Clojure Robots

Name

Kevin Downey

Employer

Sonian, Inc.

Position

Clojure Programmer

(Backend Developer)

Contact

irc hiredman

twitter @hiredman_

http://github.com/hiredman

Beagle Bone

• from Texas Instruments
• Very available (unlike the Pi)
• Last generation board (slower cpu)
• Lots of IO options
• Established extension system (capes)
• Part of a family of boards
• These boards have been in use for several years
• http://beagleboard.org/
• available from amazon for about $80

Interfacing With Hardware

• GPIO pins and AIN pins
• AIN pins are analog in, reads voltages
• GPIO is general purpose digital i/o
• digital i/o means the pin is high or low
• most linux distributions provide access to pins via the fs
• and pins mux

PyBBIO

• Arduino like programming for the bone
• written in Python
• uses mmap to map /dev/mem to fiddle pins "directly"
• knows the magic constants

mmap

• OMG complected
• does a lot of things
• in this case we just want to map a "file" in to memory

mmap for the JVM

• NIO has support for mapping a file into memory as a ByteBuffer
• explodes on fake zero length files like /dev/mem

Some C Code

          JNIEXPORT jlong JNICALL Java_a_B_mem
          (JNIEnv * env, jobject obj, jlong off, jlong size) {

              int fd = open("/dev/mem", O_RDWR|O_SYNC);
              return (long)mmap(NULL, size, PROT_READ |
                                PROT_WRITE, MAP_SHARED, fd, off);

          }
        

sun.misc.Unsafe

• allows for unsafe memory access

JVM

• Oracle has released a jdk port for soft float arm linux
• Beagle Bone is soft float
• newer SOCs often support hard float
• hopefully a hard float arm jdk surfaces soon

Misc

• H-bridge
• power supply
• motors separate ps from board
• usb hubs
• sensors