Implemented M155 and M156, a generic TWI/I2C interface for Marlin

Marlin/Configuration_adv.h

@@ -653,6 +653,38 @@ const unsigned int dropsegments = 5; //everything with less than this number of
 
 #endif
 
+/**
+ * TWI/I2C BUS
+ *
+ * This feature is an EXPERIMENTAL feature so it shall not be used on production
+ * machines. Enabling this will allow you to send and receive I2C data from slave
+ * devices on the bus.
+ *
+ * ; Example #1
+ * ; This macro send the string "Marlin" to the slave device with address 0x63
+ * ; It uses multiple M155 commands with one B<base 10> arg
+ * M155 A63  ; Target slave address
+ * M155 B77  ; M
+ * M155 B97  ; a
+ * M155 B114 ; r
+ * M155 B108 ; l
+ * M155 B105 ; i
+ * M155 B110 ; n
+ * M155 S1   ; Send the current buffer
+ *
+ * ; Example #2
+ * ; Request 6 bytes from slave device with address 0x63
+ * M156 A63 B5
+ *
+ * ; Example #3
+ * ; Example serial output of a M156 request
+ * echo:i2c-reply: from:63 bytes:5 data:hello
+ */
+
+// @section i2cbus
+
+//#define EXPERIMENTAL_I2CBUS
+
 #include "Conditionals.h"
 #include "SanityCheck.h"
 

Marlin/Marlin_main.cpp

@@ -77,6 +77,10 @@
   #include "stepper_dac.h"
 #endif
 
+#if ENABLED(EXPERIMENTAL_I2CBUS)
+  #include "twibus.h"
+#endif
+
 /**
  * Look here for descriptions of G-codes:
  *  - http://linuxcnc.org/handbook/gcode/g-code.html
@@ -248,6 +252,10 @@
   CardReader card;
 #endif
 
+#if ENABLED(EXPERIMENTAL_I2CBUS)
+  TWIBus i2c;
+#endif
+
 bool Running = true;
 
 uint8_t marlin_debug_flags = DEBUG_NONE;
@@ -4771,6 +4779,57 @@ inline void gcode_M121() { enable_endstops_globally(false); }
 
 #endif // BLINKM
 
+#if ENABLED(EXPERIMENTAL_I2CBUS)
+
+  /**
+   * M155: Send data to a I2C slave device
+   *
+   * This is a PoC, the formating and arguments for the GCODE will
+   * change to be more compatible, the current proposal is:
+   *
+   *  M155 A<slave device address base 10> ; Sets the I2C slave address the data will be sent to
+   *
+   *  M155 B<byte-1 value in base 10>
+   *  M155 B<byte-2 value in base 10>
+   *  M155 B<byte-3 value in base 10>
+   *
+   *  M155 S1 ; Send the buffered data and reset the buffer
+   *  M155 R1 ; Reset the buffer without sending data
+   *
+   */
+  inline void gcode_M155() {
+    // Set the target address
+    if (code_seen('A'))
+      i2c.address((uint8_t) code_value_short());
+
+    // Add a new byte to the buffer
+    else if (code_seen('B'))
+      i2c.addbyte((int) code_value_short());
+
+    // Flush the buffer to the bus
+    else if (code_seen('S')) i2c.send();
+
+    // Reset and rewind the buffer
+    else if (code_seen('R')) i2c.reset();
+  }
+
+  /**
+   * M156: Request X bytes from I2C slave device
+   *
+   * Usage: M156 A<slave device address base 10> B<number of bytes>
+   */
+  inline void gcode_M156() {
+    uint8_t addr = code_seen('A') ? code_value_short() : 0;
+    int bytes    = code_seen('B') ? code_value_short() : 0;
+
+    if (addr && bytes) {
+      i2c.address(addr);
+      i2c.reqbytes(bytes);
+    }
+  }
+
+#endif //EXPERIMENTAL_I2CBUS
+
 /**
  * M200: Set filament diameter and set E axis units to cubic millimeters
  *
@@ -6439,6 +6498,18 @@ void process_next_command() {
 
       #endif //BLINKM
 
+      #if ENABLED(EXPERIMENTAL_I2CBUS)
+
+        case 155:
+          gcode_M155();
+          break;
+
+        case 156:
+          gcode_M156();
+          break;
+
+      #endif //EXPERIMENTAL_I2CBUS
+
       case 200: // M200 D<millimeters> set filament diameter and set E axis units to cubic millimeters (use S0 to set back to millimeters).
         gcode_M200();
         break;

Marlin/example_configurations/Felix/Configuration_adv.h

@@ -653,6 +653,38 @@ const unsigned int dropsegments = 5; //everything with less than this number of
 
 #endif
 
+/**
+ * TWI/I2C BUS
+ *
+ * This feature is an EXPERIMENTAL feature so it shall not be used on production
+ * machines. Enabling this will allow you to send and receive I2C data from slave
+ * devices on the bus.
+ *
+ * ; Example #1
+ * ; This macro send the string "Marlin" to the slave device with address 0x63
+ * ; It uses multiple M155 commands with one B<base 10> arg
+ * M155 A63  ; Target slave address
+ * M155 B77  ; M
+ * M155 B97  ; a
+ * M155 B114 ; r
+ * M155 B108 ; l
+ * M155 B105 ; i
+ * M155 B110 ; n
+ * M155 S1   ; Send the current buffer
+ *
+ * ; Example #2
+ * ; Request 6 bytes from slave device with address 0x63
+ * M156 A63 B5
+ *
+ * ; Example #3
+ * ; Example serial output of a M156 request
+ * echo:i2c-reply: from:63 bytes:5 data:hello
+ */
+
+// @section i2cbus
+
+//#define EXPERIMENTAL_I2CBUS
+
 #include "Conditionals.h"
 #include "SanityCheck.h"
 

Marlin/example_configurations/Hephestos/Configuration_adv.h

@@ -653,6 +653,38 @@ const unsigned int dropsegments = 5; //everything with less than this number of
 
 #endif
 
+/**
+ * TWI/I2C BUS
+ *
+ * This feature is an EXPERIMENTAL feature so it shall not be used on production
+ * machines. Enabling this will allow you to send and receive I2C data from slave
+ * devices on the bus.
+ *
+ * ; Example #1
+ * ; This macro send the string "Marlin" to the slave device with address 0x63
+ * ; It uses multiple M155 commands with one B<base 10> arg
+ * M155 A63  ; Target slave address
+ * M155 B77  ; M
+ * M155 B97  ; a
+ * M155 B114 ; r
+ * M155 B108 ; l
+ * M155 B105 ; i
+ * M155 B110 ; n
+ * M155 S1   ; Send the current buffer
+ *
+ * ; Example #2
+ * ; Request 6 bytes from slave device with address 0x63
+ * M156 A63 B5
+ *
+ * ; Example #3
+ * ; Example serial output of a M156 request
+ * echo:i2c-reply: from:63 bytes:5 data:hello
+ */
+
+// @section i2cbus
+
+//#define EXPERIMENTAL_I2CBUS
+
 #include "Conditionals.h"
 #include "SanityCheck.h"
 

Marlin/example_configurations/Hephestos_2/Configuration_adv.h

@@ -653,6 +653,38 @@ const unsigned int dropsegments = 5; //everything with less than this number of
 
 #endif
 
+/**
+ * TWI/I2C BUS
+ *
+ * This feature is an EXPERIMENTAL feature so it shall not be used on production
+ * machines. Enabling this will allow you to send and receive I2C data from slave
+ * devices on the bus.
+ *
+ * ; Example #1
+ * ; This macro send the string "Marlin" to the slave device with address 0x63
+ * ; It uses multiple M155 commands with one B<base 10> arg
+ * M155 A63  ; Target slave address
+ * M155 B77  ; M
+ * M155 B97  ; a
+ * M155 B114 ; r
+ * M155 B108 ; l
+ * M155 B105 ; i
+ * M155 B110 ; n
+ * M155 S1   ; Send the current buffer
+ *
+ * ; Example #2
+ * ; Request 6 bytes from slave device with address 0x63
+ * M156 A63 B5
+ *
+ * ; Example #3
+ * ; Example serial output of a M156 request
+ * echo:i2c-reply: from:63 bytes:5 data:hello
+ */
+
+// @section i2cbus
+
+//#define EXPERIMENTAL_I2CBUS
+
 #include "Conditionals.h"
 #include "SanityCheck.h"
 

Marlin/example_configurations/K8200/Configuration_adv.h

@@ -659,6 +659,38 @@ const unsigned int dropsegments = 2; //everything with less than this number of
 
 #endif
 
+/**
+ * TWI/I2C BUS
+ *
+ * This feature is an EXPERIMENTAL feature so it shall not be used on production
+ * machines. Enabling this will allow you to send and receive I2C data from slave
+ * devices on the bus.
+ *
+ * ; Example #1
+ * ; This macro send the string "Marlin" to the slave device with address 0x63
+ * ; It uses multiple M155 commands with one B<base 10> arg
+ * M155 A63  ; Target slave address
+ * M155 B77  ; M
+ * M155 B97  ; a
+ * M155 B114 ; r
+ * M155 B108 ; l
+ * M155 B105 ; i
+ * M155 B110 ; n
+ * M155 S1   ; Send the current buffer
+ *
+ * ; Example #2
+ * ; Request 6 bytes from slave device with address 0x63
+ * M156 A63 B5
+ *
+ * ; Example #3
+ * ; Example serial output of a M156 request
+ * echo:i2c-reply: from:63 bytes:5 data:hello
+ */
+
+// @section i2cbus
+
+//#define EXPERIMENTAL_I2CBUS
+
 #include "Conditionals.h"
 #include "SanityCheck.h"
 

Marlin/example_configurations/RigidBot/Configuration_adv.h

@@ -653,6 +653,38 @@ const unsigned int dropsegments = 5; //everything with less than this number of
 
 #endif
 
+/**
+ * TWI/I2C BUS
+ *
+ * This feature is an EXPERIMENTAL feature so it shall not be used on production
+ * machines. Enabling this will allow you to send and receive I2C data from slave
+ * devices on the bus.
+ *
+ * ; Example #1
+ * ; This macro send the string "Marlin" to the slave device with address 0x63
+ * ; It uses multiple M155 commands with one B<base 10> arg
+ * M155 A63  ; Target slave address
+ * M155 B77  ; M
+ * M155 B97  ; a
+ * M155 B114 ; r
+ * M155 B108 ; l
+ * M155 B105 ; i
+ * M155 B110 ; n
+ * M155 S1   ; Send the current buffer
+ *
+ * ; Example #2
+ * ; Request 6 bytes from slave device with address 0x63
+ * M156 A63 B5
+ *
+ * ; Example #3
+ * ; Example serial output of a M156 request
+ * echo:i2c-reply: from:63 bytes:5 data:hello
+ */
+
+// @section i2cbus
+
+//#define EXPERIMENTAL_I2CBUS
+
 #include "Conditionals.h"
 #include "SanityCheck.h"
 

Marlin/example_configurations/SCARA/Configuration_adv.h

@@ -653,6 +653,38 @@ const unsigned int dropsegments = 5; //everything with less than this number of
 
 #endif
 
+/**
+ * TWI/I2C BUS
+ *
+ * This feature is an EXPERIMENTAL feature so it shall not be used on production
+ * machines. Enabling this will allow you to send and receive I2C data from slave
+ * devices on the bus.
+ *
+ * ; Example #1
+ * ; This macro send the string "Marlin" to the slave device with address 0x63
+ * ; It uses multiple M155 commands with one B<base 10> arg
+ * M155 A63  ; Target slave address
+ * M155 B77  ; M
+ * M155 B97  ; a
+ * M155 B114 ; r
+ * M155 B108 ; l
+ * M155 B105 ; i
+ * M155 B110 ; n
+ * M155 S1   ; Send the current buffer
+ *
+ * ; Example #2
+ * ; Request 6 bytes from slave device with address 0x63
+ * M156 A63 B5
+ *
+ * ; Example #3
+ * ; Example serial output of a M156 request
+ * echo:i2c-reply: from:63 bytes:5 data:hello
+ */
+
+// @section i2cbus
+
+//#define EXPERIMENTAL_I2CBUS
+
 #include "Conditionals.h"
 #include "SanityCheck.h"
 

Marlin/example_configurations/TAZ4/Configuration_adv.h

@@ -661,6 +661,38 @@ const unsigned int dropsegments = 5; //everything with less than this number of
 
 #endif
 
+/**
+ * TWI/I2C BUS
+ *
+ * This feature is an EXPERIMENTAL feature so it shall not be used on production
+ * machines. Enabling this will allow you to send and receive I2C data from slave
+ * devices on the bus.
+ *
+ * ; Example #1
+ * ; This macro send the string "Marlin" to the slave device with address 0x63
+ * ; It uses multiple M155 commands with one B<base 10> arg
+ * M155 A63  ; Target slave address
+ * M155 B77  ; M
+ * M155 B97  ; a
+ * M155 B114 ; r
+ * M155 B108 ; l
+ * M155 B105 ; i
+ * M155 B110 ; n
+ * M155 S1   ; Send the current buffer
+ *
+ * ; Example #2
+ * ; Request 6 bytes from slave device with address 0x63
+ * M156 A63 B5
+ *
+ * ; Example #3
+ * ; Example serial output of a M156 request
+ * echo:i2c-reply: from:63 bytes:5 data:hello
+ */
+
+// @section i2cbus
+
+//#define EXPERIMENTAL_I2CBUS
+
 #include "Conditionals.h"
 #include "SanityCheck.h"
 

Marlin/example_configurations/WITBOX/Configuration_adv.h

@@ -653,6 +653,38 @@ const unsigned int dropsegments = 5; //everything with less than this number of
 
 #endif
 
+/**
+ * TWI/I2C BUS
+ *
+ * This feature is an EXPERIMENTAL feature so it shall not be used on production
+ * machines. Enabling this will allow you to send and receive I2C data from slave
+ * devices on the bus.
+ *
+ * ; Example #1
+ * ; This macro send the string "Marlin" to the slave device with address 0x63
+ * ; It uses multiple M155 commands with one B<base 10> arg
+ * M155 A63  ; Target slave address
+ * M155 B77  ; M
+ * M155 B97  ; a
+ * M155 B114 ; r
+ * M155 B108 ; l
+ * M155 B105 ; i
+ * M155 B110 ; n
+ * M155 S1   ; Send the current buffer
+ *
+ * ; Example #2
+ * ; Request 6 bytes from slave device with address 0x63
+ * M156 A63 B5
+ *
+ * ; Example #3
+ * ; Example serial output of a M156 request
+ * echo:i2c-reply: from:63 bytes:5 data:hello
+ */
+
+// @section i2cbus
+
+//#define EXPERIMENTAL_I2CBUS
+
 #include "Conditionals.h"
 #include "SanityCheck.h"
 

Marlin/example_configurations/delta/biv2.5/Configuration_adv.h

@@ -655,6 +655,38 @@ const unsigned int dropsegments = 5; //everything with less than this number of
 
 #endif
 
+/**
+ * TWI/I2C BUS
+ *
+ * This feature is an EXPERIMENTAL feature so it shall not be used on production
+ * machines. Enabling this will allow you to send and receive I2C data from slave
+ * devices on the bus.
+ *
+ * ; Example #1
+ * ; This macro send the string "Marlin" to the slave device with address 0x63
+ * ; It uses multiple M155 commands with one B<base 10> arg
+ * M155 A63  ; Target slave address
+ * M155 B77  ; M
+ * M155 B97  ; a
+ * M155 B114 ; r
+ * M155 B108 ; l
+ * M155 B105 ; i
+ * M155 B110 ; n
+ * M155 S1   ; Send the current buffer
+ *
+ * ; Example #2
+ * ; Request 6 bytes from slave device with address 0x63
+ * M156 A63 B5
+ *
+ * ; Example #3
+ * ; Example serial output of a M156 request
+ * echo:i2c-reply: from:63 bytes:5 data:hello
+ */
+
+// @section i2cbus
+
+//#define EXPERIMENTAL_I2CBUS
+
 #include "Conditionals.h"
 #include "SanityCheck.h"
 

Marlin/example_configurations/delta/generic/Configuration_adv.h

@@ -655,6 +655,38 @@ const unsigned int dropsegments = 5; //everything with less than this number of
 
 #endif
 
+/**
+ * TWI/I2C BUS
+ *
+ * This feature is an EXPERIMENTAL feature so it shall not be used on production
+ * machines. Enabling this will allow you to send and receive I2C data from slave
+ * devices on the bus.
+ *
+ * ; Example #1
+ * ; This macro send the string "Marlin" to the slave device with address 0x63
+ * ; It uses multiple M155 commands with one B<base 10> arg
+ * M155 A63  ; Target slave address
+ * M155 B77  ; M
+ * M155 B97  ; a
+ * M155 B114 ; r
+ * M155 B108 ; l
+ * M155 B105 ; i
+ * M155 B110 ; n
+ * M155 S1   ; Send the current buffer
+ *
+ * ; Example #2
+ * ; Request 6 bytes from slave device with address 0x63
+ * M156 A63 B5
+ *
+ * ; Example #3
+ * ; Example serial output of a M156 request
+ * echo:i2c-reply: from:63 bytes:5 data:hello
+ */
+
+// @section i2cbus
+
+//#define EXPERIMENTAL_I2CBUS
+
 #include "Conditionals.h"
 #include "SanityCheck.h"
 

Marlin/example_configurations/delta/kossel_mini/Configuration_adv.h

@@ -654,6 +654,38 @@ const unsigned int dropsegments = 5; //everything with less than this number of
 
 #endif
 
+/**
+ * TWI/I2C BUS
+ *
+ * This feature is an EXPERIMENTAL feature so it shall not be used on production
+ * machines. Enabling this will allow you to send and receive I2C data from slave
+ * devices on the bus.
+ *
+ * ; Example #1
+ * ; This macro send the string "Marlin" to the slave device with address 0x63
+ * ; It uses multiple M155 commands with one B<base 10> arg
+ * M155 A63  ; Target slave address
+ * M155 B77  ; M
+ * M155 B97  ; a
+ * M155 B114 ; r
+ * M155 B108 ; l
+ * M155 B105 ; i
+ * M155 B110 ; n
+ * M155 S1   ; Send the current buffer
+ *
+ * ; Example #2
+ * ; Request 6 bytes from slave device with address 0x63
+ * M156 A63 B5
+ *
+ * ; Example #3
+ * ; Example serial output of a M156 request
+ * echo:i2c-reply: from:63 bytes:5 data:hello
+ */
+
+// @section i2cbus
+
+//#define EXPERIMENTAL_I2CBUS
+
 #include "Conditionals.h"
 #include "SanityCheck.h"
 

Marlin/example_configurations/delta/kossel_pro/Configuration_adv.h

@@ -659,6 +659,38 @@ const unsigned int dropsegments = 5; //everything with less than this number of
 
 #endif
 
+/**
+ * TWI/I2C BUS
+ *
+ * This feature is an EXPERIMENTAL feature so it shall not be used on production
+ * machines. Enabling this will allow you to send and receive I2C data from slave
+ * devices on the bus.
+ *
+ * ; Example #1
+ * ; This macro send the string "Marlin" to the slave device with address 0x63
+ * ; It uses multiple M155 commands with one B<base 10> arg
+ * M155 A63  ; Target slave address
+ * M155 B77  ; M
+ * M155 B97  ; a
+ * M155 B114 ; r
+ * M155 B108 ; l
+ * M155 B105 ; i
+ * M155 B110 ; n
+ * M155 S1   ; Send the current buffer
+ *
+ * ; Example #2
+ * ; Request 6 bytes from slave device with address 0x63
+ * M156 A63 B5
+ *
+ * ; Example #3
+ * ; Example serial output of a M156 request
+ * echo:i2c-reply: from:63 bytes:5 data:hello
+ */
+
+// @section i2cbus
+
+//#define EXPERIMENTAL_I2CBUS
+
 #include "Conditionals.h"
 #include "SanityCheck.h"
 

Marlin/example_configurations/delta/kossel_xl/Configuration_adv.h

@@ -653,6 +653,38 @@ const unsigned int dropsegments = 5; //everything with less than this number of
 
 #endif
 
+/**
+ * TWI/I2C BUS
+ *
+ * This feature is an EXPERIMENTAL feature so it shall not be used on production
+ * machines. Enabling this will allow you to send and receive I2C data from slave
+ * devices on the bus.
+ *
+ * ; Example #1
+ * ; This macro send the string "Marlin" to the slave device with address 0x63
+ * ; It uses multiple M155 commands with one B<base 10> arg
+ * M155 A63  ; Target slave address
+ * M155 B77  ; M
+ * M155 B97  ; a
+ * M155 B114 ; r
+ * M155 B108 ; l
+ * M155 B105 ; i
+ * M155 B110 ; n
+ * M155 S1   ; Send the current buffer
+ *
+ * ; Example #2
+ * ; Request 6 bytes from slave device with address 0x63
+ * M156 A63 B5
+ *
+ * ; Example #3
+ * ; Example serial output of a M156 request
+ * echo:i2c-reply: from:63 bytes:5 data:hello
+ */
+
+// @section i2cbus
+
+//#define EXPERIMENTAL_I2CBUS
+
 #include "Conditionals.h"
 #include "SanityCheck.h"
 

Marlin/example_configurations/makibox/Configuration_adv.h

@@ -653,6 +653,38 @@ const unsigned int dropsegments = 5; //everything with less than this number of
 
 #endif
 
+/**
+ * TWI/I2C BUS
+ *
+ * This feature is an EXPERIMENTAL feature so it shall not be used on production
+ * machines. Enabling this will allow you to send and receive I2C data from slave
+ * devices on the bus.
+ *
+ * ; Example #1
+ * ; This macro send the string "Marlin" to the slave device with address 0x63
+ * ; It uses multiple M155 commands with one B<base 10> arg
+ * M155 A63  ; Target slave address
+ * M155 B77  ; M
+ * M155 B97  ; a
+ * M155 B114 ; r
+ * M155 B108 ; l
+ * M155 B105 ; i
+ * M155 B110 ; n
+ * M155 S1   ; Send the current buffer
+ *
+ * ; Example #2
+ * ; Request 6 bytes from slave device with address 0x63
+ * M156 A63 B5
+ *
+ * ; Example #3
+ * ; Example serial output of a M156 request
+ * echo:i2c-reply: from:63 bytes:5 data:hello
+ */
+
+// @section i2cbus
+
+//#define EXPERIMENTAL_I2CBUS
+
 #include "Conditionals.h"
 #include "SanityCheck.h"
 

Marlin/example_configurations/tvrrug/Round2/Configuration_adv.h

@@ -653,6 +653,38 @@ const unsigned int dropsegments = 5; //everything with less than this number of
 
 #endif
 
+/**
+ * TWI/I2C BUS
+ *
+ * This feature is an EXPERIMENTAL feature so it shall not be used on production
+ * machines. Enabling this will allow you to send and receive I2C data from slave
+ * devices on the bus.
+ *
+ * ; Example #1
+ * ; This macro send the string "Marlin" to the slave device with address 0x63
+ * ; It uses multiple M155 commands with one B<base 10> arg
+ * M155 A63  ; Target slave address
+ * M155 B77  ; M
+ * M155 B97  ; a
+ * M155 B114 ; r
+ * M155 B108 ; l
+ * M155 B105 ; i
+ * M155 B110 ; n
+ * M155 S1   ; Send the current buffer
+ *
+ * ; Example #2
+ * ; Request 6 bytes from slave device with address 0x63
+ * M156 A63 B5
+ *
+ * ; Example #3
+ * ; Example serial output of a M156 request
+ * echo:i2c-reply: from:63 bytes:5 data:hello
+ */
+
+// @section i2cbus
+
+//#define EXPERIMENTAL_I2CBUS
+
 #include "Conditionals.h"
 #include "SanityCheck.h"
 

Marlin/twibus.cpp

@@ -0,0 +1,104 @@
+/*
+ * Marlin 3D Printer Firmware
+ * Copyright (C) 2016 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (C) 2011 Camiel Gubbels / Erik van der Zalm
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#include "Marlin.h"
+
+#if ENABLED(EXPERIMENTAL_I2CBUS)
+
+#include "twibus.h"
+
+#include <Wire.h>
+
+TWIBus::twibus() {
+  Wire.begin(); // We use no address so we will join the BUS as the master
+  this->reset();
+}
+
+void TWIBus::reset() {
+  this->addr = 0;
+  this->buffer_s = 0;
+  this->buffer[0] = 0x00;
+}
+
+void TWIBus::address(uint8_t addr) {
+  this->addr = addr;
+
+  if (DEBUGGING(INFO)) {
+    SERIAL_ECHOPAIR("TWIBus::sendto: ", this->addr);
+    SERIAL_EOL;
+  }
+}
+
+void TWIBus::addbyte(char c) {
+  if (buffer_s >= sizeof(this->buffer)) return;
+  this->buffer[this->buffer_s++] = c;
+
+  if (DEBUGGING(INFO)) {
+    SERIAL_ECHOPAIR("TWIBus::addbyte: ", this->buffer[this->buffer_s -1]);
+    SERIAL_EOL;
+  }
+}
+
+void TWIBus::send() {
+  if (!this->addr) return;
+  if (DEBUGGING(INFO)) SERIAL_ECHOLNPGM("TWIBus::send()");
+
+  Wire.beginTransmission(this->addr);
+  Wire.write(this->buffer, this->buffer_s);
+  Wire.endTransmission();
+
+    // Reset the buffer after sending the data
+  this->reset();
+}
+
+void TWIBus::reqbytes(uint8_t bytes) {
+  if (!this->addr) return;
+  if (DEBUGGING(INFO)) {
+    SERIAL_ECHOPAIR("TWIBus::reqbytes(): ", bytes);
+    SERIAL_EOL;
+  }
+
+  millis_t t = millis();
+  Wire.requestFrom(this->addr, bytes);
+
+    // requestFrom() is a blocking function
+  while (Wire.available() < bytes) {
+    if (millis() - t >= this->timeout) break;
+    else continue;
+  }
+
+  SERIAL_ECHO_START;
+  SERIAL_ECHOPAIR("i2c-reply: from:", this->addr);
+  SERIAL_ECHOPAIR(" bytes:", Wire.available());
+  SERIAL_ECHOPGM (" data:");
+
+    // Protect against buffer overflows if the number of received bytes
+    // is less than the number of requested bytes
+  uint8_t wba = Wire.available();
+  for (int i = 0; i < wba; i++) SERIAL_CHAR(Wire.read());
+  SERIAL_EOL;
+
+  // Reset the buffer after sending the data
+  this->reset();
+}
+
+#endif //EXPERIMENTAL_I2CBUS

Marlin/twibus.h

@@ -0,0 +1,122 @@
+/*
+ * Marlin 3D Printer Firmware
+ * Copyright (C) 2016 MarlinFirmware [https://github.com/MarlinFirmware/Marlin]
+ *
+ * Based on Sprinter and grbl.
+ * Copyright (C) 2011 Camiel Gubbels / Erik van der Zalm
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+#ifndef TWIBUS_H
+#define TWIBUS_H
+
+/**
+ * TWIBUS class
+ *
+ * This class implements a wrapper around the two wire (I2C) bus, it allows
+ * Marlin to send and request data from any slave device on the bus. This is
+ * an experimental feature and it's inner workings as well as public facing
+ * interface are prune to change in the future.
+ *
+ * The two main consumers of this class are M155 and M156, where M155 allows
+ * Marlin to send a I2C packet to a device (please be aware that no repeated
+ * starts are possible), this can be done in caching method by calling multiple
+ * times M155 B<byte-1 value in base 10> or a one liner M155, have a look at
+ * the gcode_M155() function for more information. M156 allows Marlin to
+ * request data from a device, the received data is then relayed into the serial
+ * line for host interpretation.
+ *
+ */
+class TWIBus {
+  private:
+    /**
+     * @brief Timeout value in milliseconds
+     * @details For blocking operations this constant value will set the max
+     * amount of time Marlin will keep waiting for a reply. Useful is something
+     * goes wrong on the bus and the SDA/SCL lines are held up by another device.
+     */
+    const int timeout = 5;
+
+    /**
+     * @brief Target device address
+     * @description This stores, until the buffer is flushed, the target device
+     * address, take not we do follow Arduino 7bit addressing.
+     */
+    uint8_t addr = 0;
+
+    /**
+     * @brief Number of bytes on buffer
+     * @description This var holds the total number of bytes on our buffer
+     * waiting to be flushed to the bus.
+     */
+    uint8_t buffer_s = 0;
+
+    /**
+     * @brief Internal buffer
+     * @details This is a fixed buffer, TWI command cannot be longer than this
+     */
+    char buffer[30];
+
+
+  public:
+    /**
+     * @brief Class constructor
+     * @details Initialized the TWI bus and clears the buffer
+     */
+    TWIBus();
+
+    /**
+     * @brief Reset the buffer
+     * @details Brings the internal buffer to a known-empty state
+     */
+    void reset();
+
+    /**
+     * @brief Send the buffer data to the bus
+     * @details Flushed the buffer into the bus targeting the cached slave device
+     * address.
+     */
+    void send();
+
+    /**
+     * @brief Add one byte to the buffer
+     * @details Adds the byte to the buffer in a sequential way, if buffer is full
+     * the request is silently ignored.
+     *
+     * @param c a data byte
+     */
+    void addbyte(char c);
+
+    /**
+     * @brief Sets the target slave address
+     * @details The target slave address is stored so it can be later used when
+     * the complete packet needs to be sent over the bus.
+     *
+     * @param addr 7-bit integer address
+     */
+    void address(uint8_t addr);
+
+    /**
+     * @brief Request data from slave device
+     * @details Requests data from a slave device, when the data is received it will
+     * be relayed to the serial line using a parser-friendly formatting.
+     *
+     * @param bytes the number of bytes to request
+     */
+    void reqbytes(uint8_t bytes);
+};
+
+#endif //TWIBUS_H