Merged in zpl's latest changes to Network and Print Monitor modules,
providing DHCP and Netbios name support
Added command M999 S4321 to unlock flash memory, reset and boot to BOSSA
port
Z dive height is now relative to Z probe trigger height and default is
reduced to 3mm
Added experimental support for acoustic probe for delta printers
Bug fix: firmware once again prevents Z homing before X and Y are homed,
if the Z probe is used for Z homing
Various code tidying
Fixed bug that caused the cooling fan PWM frequency to be 165kHz. It is
now 25kHz.
Fan RPM is now included in the web interface status response (thanks
zpl).
Many more error messages are now reported to the web interface as well
as the USB interface.
Interrupt-driven network timer task to better cope with slow SD card
writes (thanks zpl)
Module SamNonDuePin is now used for all digital and PWM pin I/O.
Changed network startup to avoid long delay if no network cable is
connected
Enable DHCP support if IP address is configured as 0.0.0.0 (not working
yet)
Move thermistor parameters to M305, added parameter to configure series
resistance
Added B and W PID parameters
