class Encoder():
"""
Abstracts a quadrature encoder to give a tick count.
The count is a signed integer starting at zero. It wraps the count from the
attached timer to give a seamless and continuous tick count. Overflows of
the internal timer counter register should be adequatly handled. If
overflows or weird behaviour occurs around the overflow points, try
increasing Encoder.HYSTERESIS.
Note: Only works on pin pairs 'X1' & 'X2', 'X9' & 'X10', or 'Y1', 'Y2'. The
timer will be automatically selected. Both Timer 2 and 5 work for 'X1' &
'X2', but Timer 5 is preferred because Timer 2 is used for LED PWM but both
can be used by changing the values of Encoder.AF_MAP.
"""
# Constant for decoding in single line mode
SINGLE_MODE = Timer.ENC_A
# Constant for decoding in quad mode
DUAL_MODE = Timer.ENC_AB
# Maps alternate pin function descriptions to the required timer number
TIMER_MAP = {'AF1_TIM2': 2, 'AF2_TIM4': 4, 'AF2_TIM5': 5, 'AF3_TIM8': 8}
# Maps pin names to the alternate function to use
AF_MAP = {
'X1': 'AF2_TIM5',
'X2': 'AF2_TIM5',
'X9': 'AF2_TIM4',
'X10': 'AF2_TIM4',
'Y1': 'AF3_TIM8',
'Y2': 'AF3_TIM8'
}
# Defines the pin pairs that must be used
PIN_PAIRS = [['X1', 'X9', 'Y1'], ['X2', 'X10', 'Y2']]
# Hysteresis value to overflow detection
HYSTERESIS = 12 # One full rotation of encoder
def __init__(self, pinA, pinB, mode=DUAL_MODE):
"""
Instantiate an Encoder object.
Initalises the Pins, Timer and TimerChannel for use as a quadrature
decoder. Registers an overflow callback to elegantly handle counter
register overflows.
pinA: Any valid value taken by pyb.Pin constructor
pinB: Any valid value taken by pyb.Pin constructor
mode: Mode to use for decoding (Encoder.SINGLE_MODE or
Encoder.DUAL_MODE)
raises: Any exception thrown by pyb.Pin, pyb.Timer, pyb.Timer.channel
or Exception if pins are not compatible pairs
"""
self._chA = Pin(pinA)
self._chB = Pin(pinB)
self._ticks = 0
# Check pins are compatible
self._checkPins(pinA, pinB)
# init pins for alternate encoder function
af = self.AF_MAP[self._chA.names()[1]]
channel = self.TIMER_MAP[af]
af = getattr(Pin, af)
self._chA.init(Pin.AF_PP, pull=Pin.PULL_NONE, af=af)
self._chB.init(Pin.AF_PP, pull=Pin.PULL_NONE, af=af)
# init timer
self._timer = Timer(channel, prescaler=0, period=100000)
# init encoder mode
# self._channel = self._timer.channel(1, mode)
self._timer.channel(1, mode)
# setup overflow callback
self._timer.callback(self._overflow)
# init count register to middle of count
self._timer.counter(self._timer.period() // 2)
self._lastRead = self._timer.counter()
def _checkPins(self, pinA, pinB):
"""
Check that two pins can be used for a decoding and are on the same
timer.
"""
try:
if pinA in self.PIN_PAIRS[0]:
if self.PIN_PAIRS[0].index(pinA) != self.PIN_PAIRS[1].index(
pinB):
raise Exception()
elif pinA in self.PIN_PAIRS[1]:
if self.PIN_PAIRS[0].index(pinB) != self.PIN_PAIRS[1].index(
pinA):
raise Exception()
else:
raise Exception()
except:
raise Exception(pinA + ' & ' + pinB + ' are not on the same Timer')
def ticks(self, ticks=None):
"""
Get or set the current tick count.
Ticks is a signed integer.
"""
if ticks is not None: # set ticks to desired value
self._ticks = ticks
else: # retrieve latest count and update internals
count = self._timer.counter()
self._ticks = self._ticks + (count - self._lastRead)
self._lastRead = count
return self._ticks
def _overflow(self, timer):
"""
Timer overflow callback to gracefully handle overflow events. If
weird things are occurring, try increasing the HYSTERESIS value.
"""
count = timer.counter()
if 0 <= count <= self.HYSTERESIS: # overflow
self._ticks = self._ticks + (timer.period() - self._lastRead +
count)
self._lastRead = count
elif (timer.period() -
self.HYSTERESIS) <= count <= timer.period(): # underflow
self._ticks = self._ticks - (self._lastRead + timer.period() -
count)
self._lastRead = count
else: # hysteresis not big enough
#LED(1).on() # turn on inbuilt red led to show error
pass
class Encoder():
"""
Abstracts a quadrature encoder to give a tick count.
The count is a signed integer starting at zero. It wraps the count from the
attached timer to give a seamless and continuous tick count. Overflows of
the internal timer counter register should be adequatly handled. If
overflows or weird behaviour occurs around the overflow points, try
increasing Encoder.HYSTERESIS.
Note: Only works on pin pairs 'X1' & 'X2', 'X9' & 'X10', or 'Y1', 'Y2'. The
timer will be automatically selected. Both Timer 2 and 5 work for 'X1' &
'X2', but Timer 5 is preferred because Timer 2 is used for LED PWM but both
can be used by changing the values of Encoder.AF_MAP.
"""
# Constant for decoding in single line mode
SINGLE_MODE = Timer.ENC_A
# Constant for decoding in quad mode
DUAL_MODE = Timer.ENC_AB
# Maps alternate pin function descriptions to the required timer number
TIMER_MAP = {'AF1_TIM2': 2, 'AF2_TIM4': 4, 'AF2_TIM5': 5, 'AF3_TIM8': 8}
# Maps pin names to the alternate function to use
AF_MAP = {'X1' : 'AF2_TIM5', 'X2': 'AF2_TIM5', 'X9': 'AF2_TIM4',
'X10': 'AF2_TIM4', 'Y1': 'AF3_TIM8', 'Y2': 'AF3_TIM8'}
# Defines the pin pairs that must be used
PIN_PAIRS = [['X1','X9','Y1'],['X2','X10','Y2']]
# Hysteresis value to overflow detection
HYSTERESIS = 12 # One full rotation of encoder
def __init__(self, pinA, pinB, mode = DUAL_MODE):
"""
Instantiate an Encoder object.
Initalises the Pins, Timer and TimerChannel for use as a quadrature
decoder. Registers an overflow callback to elegantly handle counter
register overflows.
pinA: Any valid value taken by pyb.Pin constructor
pinB: Any valid value taken by pyb.Pin constructor
mode: Mode to use for decoding (Encoder.SINGLE_MODE or
Encoder.DUAL_MODE)
raises: Any exception thrown by pyb.Pin, pyb.Timer, pyb.Timer.channel
or Exception if pins are not compatible pairs
"""
self._chA = Pin(pinA)
self._chB = Pin(pinB)
self._ticks = 0
# Check pins are compatible
self._checkPins(pinA, pinB)
# init pins for alternate encoder function
af = self.AF_MAP[self._chA.names()[1]]
channel = self.TIMER_MAP[af]
af = getattr(Pin, af)
self._chA.init(Pin.AF_PP, pull = Pin.PULL_NONE, af = af)
self._chB.init(Pin.AF_PP, pull = Pin.PULL_NONE, af = af)
# init timer
self._timer = Timer(channel, prescaler = 0, period = 100000)
# init encoder mode
# self._channel = self._timer.channel(1, mode)
self._timer.channel(1, mode)
# setup overflow callback
self._timer.callback(self._overflow)
# init count register to middle of count
self._timer.counter(self._timer.period()//2)
self._lastRead = self._timer.counter()
def _checkPins(self, pinA, pinB):
"""
Check that two pins can be used for a decoding and are on the same
timer.
"""
try:
if pinA in self.PIN_PAIRS[0]:
if self.PIN_PAIRS[0].index(pinA) != self.PIN_PAIRS[1].index(pinB):
raise Exception()
elif pinA in self.PIN_PAIRS[1]:
if self.PIN_PAIRS[0].index(pinB) != self.PIN_PAIRS[1].index(pinA):
raise Exception()
else:
raise Exception()
except:
raise Exception(pinA + ' & ' + pinB + ' are not on the same Timer')
def ticks(self, ticks = None):
"""
Get or set the current tick count.
Ticks is a signed integer.
"""
if ticks is not None: # set ticks to desired value
self._ticks = ticks
else: # retrieve latest count and update internals
count = self._timer.counter()
self._ticks = self._ticks + (count - self._lastRead)
self._lastRead = count
return self._ticks
def _overflow(self, timer):
"""
Timer overflow callback to gracefully handle overflow events. If
weird things are occurring, try increasing the HYSTERESIS value.
"""
count = timer.counter()
if 0 <= count <= self.HYSTERESIS: # overflow
self._ticks = self._ticks + (timer.period() - self._lastRead + count)
self._lastRead = count
elif (timer.period() - self.HYSTERESIS) <= count <= timer.period(): # underflow
self._ticks = self._ticks - (self._lastRead + timer.period() - count)
self._lastRead = count
else: # hysteresis not big enough
#LED(1).on() # turn on inbuilt red led to show error
pass
