TNC2 Firmware

Building the Firmware

To build the software, just type "make". This will create a file called images/mobilinkd-tnc1.elf

The EEPROM section needs to be removed from the ihex file.

$ avr-objcopy -O ihex -R.eeprom images/mobilinkd-tnc1.elf images/mobilinkd-tnc1.hex

The hex file can then be uploaded using avrdude -c avr109 or using the Mobilinkd Android configuration app. When using avrdude enter the bootloader by holding down the power button and pressing the reset button. The TNC will enter the bootloader. You have 8 seconds to start the upload.

$ avrdude -c avr109 -p m328p -P /dev/rfcomm0 -U images/mobilinkd-tnc1.hex

If the bootloader has not been activated within 8 seconds, the TNC resets.

See below for setting up the Bluetooth serial port on Linux.

Bootloader

The Mobilinkd TNC2 uses the XBoot++ bootloader: https://github.com/alexforencich/xboot

The configuration file for the bootloader is in the xboot subdirectory. An existing xboot.hex image is in the images/ directory.

To build an image which includes the bootloader, either use the supplied bootloader image or build the xboot++ bootloader using the supplied xboot configuration file. Then merge the two files with srec_cat.

$ cd images
$ srec_cat xboot.hex -intel mobilinkd-tnc1.hex -intel -o mobilinkd-boot.hex -intel

The output file, mobilinkd-boot.hex, can then be uploaded via the ISP port on the board using an ISP programmer such as the USBASP v2.0. This is the programmer that I use, along with a custom cable with pogo pins.

$ avrdude -p m328pb -c usbasp -v -U mobilinkd-boot.hex

If you are creating your own version of the board, you will need to set the fuses on the TNC before flashing the image.

Fuses

The MCU fuses must be set as follows:

lfuse: 0xFF
hfuse: 0xD2
efuse: 0x05

$ avrdude -p m328pb -c usbasp -v -B 40 -U lfuse:w:0xFF:m -U hfuse:w:0xD2:m -U efuse:w:0x05:m

The lock bit (set after the firmware with bootloader is written) should be set to:

lock: 0x2F

$ avrdude -p m328pb -c usbasp -v -B 40 -U lock:w:0x2F:m 

Configuring a Bluetooth Serial Port on Linux

This section assumes some familiarity with working with Bluetooth devices on Linux. At a minimum, you need to know how to pair a device with your system.

The first thing to do is to pair the Bluetooth device. This is best done via the Bluetooth Setting applet. Once paired, you will need the MAC address of the TNC. Otherwise you can use the bluetoothctl program interactively from the command line.

$ bluetoothctl
Agent registered
[NEW] Device 20:16:11:15:20:34 Mobilinkd TNC2
# pair 20:16:11:15:20:34
Attempting to pair with 20:16:11:15:20:34
[CHG] Device 20:16:11:15:20:34 Connected: yes
Request PIN code
[agent] Enter PIN code: 1234
[CHG] Device 20:16:11:15:20:34 UUIDs: 00001101-0000-1000-8000-00805f9b34fb
[CHG] Device 20:16:11:15:20:34 ServicesResolved: yes
[CHG] Device 20:16:11:15:20:34 Paired: yes
Pairing successful
[CHG] Device 20:16:11:15:20:34 ServicesResolved: no
[CHG] Device 20:16:11:15:20:34 Connected: no
[CHG] Device 20:16:11:15:20:34 RSSI: -58
# quit
...
$

Set up the serial port with:

$ sudo rfcomm bind 0 <MAC ADDRESS> 1

For example, using the MAC address above:

$ sudo rfcomm bind 0 20:16:11:15:20:34 1

This will create the device /dev/rfcomm0.

When done using this device, before turning off then TNC, unbind the port.

$ sudo rfcomm unbind 0