Support for the Arduino Nano board. More...

Detailed Description

Support for the Arduino Nano board.

Overview

The Arduino Nano is the cheapest member of the Arduino family. It is based on Atmel's AVR architecture and sports an ATmega328p MCU. It is like many Arduinos extensible by using shields.

MCU

MCU	ATmega328p
Family	AVR/ATmega
Vendor	Atmel
RAM	2 KiB
Flash	32 KiB (2 KiB reserved for the bootloader)
Frequency	16 MHz
Timers	3 (2x 8bit, 1x 16bit)
ADCs	6 analog input pins
UARTs	1
SPIs	1
I2Cs	1 (called TWI)
Vcc	5.0V
MCU Datasheet	ATmega328p datasheet
Board Manual	Board Manual

Flashing the Device

Flashing RIOT on the Arduino Nano is quite straight forward, just connect your Arduino Nano via the USB connector to your host computer and type:

make BOARD=arduino-nano flash

This should take care of everything!

We use the open avrdude tool to write the new code into the ATmega328p's flash

Using Optiboot

You can use the Optiboot bootloader instead of the stock bootloader for faster programming. Optiboot also is smaller (512 byte instead of 2 KiB), so that 1.5 KiB more program memory is available for RIOT. Refer to the project page for instructions on how to build an flash the bootloader. Don't forgot to also update the fuse settings to set the bootloader size to 256 words (512 bytes).

Compile and flash with make BOARD=arduino-nano BOOTLOADER=optiboot flash or use export ARDUINO_NANO_BOOTLOADER=optiboot in order to not have to specify the bootloader during compilation and flashing.

Issues

RIOT Stuck in Reboot Loop

If RIOT is stuck in a reboot loop e.g. after restarting the device with the reboot shell command, this is likely caused by an issue with the stock bootloader that can be solved by using Optiboot as bootloader instead (see above).

On-Chip Debugging

On-Chip Debugging on the Arduino Nano is not supported via the usual JTAG interface used in ATmega MCUs with higher pin counts, but via debugWIRE. While debugWIRE has the advantage of only using the RESET pin to transfer data, the features provided are extremely limited. If the same issue can be reproduced on an Arduino Mega2560, which supports JTAG, it will be much easier and more productive to debug your code on the Arduino Mega2560. If the bug cannot be reproduced, limited on chip debugging is possible on the Arduino Nano nonetheless.

Prerequisites

Debugging Hardware

In order to be able to use On-Chip Debugging you will need the AVR Dragon, which is the ~~cheapest~~ least expensive programmer and debugger available that supports programming via SPI ("normal ISP"), High Voltage Serial Programming, and Parallel Programming, as well as debugging via JTAG, debugWIRE, PDI and aWire. So at least can use it for just about every AVR device.

Board Modifications

On the Arduino Nano the RESET pin of the MCU is connected to a 100 nF capacitor, which in turn is connected to the DTR pin of the FT232RL USB-UART bridge. This allows the device to be automatically reset when you connected to the board via a serial. This is particularly useful during programming via the bootloader (without external ISP programmer), as avrdude can trigger the reset and, thus, start the bootloader without the user having to press a button.

In order to use on-chip debugging, the capacitor needs however to be disconnected from the reset pin. You can either carefully de-solder it (which allows you to solder it back in after debugging), or just break it off with pinch-nose pliers (which usually destroys the capacitor, making the modification permanent). After this modification, flashing via bootloader requires a manual press on the reset button.

Software

You need to have AVaRICE installed. Some distros have this packaged already. If you need to compile it by hand, go for the latest SVN revision. The latest release cannot be compiled on anything but historic platforms and contains bugs that prevent it from debugging the ATmega328P anyway.

Fuses

In order to use On-Chip Debugging, the DWEN bit in the high fuse needs to be enabled (set to zero). The exact fuse settings for debugging and the default fuse setting are these:

Fuse	Default Setting	Debug Setting
Low Fuse	`0xFF`	`0xFF`
High Fuse	`0xDA`	`0x9A`
Extended Fuse	`0xFD`	`0xFD`

You can enable debugWIRE debugging by running (replace <PROGRAMMER> by the name of your programmer, e.g. dragon_isp in case of the AVR Dragon):

avrdude -p m328p -c <PROGRAMMER> -U hfuse:w:0x9a:m

And disable debugging via:

avrdude -p m328p -c <PROGRAMMER> -U hfuse:w:0xda:m

Note: You can use a different ISP to enable debugging, but disabling it again will only work with the AVR Dragon: The ISP will require the RESET pin to work, but the RESET pin is re-purposed for debugWIRE when debugging is enabled. Recent versions of avrdude will use the debugWIRE interface to temporarily disable debugWIRE and restore the RESET pin's default behavior in order to use the ISP. But this requires a programmer/debugger that can be used as both ISP and debugWIRE debugger using the same connector. So don't enable debugging unless you have an AVR Dragon or another plan on how to disable debugging again.

Debugging

With the AVR Dragon, debugging is as simple as running:

make BOARD=arduino-nano debug

Warning: For flashing the device via ISP, avrdude will temporarily disable debugWIRE. If AVaRICE complains that synchronization with the device is not possible after having it flashed, the device might need a cold boot to enable debugWIRE again.

The memory map of the ELF file does not take the bootloader into account. The author of this text used an ISP to program the Arduino Nano during debugging to avoid any issues. You might want to do the same, e.g. via:

make BOARD=arduino-nano PROGRAMMER=dragon_isp flash

Warning: Flashing via ISP overwrites the bootloader. But you can restore it easily using the ISP. Consult the Arduino documentation on how to restore the bootloader.

Note: If you are using a different debugger than the AVR Dragon, you have to export the AVR_DEBUGDEVICE environment variable to the required flag to pass to AVaRICE, e.g. when using the Atmel-ICE you have to export AVR_DEBUGDEVICE=--edbg. If the debug device is not connected via USB, you also need to export AVR_DEBUGINTERFACE to the correct value.

Caution

Don't expect having a working network stack due to very limited resources.

Files
file	board.h
	Board specific definitions for the Arduino Uno board.