M303 - PID autotune

thermal Auto-tune the PID system to find stable values. PIDTEMP|PIDTEMPBED

This command initiates a process of heating and cooling to determine the proper PID values for the specified hotend or the heated bed.

Requires PIDTEMP or PIDTEMPBED.

View current PID values with M503.

If EEPROM_SETTINGS is enabled, all PID values are saved with M500, loaded with M501, and reset with M502.

M303 C<count> D<action> D<flag> [E<index>] S<temp> U<flag>

`C<count>`	Cycles. At least 3 cycles are required. Default 5.
`D<action>`	Toggle PID debug output on / off (and take no further action). (Requires `PID_DEBUG`)
`D<flag>`	Toggle activation of `PID_DEBUG` output.
`[E<index>]`	Hotend index (-1 for heated bed). Default 0.
`S<temp>`	Target temperature
`U<flag>`	Use PID result. (Otherwise just print it out.)

Auto-tune hotend at 210 °C for 8 cycles:

M303 E0 C8 S210

Auto-tune bed at 60 °C for 8 cycles:

M303 E-1 C8 S60