bacnet_stack/ports/atmega328

BACnet MS/TP on Arduino Uno R3 Platform - Atmega328p

The Arduino Uno R3 platform for this example uses the following peripherals:

1. USB bootloader using AVR-119 protocol

2. 7-position DIP switch for MS/TP MAC address

3. Arduino Uno V3 compatible RS485 shield (DFR0259)

Arduino Uno V3 Pin Mapping

ATmega328p	Arduino	RS485 DFR0259	BACnet Object
NC	NC
+5V	IOREF
RESET	RESET	RST BUTTON
+3V3	+3V3
+5V	+5V	+5V
GND	GND	GND
GND	GND	GND
VIN	VIN
ADC0/PC0	A0		AV 0 Millivolts
ADC1/PC1	A1		AV 1 Millivolts
ADC2/PC2	A2		AV 2 Millivolts
ADC3/PC3	A3		AV 3 Millivolts
ADC4/PC4	A4*
ADC5/PC5	A5*
ADC5/PC5	SCL*	I2C
ADC4/PC4	SDA*	I2C
AVDD	AREF
GND	GND
SCK/PB5	D13	LED-L ANODE (+)	BV 99 (output)
MISO/PB4	D12		BV 9 (output)
MOSI/PB3	D11		BV 8 (output)
SS/PB2	D10		BV 7 (output)
OC1/PB1	D9		BV 6 (output)
ICP/PB0	D8		BV 5 (output)
AIN1/PD7	D7		BV 4 (input)
AIN0/PD6	D6		BV 3 (input)
T1/PD5	D5		BV 2 (input)
T0/PD4	D4		BV 1 (input)
INT1/PD3	D3		BV 0 (input)
INT0/PD2	D2	CE DE /RE RTS	RS485
TXD/PD1	D1/Tx**	TXD	RS485
RXD/PD0	D0/Rx**	RXD	RS485

* ADC4/PC4: A4 and SDA are shared I/O

* ADC5/PC5: A5 and SCL are shared I/O

** shared with Uno R3 USB Tx/Rx. DFR0259 switch ON to disable.

Building this Project

GNU Makefile

There is a GNU Makefile that uses avr-gcc and avr-libc to build the project. avrdude can be used to program the Arduino Uno R3 board via USB.

The GNU Makefile is used in the continuous integration pipeline to validate the build is not broken. The Makefile is called from an Ubuntu image container after installing the necessary tools:

sudo apt-get update -qq
sudo apt-get install -qq build-essential
sudo apt-get install -qq gcc-avr avr-libc binutils-avr avrdude

To add the build and debug tools to MinGW64 environment:

pacman --noconfirm -S mingw-w64-x86_64-gcc-avr
pacman --noconfirm -S mingw-w64-x86_64-avr-libc
pacman --noconfirm -S mingw-w64-x86_64-binutils-avr
pacman --noconfirm -S mingw-w64-x86_64-avrdude

The build sequence is usually:

make clean all

The Makefile includes a recipe to use avrdude to program the Uno R3 via USB

make install

GCC and CStack Usage

CStack check for GCC is included in the device object as property 512. The compile shows 352 (.bss) + 136 (.data) = 488 bytes of RAM used, and the ATmega328 has 2048 bytes of RAM, leaving 1560 bytes for the CStack. BACnet Device object proprietary property 512 is mapped to the CStack Size and returns 1376 using ReadProperty request. After some ReadProperty and WriteProperty requests, the CStack shows 1159 CStack bytes free. Note that the value 0xC5 (197) was used to paint the CStack. Keep this in mind when developing.

Shield option

The DFR0259 shield for RS485 was used, but any RS485 circuit could be attached to the Arduino Uno R3 using the same pins for Tx, Rx, CE RE/DE RTS.

A 7-position DIP switch was connected to GPIO for the MS/TP MAC address, but the value could also be stored in EEPROM.

BACnet Capabilities

The BACnet Capabilities include WhoIs, I-Am, ReadProperty, and WriteProperty support. The BACnet objects include a Device object, 10 Binary Value objects, and 10 Analog Value objects. An GPIO output is controlled by Binary Value object instance 0. All required object properties can be retrieved using ReadProperty. The Present_Value property of the Analog Value and Binary Value objects can be written using WriteProperty. The Object_Identifier, Object_Name, Max_Info_Frames, Max_Master, and baud rate (property 9600) of the Device object can be written using WriteProperty.