Additional Servos on the XBC
Wed, 02/02/2011 - 14:08
Has anyone hacked the XBC for extra servo ports? Apparently the Xport can support a lot more servos, the question is what ports are available and what needs to be changed in the firmware to access them.
I plan to hack a few extras in, but if it's already been done I'd rather not waste a bunch of time figuring it out on my own.
-Dan
Have not heard of any hacks like that.
I have a polulu serial to servo board that can be used easily with the serial port. Software wise it is just sending bytes with serial_write_byte();
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Any GPIO port could probably be used as an RC servo port using the GBA's timing interrupts. Implementing them on the FPGA logic wouldn't be as easy, because the XBC's bitstream uses almost all of the available gates. If you really wanted FPGA servos, you could try removing the camera logic (but seeing as the camera is the XBC's flagship feature, that might invalidate its usefulness).
If you're able to rig up the GBA's timing interrupts to handle RC servos, please post here with your results. I will warn you that Direct Sound Channel A uses timers 0 and 1, while Channel B uses 2, 3, and I think either 0 or 1 also (can't remember which). Main lesson, only use Direct Sound Channel A, and restrict your servo code to using timers 2 and 3.
-Jeremy Rand
Senior Programmer, Team SNARC (2012-2013), Norman Advanced (2010-2011), Norman HS (2008-2009), Norman North (2005-2007), Whittier MS (2003-2004)
2012-2013 VP of Tech, 2011 President, Botball YAC (2009-2013)
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I never quite understood the reasoning for 4 motor ports on differential robots. I think if it's possible, I'll do like I did with the Sumo11 and drop two motors to gain more servos. I'm sure it'll be a lot different with the XBC than the 68hc11, but I won't know until I dig in.
-Dan