C&C: The Wimpy Robot Bumper Class

25 Jun 2016

Here is the Bumper Class with polling thread to read the bumpers asynchronously from the consumer (test main() in the same file) and my control-c handler that can call a class object's cancel function to kill the thread and clean up: (I have the feeling I don't need the global statements.)

[code]
#
# myPyLib.py SUPPLIMENTAL PYTHON FUNCTIONS
#
# v0.1 19June2016

import time
import sys
import signal

# ######### CNTL-C #####
# Callback and setup to catch control-C and quit program

_funcToRun=None

def signal_handler(signal, frame):
print '\n** Control-C Detected'
if (_funcToRun != None):
_funcToRun()
sys.exit(0)

# Setup the callback to catch control-C
def set_cntl_c_handler(toRun):
global _funcToRun
_funcToRun = toRun
signal.signal(signal.SIGINT, signal_handler)
[/code]

[code]
#!/usr/bin/python
#
# bumbersClass.py   BUMPERS SENSOR CLASS
#

import PDALib
import myPDALib
import myPyLib
import time
import sys
import threading

class Bumpers():

# CLASS VARS (Avail to all instances)
# Access as Bumpers.class_var_name

pollThreadHandle=None   # the SINGLE read sensor thread for the Bumpers class
tSleep=0.033            # time for read_sensor thread to sleep after each read op

# Bumpers are on the Pi Droid Alpha MCP23S17 DIO expander
# Wired to use internal pull-up power of the MCP23S17
# Bumper value is negative logic - 0 means bumper activated, normal 1

LeftBumperDIO=18
RightBumperDIO=17
RearBumperDIO=16

# Allowable Bumpers.state values
NONE     = 0
# Single bumpers
LEFT     = 1
RIGHT    = 2
REAR     = 4
# Combinations
FRONT    = 3
LEFTREAR = 5
RIGHTREAR= 6
ALL      = 7
# Not possible
UNKNOWN = 8

# THE STATE OF EACH BUMPER and the combined BUMPERS state
# (class vars because there are only one physical bumper)
# note: can get rid of left(), right(), rear() methods by using these vars direct
leftState= UNKNOWN
rightState=UNKNOWN
rearState= UNKNOWN
state=     UNKNOWN #0,1=L,2=R,3=L+R(front),4=Rear,...

# use to print Bumper.state var
bumperStrings=["NONE", "LEFT", "RIGHT", "FRONT", "REAR",
               "LEFTREAR", "RIGHTREAR", "ALL", "UNKNOWN"]

# end of class vars definition

def __init__(self):
    # SINGLETON TEST
    if (Bumpers.pollThreadHandle!=None):
        print "Second Bumpers Class Object, not starting pollingThread"
        return None

    # Set Bumper DIO channels as input for now
    PDALib.pinMode(Bumpers.LeftBumperDIO, PDALib.INPUT)
    PDALib.pinMode(Bumpers.RightBumperDIO,PDALib.INPUT)
    PDALib.pinMode(Bumpers.RearBumperDIO, PDALib.INPUT)

    # Set internal pull-ups on bumper channels
    PDALib.setDioBit( PDALib.DIO_GPPU, 8 ) # set LeftBumper pin 16 pull-up
    PDALib.setDioBit( PDALib.DIO_GPPU, 9 ) # set RightBumper pin 17 pull-up
    PDALib.setDioBit( PDALib.DIO_GPPU, 10 ) # set RearBumper pin 18 pull-up
    # threading target must be an instance
    Bumpers.pollThreadHandle = threading.Thread( target=self.pollBumpers,
                                               args=(Bumpers.tSleep,))
    Bumpers.pollThreadHandle.start()
#end init()

# BUMPER THREAD WORKER METHOD TO READ BUMPERS
def pollBumpers(self,tSleep=0.01):
    print "pollBumpers started with %f" % tSleep
    t = threading.currentThread()   # get handle to self (pollingBumpers thread)
    while getattr(t, "dorun", True): # check the dorun thread attribute
      self.read()
      time.sleep(tSleep)
    print("dorun went false. Stopping pollBumpers thread")


def read(self): #READ THE BUMPERS - can be used as poll or directly
      Bumpers.leftState= Bumpers.LEFT - Bumpers.LEFT * \
     PDALib.digitalRead(Bumpers.LeftBumperDIO)
      Bumpers.rightState= Bumpers.RIGHT - Bumpers.RIGHT * \
       PDALib.digitalRead(Bumpers.RightBumperDIO)
      Bumpers.rearState= Bumpers.REAR - Bumpers.REAR * \
    PDALib.digitalRead(Bumpers.RearBumperDIO)
      Bumpers.state = Bumpers.leftState + Bumpers.rightState + Bumpers.rearState
      return Bumpers.state

def status(self):
    return Bumpers.state

def left(self):
    return Bumpers.leftState

def right(self):
    return Bumpers.rightState

def rear(self):
    return Bumpers.rearState

def toString(self,bumperState=UNKNOWN):
    if (bumperState==Bumpers.UNKNOWN):
       bumperState= Bumpers.state
    return Bumpers.bumperStrings[bumperState]

def cancel(self):
     print "bumpers.cancel() called"
     self.pollThreadHandle.dorun = False
     myPDALib.PiExit()

# ##### BUMPER CLASS TEST METHOD ######
# creates two instances, only the first should start the read() thread
# the first time through the main() while loop, the sensors may not have been read yet
#     so bumpers.status() and each bumper may have a value of 8/UNKNOWN
def main():
# note: lowercase bumpers is object, uppercase Bumpers is class (everywhere in code)
bumpers=Bumpers() #create an instance which starts the read bumpers thread
bumpersNoThreadStart=Bumpers() # Test a second instance of class
myPyLib.set_cntl_c_handler(bumpers.cancel) # Set CNTL-C handler
while True:
      print "\n"
      print "bumpers.state: %d %s" % (bumpers.status(), bumpers.toString())
      print "left():%d rear():%d right():%d" % (
bumpers.left(),
bumpers.rear(),
bumpers.right() )
      time.sleep(1)
#end while

if __name__ == "__main__":
    main()

[/code]