serial_bridge: Add serial bridge module

Add functionality that allows communicating and configuring
uart ports on the target MCU. Currently supports the STM32
architecture.

Signed-off-by: Jeremy Putnam <[email protected]>

config/printer-elegoo-neptune3-pro-2023.cfg

@@ -2,11 +2,17 @@
 # To use this config, during "make menuconfig" select the  STM32F401 with a
 # "32KiB bootloader" and serial (on USART1 PA10/PA9) communication.
 
+# For screen support, enable "Enable extra low-level configuration options"
+# and select "Enable serial bridge" and then "USART6" then uncommit the [neptune_screen]
+# and serial_bridge sections
+
+
 # Note that the "make flash" command does not work with ZNP Robin boards.
 # After running "make", rename the out/klipper.bin file to out/ZNP_ROBIN_NANO.bin
 # Copy the file out/ZNP_ROBIN_NANO.bin to an SD card formatted to FAT32
 # and then restart the printer with the SD card inserted.
 
+
 # See docs/Config_Reference.md for a description of parameters.
 
 # Core
@@ -22,6 +28,20 @@ max_accel: 3000
 max_z_velocity: 5
 max_z_accel: 100
 
+# Screen
+
+#[serial_bridge UART6]
+#rx_pin: PA12
+#tx_pin: PA11
+#baud: 115200
+#config: 4
+#eol:\xff\xff\xff
+
+#[neptune_screen]
+#serial_bridge: UART6
+#variant: 3Pro
+
+
 # Steppers
 
 [stepper_x]

docs/Config_Reference.md

@@ -4301,6 +4301,24 @@ information on menu attributes available during template rendering.
 #   mode start or end.
 ```
 
+### [neptune screen]
+Support for the Elegoo screen for the Neptune 3/3 Plus/3 Max.
+A [serial bridge](#serial_bridge) must be setup for communciation to
+take place. Communication is based on versions (1.4.2) and earlier.
+
+```
+[neptune_screen]
+#serial_bridge:
+#   Name of the serial_bridge to be used for communication
+#variant:
+#   The device variant to report to the screen. Possible values are
+#   3Pro: Neptune 3 Pro
+#   3Max: Neptune 3 Max
+#   3Plus: Neptune 3 Plus
+#   The default value is 3Pro
+#logging:
+#   Boolean used to enable/disable verbose logging. Default is False.
+```
 ## Filament sensors
 
 ### [filament_switch_sensor]
@@ -4735,3 +4753,34 @@ via the `i2c_speed` parameter. All other Klipper micro-controllers use a
 #   to 100000 and changing this value has no effect. The default is
 #   100000. Linux, RP2040 and ATmega support 400000.
 ```
+
+### [serial_bridge]
+Communication between the mcu and devices connected to its UART ports
+such as third-party screens can be bridged with this module. This feature
+must be enabled with the low-level configuration options when compiling the
+firmware specifying which ports should be available for the bridge to use.
+Currently only STM32 devices are supported.
+
+See the [command reference](G-Codes.md#serial_bridge) for the different
+options and configurations available.
+
+```
+[serial_bridge bridge_screen]
+#eol:
+#   The character or string of characters to be sent at the end of each
+#   call. Defaults to \n
+#baud
+#   The baud rate for communication. Default is 115200
+#config:
+#   The serial configuration to use. These define the port and pins.
+#   List them  using the [command reference](G-Codes.md#serial_bridge)
+#   SERIAL_BRIDGE_LIST_CONFIGS
+#tx_pin:
+#   Pin used for Tx. This is used to reserve the pin and to look up
+#   the appropriate MCU
+#rx_pin
+#   Pin used for Rx. This is used to reserve the pin and to look up
+#   the appropriate MCU
+#logging
+#   Boolean to turn logging of or on for debugging communication
+```

docs/G-Codes.md

@@ -1099,6 +1099,25 @@ loaded into the `printer.save_variables.variables` dict at startup and
 can be used in gcode macros. The provided VALUE is parsed as a Python
 literal.
 
+### [serial_bridge]
+The following command is enabled if a
+[serial_bridge config section](Config_Reference.md#serial_bridge)
+has been enabled.
+
+#### SERIAL_BRIDGE_SEND
+`SERIAL_BRIDGE_SEND [TEXT=<value>] [BRIDGE=<value>]`: This command will
+send a serial message (TEXT) to the bridge specificed (BRIDGE).
+
+#### SERIAL_BRIDGE_LIST_CONFIGS
+`SERIAL_BRIDGE_LIST_CONFIGS`: This command will list the available
+configurations reported by the MCU for use. This config should be used
+when setting up a new [serial_bridge](Config_Reference.md#serial_bridge).
+
+#### SERIAL_BRIDGE_LIST_BRIDGES
+`SERIAL_BRIDGE_LIST_BRIDGES`: This command will list the available
+bridges ready for use from the printer configuration
+[serial_bridge](Config_Reference.md#serial_bridge).
+
 ### [screws_tilt_adjust]
 
 The following commands are available when the