Some may ask, why I have chosen the XMEGA32E5 for the project. Here is why, or at least why at the end I used it.
Why the XMEGA?
Arduino is a great starting point for microcontroller beginners. Its widely available, has boards for easy assembling, a nice IDE and libraries for abstraction. And it’s all open source and low priced. So I started with the ATMEGA family going to straight AVR GCC programming using an ATTINY. Seeing Schorsch’s project on the RC-Heli thread using the XMEGA with some features got my attention. The upgrade from the ATMEGA shouldn’t be that difficult.
ATMEGA vs. XMEGA
The XMEGA32E5 comes in a small TQFP package. I was looking for a SMD package, since it reduces the overall project footprint. It brings a 12 Bit Analog-Digital-Converter and a event-system. There are two I2C ports, one as an I2C Slave and one as an I2C Master. The slave port is used for the connection to the Spektrum-RC, the master port for the BMP180 pressure sensor. The XMEGA has a 32MHz clock rate compared to the 16MHz of the ATMEGA328.
Being quite new to micros I didn’t expect much differences. But there are some. First, the XMEGA uses 3.3V and can not be operated using 5V. So all components should work with 3.3V too. Next the XMEGA uses PDI instead of ISP for programming the device. So I needed a dedicated programmer, since the Bootloader/USB method of the Arduino doesn’t work. I used the Arduino as an ISP for the ATTINY, which doesn’t work as well. Eventually I got a small cheap AVRISP clone based on an Atmel chip. But the Jungo USB drivers are not compatible to the Mac. So I switched to Windows, the Atmel AVR Studio and the ASF a development framework. To test this it is handy to have a XMEGA breakout board for testing.
Some words on developing on Mac OsX
Using a Mac is no problem in most cases. A lot of Linux software is easily usable. There is a AVR GCC toolchain and avrdude version at the Atmel website. Using a programmer with the FTDI USB chip (like the Arduinos use) is also no problem. But both, the cheap AVR ISP mkII clone as well as an Atmel JTAG ICE mkII didn’t work with Mac OsX, since there is no Mac driver for the used Atmel USB chip. And I couldn’t get the libusb running. At the end I switched to Windows 8.1 in a Parallels VM. With this I use the AVR Studio 6.x. This is not that fast on my Mac Book Air (2010), but works. I like the GCC toolchain, because it’s lightweight, but the AVR Studio is much more easy to use.
Using the Atmel AVR Studio and ASF
The AVR Studio and ASF makes it easy to setup the device specific parts of a project. Just select the microcontroller and modules (like ADC, Timer, etc.) used in the project, the programming tool and board if using a standard Atmel board. The IDE and ASF takes care of including the required libraries and tools. The ASF works, but not always as expected. Maybe I will write on this later on.
The change from the ATMEGA to XMEGA was quite painful, since I changed the complete development tool chain. This was the case, since I use a Mac and the programmer hardware does not supporte Mac OsX.
Beside this it is quite different to program using Arduino, the Atmel AFS or pure C. I didn’t test the XMEGA Arduino port, but I will keep using Arduino for fast prototyping with the ATMEGA. At the moment I will stay with the AVR Studio and AFS for the more complex projects.Share