boards/arduino-nano: Refactor avrdude conf

- Use the common logic to translate from a bootloader to concrete flasher flags
- Extended documentation on how to use optiboot as alternative bootloader, as
  the stock bootloader is affected by a bug preventing the use of RIOT's
  pm_reboot() implementation

boards/arduino-nano/Makefile.include

@@ -3,18 +3,7 @@ PORT_LINUX  ?= /dev/ttyUSB0
 PORT_DARWIN ?= $(firstword $(sort $(wildcard /dev/tty.usbmodem*)))
 BAUD        ?= 9600
 
-PROGRAMMER ?= arduino
-
-ifeq (arduino,$(PROGRAMMER))
-  # the Arduino Nano bootloader is 2KiB in size
-  BOOTLOADER_SIZE ?= 2048
-  # the Nano's bootloader uses 57600 baud for programming
-  FFLAGS_EXTRA += -b 57600
-else
-  # not using the bootloader for programming, thus the whole flash can be used
-  BOOTLOADER_SIZE ?= 0
-endif
-
-ROM_RESERVED ?= $(BOOTLOADER_SIZE)
+ARDUINO_NANO_BOOTLOADER ?= atmegaboot
+BOOTLOADER ?= $(ARDUINO_NANO_BOOTLOADER)
 
 include $(RIOTBOARD)/common/arduino-atmega/Makefile.include

boards/arduino-nano/doc.txt

@@ -26,7 +26,7 @@ extensible by using shields.
 | MCU Datasheet | [ATmega328p datasheet](http://ww1.microchip.com/downloads/en/DeviceDoc/ATmega48A-PA-88A-PA-168A-PA-328-P-DS-DS40002061A.pdf) |
 | Board Manual  | [Board Manual](https://www.arduino.cc/en/uploads/Main/ArduinoNanoManual23.pdf) |
 
-## Flashing the device
+## 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:
 
@@ -37,6 +37,28 @@ This should take care of everything!
 We use the open `avrdude` tool to write the new code into the ATmega328p's
 flash
 
-##Caution
+## Using Optiboot
+
+You can use the [Optiboot](https://github.com/Optiboot/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](https://forum.arduino.cc/index.php?topic=150419.0)
+that can be solved by using Optiboot as bootloader instead (see above).
+
+## Caution
 Don't expect having a working network stack due to very limited resources.
  */