    int i=EEPROM_OFFSET;
    char stored_ver[4];
    char ver[4]=EEPROM_VERSION;
    EEPROM_READ_VAR(i,stored_ver); //read stored version
    //  SERIAL_ECHOLN("Version: [" << ver << "] Stored version: [" << stored_ver << "]");
    if (strncmp(ver,stored_ver,3) == 0)
    {
        // version number match
        EEPROM_READ_VAR(i,axis_steps_per_unit);
        EEPROM_READ_VAR(i,max_feedrate);  
        EEPROM_READ_VAR(i,max_acceleration_units_per_sq_second);
        
        // steps per sq second need to be updated to agree with the  units per sq second (as they are what is used in the planner)
        reset_acceleration_rates();
        
        EEPROM_READ_VAR(i,acceleration);

Change it to:

void Config_RetrieveSettings()
{
    int i=EEPROM_OFFSET;
    char stored_ver[4];
    char ver[4]=EEPROM_VERSION;
    EEPROM_READ_VAR(i,stored_ver); //read stored version
    //  SERIAL_ECHOLN("Version: [" << ver << "] Stored version: [" << stored_ver << "]");
    if (strncmp(ver,stored_ver,3) == 0)
    {
        // version number match
        EEPROM_READ_VAR(i,axis_steps_per_unit);
        EEPROM_READ_VAR(i,max_feedrate);  
        EEPROM_READ_VAR(i,max_acceleration_units_per_sq_second);
        
        // steps per sq second need to be updated to agree with the  units per sq second (as they are what is used in the planner)
        reset_acceleration_rates();
        
        EEPROM_READ_VAR(i,acceleration);
#ifdef SAVE_G29_CORRECTION_MATRIX
        EEPROM_READ_VAR(i,plan_bed_level_matrix);
#endif

Just to be clean, we want to fully support the M502 command to reset everything to a default state. Setting the Bed Level Correction matrix to unity makes sense. Find:

void Config_ResetDefault()
{
    float tmp1[]=DEFAULT_AXIS_STEPS_PER_UNIT;
    float tmp2[]=DEFAULT_MAX_FEEDRATE;
    long tmp3[]=DEFAULT_MAX_ACCELERATION;

Change it to:

void Config_ResetDefault()
{
    float tmp1[]=DEFAULT_AXIS_STEPS_PER_UNIT;
    float tmp2[]=DEFAULT_MAX_FEEDRATE;
    long tmp3[]=DEFAULT_MAX_ACCELERATION;
#ifdef SAVE_G29_CORRECTION_MATRIX
    plan_bed_level_matrix.set_to_identity();
#endif

And of course, we want to be able to print out all the settings in the EEPROM. So we need to teach it how to display the Bed Level Correction Matrix that it has stored for us. This command is invoked with the M503 command. Probably the spacing and new lines are not going to be right on this initial code. If it looks horrible, please make a post showing what it looks like and we can make a quick change to fix it. Find:

void Config_PrintSettings()
{  // Always have this function, even with EEPROM_SETTINGS disabled, the current values will be shown
    SERIAL_ECHO_START;
    SERIAL_ECHOLNPGM("Steps per unit:");
    SERIAL_ECHO_START;
    SERIAL_ECHOPAIR("  M92 X",axis_steps_per_unit[0]);
    SERIAL_ECHOPAIR(" Y",axis_steps_per_unit[1]);
    SERIAL_ECHOPAIR(" Z",axis_steps_per_unit[2]);
    SERIAL_ECHOPAIR(" E",axis_steps_per_unit[3]);
    SERIAL_ECHOLN("");

Chang it to:

void Config_PrintSettings()
{  // Always have this function, even with EEPROM_SETTINGS disabled, the current values will be shown
    SERIAL_ECHO_START;
    SERIAL_ECHOLNPGM("Steps per unit:");
    SERIAL_ECHO_START;
    SERIAL_ECHOPAIR("  M92 X",axis_steps_per_unit[0]);
    SERIAL_ECHOPAIR(" Y",axis_steps_per_unit[1]);
    SERIAL_ECHOPAIR(" Z",axis_steps_per_unit[2]);
    SERIAL_ECHOPAIR(" E",axis_steps_per_unit[3]);
    SERIAL_ECHOLN("");
#ifdef SAVE_G29_CORRECTION_MATRIX
    SERIAL_ECHO_START;
    plan_bed_level_matrix.debug("\n\nBed Level Correction Matrix:");
    SERIAL_ECHOLN("");
#endif

Good luck!