A partial backup is needed in scenarios where the extruder may be
parked after a print is saved. For example during a blocking wait for the user in M600
Or during a MMU error screen.
A sudden power panic at this point would previously save the parked position
into EEPROM. When the print is recovered it would print in mid air.
1) current_position[Z_AXIS] is not always correct. saved_pos[Z_AXIS]
should always represent the correct resume position for the Z-axis
2) Use the saved position to fetch the Z-offset value from
the mesh bed leveling grid. In case the extruder is parked during
power panic, the previous code may extract the wrong mesh
bed leveling offset (due to extruder being located at different
X and Y axis coordinates)
I verified via printf that sizeof(saved_start_position) = 16 (i.e. 4 float values)
We simply want to write 16 bytes to address
EEPROM_UVLO_SAVED_START_POSITION
Change in memory:
Flash: -160 bytes
SRAM: 0 bytes
This allows us to restore the position of all axis saved in RAM
If the extruder had been parked to the side for example
due to filament runout. Then the original position (before parking)
should now be restored
Change in memory:
Flash: +40 bytes
SRAM: 0 bytes
If a print has been saved to RAM such as during a filament runout,
do not overwrite these saved values if a sudden
power panic appears.
Additionally, change the saved types to be the same as power panic when saving to RAM:
- Bed target temperature is uint8_t (0 to 255) instead of float
- Extruder target temperature is uint16_t instead of float
Doing this change allows us to re-use the same global variables and
avoid creating local variables during power panic.
Change in memory:
Flash: -246 bytes
SRAM: -5 bytes
Guðni Már Gilbert