I thought I remembered answering this post from four months ago…
Massi, you could use a Baby-O programmed as a serial coprocessor. That would get you it’s two motor driver channels and I/Os. Anything with a serial port can be controlled with a USB-Serial chip. Also remember that the Raspberry Pi has UART and SPI/I2C pins, though they are 3.3V.
I have no ties to AVR or 8bit. I actually dislike AVRs for many reasons. As far as microcontroller companies go, I actually like Microchip PICs the best. It helps that I’ve been working with them the longest though. PICs (at least 8bit) lack a open source and (non-handicapped) free compiler though.
I tend to switch between two (maybe more) mindsets when looking at microcontroller boards. One mindset puts ease of use and cost at the forefront. This is why I like Arduino and similar (lower case arduinos). Download one zipped folder, unpack, install one driver and you are done and ready to start programming on the software side. Libraries are basically drop and go. I also sometimes get into power freak mode, where I look for the most powerful hardware, with less focus on cost, and slightly less focus on ease of use. This is when I look at things like the Leaflabs boards, Chipkit, Raspberry Pi, 16bit PICs, etc.
Baby-Os satisfy price, but general ease of use just isn’t as good as arduinos. Arduinos in general are easier to use, but all or nearly all lack an onboard motor driver, making the hardware slightly more complex.
I would see a $20-22 mega328 based arduino with onboard USB and motor drivers as a very good value. I also don’t see it being a bad value for the company making it, since PJRC makes money off of Teensys at $16, with no motor driver.
It would be great to have some more 32bit robot controllers on the market, especially if they don’t cost an arm and a leg (yeah, I’m looking at you VEX).
For libraries and core code, you could start with Leaflabs STM32 cores. Their philosophy is to largely stick with similar programming as Arduino, but be willing to break compatibility for the sake of fully utilizing the hardware.
I’d like to see a one shot download of Eclipse setup for programming arduinos, Orangs and other controller boards. It’s a very nice step up once you get past the stage where a very simple IDE (like Processing/Arduino) is needed. Here is their license.