Saving G29 Bed Level Correction Matrix to EEPROM

[printbus]

ultralcd_implementation_hitachi_HD44780.h

I get it to compile with this tab from my standard firmware.

Um, yeah. That file uses a different approach to include the liquidTWI2.h file. It'll search the directory with the rest of the source files (eg. tabs I guess). The standard Marlin file will expect liquidTWI2 to be installed in the Arduino libraries area - just what configuration.h says.

FOLLOWUP COMMENT: In configuration.h, uncommenting the #define for LCD_I2C_VIKI invokes a #define for LCD_I2C_TYPE_MC23017. Look for the ifdefs for that string in the two ultralcd_implementation_hitachi_HD44780.h files. The statement #include "LiquidTWI2.h" says search in the source directory first for this file, and then search in the libraries area. The Marlin statement #include <LiquidTWI2.h> says don't look in the source directory - just search the libraries area. Eric Zalm likely didn't want to include the LiquidTWI2 library as part of the Marlin distribution, perhaps because it is a third party library not unique to Marlin or the 3D printer application. There may be other more subtle differences between the two files - I didn't compare the details.