docs: LinuxMCU doc & script (#2956)

Signed-off-by: Lucio Tarantino <lucio.tarantino@gmail.com>

config/sample-raspberry-pi.cfg

@@ -0,0 +1,45 @@
+# This file contains an example configuration with RPi as secondary mcu
+
+# See both the example.cfg and example-extras.cfg file for a
+# description of available parameters.
+
+# The rpi microcontroller is used as secondary.
+# Typically, both the X and Y axes
+# are connected to the main micro-controller. The rpi microcontroller is used
+# on non time-critical functions such as enclosure sensors, additional fan or
+# light sources
+[mcu host]
+serial: /tmp/klipper_host_mcu
+
+# Example1: A led strip controlled by the GPIO20 on the RPi
+[output_pin caselight]
+pin: host:gpio20
+# You can also write the pin in extended form by specifying
+# the reference gpiochip.
+#pin: host:gpiochip0/gpio20
+
+[gcode_macro TOGGLE_CASELIGHT]
+gcode:
+  SET_PIN PIN=caselight VALUE={(not printer['output_pin caselight'].value)|int}
+
+
+# Example2: Using the i2c bus of the RPi to read a sensor
+[temperature_sensor enclosure_temp]
+sensor_type: HTU21D
+i2c_mcu: host
+i2c_bus: i2c.1
+htu21d_hold_master: False
+
+[gcode_macro QUERY_ENCLOSURE]
+default_parameter_SENSOR: htu21d enclosure_temp
+gcode:
+    {printer.gcode.action_respond_info(
+        "Temperature: %.2f C\n"
+        "Humidity: %.2f%%" % (
+            printer[SENSOR].temperature,
+            printer[SENSOR].humidity))}
+
+# Example 3:Using a pin on another gpiochip connected to the RPi
+# (in this case on an MCP23017)
+[fan]
+pin: host:gpiochip2/gpio7

docs/RPi_microcontroller.md

@@ -0,0 +1,148 @@
+This document describes the process of running Klipper on a RPi
+and use the same RPi as secondary mcu.
+
+Why use RPi as a secondary MCU?
+===============================
+Often the MCUs dedicated to controlling 3D printers have a limited and
+pre-configured number of exposed pins to manage the main printing
+functions (thermal resistors, extruders, steppers ...).
+Using the RPi where Klipper is installed as a secondary MCU gives the
+possibility to directly use the GPIOs and the buses (i2c, spi) of the RPi
+inside klipper without using Octoprint plugins (if used) or external
+programs giving the ability to control everything within the print GCODE.
+
+**Warning**: If your platform is a _Beaglebone_ and you have correctly followed the installation steps, the linux mcu is already installed and configured for your system.
+
+Install the rc script
+=====================
+
+If you want to use the host as a secondary MCU the klipper_mcu process must run before the klippy process.
+
+After installing Klipper, install the script. run:
+```
+cd ~/klipper/
+sudo cp "./scripts/klipper-mcu-start.sh" /etc/init.d/klipper_mcu
+sudo update-rc.d klipper_mcu defaults
+```
+
+Building the micro-controller code
+==================================
+
+To compile the Klipper micro-controller code, start by configuring it
+for the "Linux process":
+```
+cd ~/klipper/
+make menuconfig
+```
+
+To build and install the new micro-controller code, run:
+```
+sudo service klipper stop
+make flash
+sudo service klipper start
+```
+
+Remaining configuration
+=======================
+
+Complete the installation by configuring Klipper secondary MCU
+following the instructions in
+[RasperryPi example config](../config/example-rasperry-pi.cfg) and
+[Multi MCU example config](../config/example-multi-mcu.cfg).
+
+Optional: Identify the correct gpiochip
+=======================================
+On Rasperry and on many clones the pins exposed on the GPIO belong to the first gpiochip. They can therefore be used on klipper simply by referring them with the name `gpio0..n`.
+However, there are cases in which the exposed pins belong to gpiochips other than the first. For example in the case of some OrangePi models or if a Port Expander is used. In these cases it is useful to use the commands to access the _Linux GPIO character device_ to verify the configuration.
+
+To install the _Linux GPIO character device - binary_ on a debian based distro like octopi run:
+```
+sudo apt-get install gpiod
+```
+
+To check available gpiochip run:
+```
+gpiodetect
+```
+
+To check the pin number and the pin availability tun:
+```
+gpioinfo
+```
+
+The chosen pin can thus be used within the configuration as `gpiochip<n>/gpio<o>` where **n** is the chip number as seen by the `gpiodetect` command and **o** is the line number seen by the` gpioinfo` command.
+
+***Warning:*** only gpio marked as `unused` can be used. It is not possible for a _line_ to be used by multiple processes simultaneously.
+
+For example on a RPi 3B+ where klipper use the GPIO20 for a switch:
+```
+$ gpiodetect
+gpiochip0 [pinctrl-bcm2835] (54 lines)
+gpiochip1 [raspberrypi-exp-gpio] (8 lines)
+
+$ gpioinfo
+gpiochip0 - 54 lines:
+        line   0:      unnamed       unused   input  active-high
+        line   1:      unnamed       unused   input  active-high
+        line   2:      unnamed       unused   input  active-high
+        line   3:      unnamed       unused   input  active-high
+        line   4:      unnamed       unused   input  active-high
+        line   5:      unnamed       unused   input  active-high
+        line   6:      unnamed       unused   input  active-high
+        line   7:      unnamed       unused   input  active-high
+        line   8:      unnamed       unused   input  active-high
+        line   9:      unnamed       unused   input  active-high
+        line  10:      unnamed       unused   input  active-high
+        line  11:      unnamed       unused   input  active-high
+        line  12:      unnamed       unused   input  active-high
+        line  13:      unnamed       unused   input  active-high
+        line  14:      unnamed       unused   input  active-high
+        line  15:      unnamed       unused   input  active-high
+        line  16:      unnamed       unused   input  active-high
+        line  17:      unnamed       unused   input  active-high
+        line  18:      unnamed       unused   input  active-high
+        line  19:      unnamed       unused   input  active-high
+        line  20:      unnamed    "klipper"  output  active-high [used]
+        line  21:      unnamed       unused   input  active-high
+        line  22:      unnamed       unused   input  active-high
+        line  23:      unnamed       unused   input  active-high
+        line  24:      unnamed       unused   input  active-high
+        line  25:      unnamed       unused   input  active-high
+        line  26:      unnamed       unused   input  active-high
+        line  27:      unnamed       unused   input  active-high
+        line  28:      unnamed       unused   input  active-high
+        line  29:      unnamed       "led0"  output  active-high [used]
+        line  30:      unnamed       unused   input  active-high
+        line  31:      unnamed       unused   input  active-high
+        line  32:      unnamed       unused   input  active-high
+        line  33:      unnamed       unused   input  active-high
+        line  34:      unnamed       unused   input  active-high
+        line  35:      unnamed       unused   input  active-high
+        line  36:      unnamed       unused   input  active-high
+        line  37:      unnamed       unused   input  active-high
+        line  38:      unnamed       unused   input  active-high
+        line  39:      unnamed       unused   input  active-high
+        line  40:      unnamed       unused   input  active-high
+        line  41:      unnamed       unused   input  active-high
+        line  42:      unnamed       unused   input  active-high
+        line  43:      unnamed       unused   input  active-high
+        line  44:      unnamed       unused   input  active-high
+        line  45:      unnamed       unused   input  active-high
+        line  46:      unnamed       unused   input  active-high
+        line  47:      unnamed       unused   input  active-high
+        line  48:      unnamed       unused   input  active-high
+        line  49:      unnamed       unused   input  active-high
+        line  50:      unnamed       unused   input  active-high
+        line  51:      unnamed       unused   input  active-high
+        line  52:      unnamed       unused   input  active-high
+        line  53:      unnamed       unused   input  active-high
+gpiochip1 - 8 lines:
+        line   0:      unnamed       unused   input  active-high
+        line   1:      unnamed       unused   input  active-high
+        line   2:      unnamed       "led1"  output   active-low [used]
+        line   3:      unnamed       unused   input  active-high
+        line   4:      unnamed       unused   input  active-high
+        line   5:      unnamed       unused   input  active-high
+        line   6:      unnamed       unused   input  active-high
+        line   7:      unnamed       unused   input  active-high
+```

scripts/flash-linux.sh

@@ -15,6 +15,12 @@ sync
 
 # Restart (if system install script present)
 if [ -f /etc/init.d/klipper_pru ]; then
-    echo "Attempting host MCU restart..."
+    echo "Attempting host PRU restart..."
     service klipper_pru restart
 fi
+
+# Restart (if system install script present)
+if [ -f /etc/init.d/klipper_mcu ]; then
+    echo "Attempting host MCU restart..."
+    service klipper_mcu restart
+fi

scripts/klipper-mcu-start.sh

@@ -0,0 +1,78 @@
+#!/bin/sh
+# System startup script to start the MCU Linux firmware
+
+### BEGIN INIT INFO
+# Provides:          klipper_mcu
+# Required-Start:    $local_fs
+# Required-Stop:
+# Default-Start:     3 4 5
+# Default-Stop:      0 1 2 6
+# Short-Description: Klipper_MCU daemon
+# Description:       Starts the MCU for Klipper.
+### END INIT INFO
+
+PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
+DESC="klipper_mcu startup"
+NAME="klipper_mcu"
+KLIPPER_HOST_MCU=/usr/local/bin/klipper_mcu
+KLIPPER_HOST_ARGS="-r"
+PIDFILE=/var/run/klipper_mcu.pid
+
+. /lib/lsb/init-functions
+
+mcu_host_stop()
+{
+    # Shutdown existing Klipper instance (if applicable). The goal is to
+    # put the GPIO pins in a safe state.
+    if [ -c /tmp/klipper_host_mcu ]; then
+        log_daemon_msg "Attempting to shutdown host mcu..."
+        set -e
+        ( echo "FORCE_SHUTDOWN" > /tmp/klipper_host_mcu ) 2> /dev/null || ( log_action_msg "Firmware busy! Please shutdown Klipper and then retry." && exit 1 )
+        sleep 1
+        ( echo "FORCE_SHUTDOWN" > /tmp/klipper_host_mcu ) 2> /dev/null || ( log_action_msg "Firmware busy! Please shutdown Klipper and then retry." && exit 1 )
+        sleep 1
+        set +e
+    fi
+
+    log_daemon_msg "Stopping klipper host mcu" $NAME
+    killproc -p $PIDFILE $KLIPPER_HOST_MCU
+}
+
+mcu_host_start()
+{
+    [ -x $KLIPPER_HOST_MCU ] || return
+
+    if [ -c /tmp/klipper_host_mcu ]; then
+        mcu_host_stop
+    fi
+
+    log_daemon_msg "Starting klipper MCU" $NAME
+    start-stop-daemon --start --quiet --exec $KLIPPER_HOST_MCU \
+                      --background --pidfile $PIDFILE --make-pidfile \
+                      -- $KLIPPER_HOST_ARGS
+    log_end_msg $?
+}
+
+case "$1" in
+start)
+    mcu_host_start
+    ;;
+stop)
+    mcu_host_stop
+    ;;
+restart)
+    $0 stop
+    $0 start
+    ;;
+reload|force-reload)
+    log_daemon_msg "Reloading configuration not supported" $NAME
+    log_end_msg 1
+    ;;
+status)
+    status_of_proc -p $PIDFILE $KLIPPER_HOST_MCU $NAME && exit 0 || exit $?
+    ;;
+*)  log_action_msg "Usage: /etc/init.d/klipper_mcu {start|stop|status|restart|reload|force-reload}"
+    exit 2
+    ;;
+esac
+exit 0