add test for issue #170

Output from running test:

debian@beaglebone:~/ssh/adafruit-beaglebone-io-python$ sudo python test/issue170-pwm.py; journalctl -p debug -t python --since "1 min ago"
-- Logs begin at Tue 2017-10-31 06:56:00 UTC, end at Tue 2017-10-31 07:36:39 UTC. --
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: version <unknown> initialized
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: pwm_start: P9_14, 50.000000, 2000.000000, 1
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: lookup_exported_pwm: couldn't find 'P9_14'
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: initialize_pwm: OK
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: set_pin_mode() :: Pinmux file /sys/devices/platform/ocp/ocp:P9_14
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: set_pin_mode() :: Set pinmux mode to pwm for P9_14
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: pwm_start: P9_14, /sys/devices/platform/ocp/48302000.epwmss/48302
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: pwm_start: P9_14, /sys/devices/platform/ocp/48302000.epwmss/48302
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: pwm_setup: P9_14 OK
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: pwm_start: call pwm_set_frequency(key=P9_14 freq=2000.000000)
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: pwm_set_frequency: P9_14 2000.000000 OK
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: pwm_start: call pwm_set_duty_cycle(key=P9_14 duty=50.000000)
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: pwm_set_duty_cycle: P9_14 50.000000 OK
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: pwm_start: call pwm_set_polarity(key=P9_14 polarity=1)
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: pwm_set_polarity: P9_14 1 OK
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: pwm_start: write(pwm->enable_fd, buffer=1, len=1)
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: pwm_start: P9_14 OK
Oct 31 07:35:57 beaglebone python[1997]: [40B blob data]
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: pwm_start: P9_14, 50.000000, 2000.000000, 0
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: lookup_exported_pwm: couldn't find 'P9_14'
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: set_pin_mode() :: Pinmux file /sys/devices/platform/ocp/ocp:P9_14
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: set_pin_mode() :: Set pinmux mode to pwm for P9_14
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: pwm_start: P9_14, /sys/devices/platform/ocp/48302000.epwmss/48302
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: pwm_start: P9_14, /sys/devices/platform/ocp/48302000.epwmss/48302
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: pwm_setup: P9_14 OK
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: pwm_start: call pwm_set_frequency(key=P9_14 freq=2000.000000)
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: pwm_set_frequency: P9_14 2000.000000 OK
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: pwm_start: call pwm_set_duty_cycle(key=P9_14 duty=50.000000)
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: pwm_set_duty_cycle: P9_14 50.000000 OK
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: pwm_start: call pwm_set_polarity(key=P9_14 polarity=0)
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: pwm_set_polarity: P9_14 0 OK
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: pwm_start: write(pwm->enable_fd, buffer=1, len=1)
Oct 31 07:35:57 beaglebone python[1997]: Adafruit_BBIO: pwm_start: P9_14 OK
Oct 31 07:35:57 beaglebone python[1997]: [40B blob data]

Author: pdp7

test/issue170-pwm.py

@@ -0,0 +1,5 @@
+import Adafruit_BBIO.PWM as PWM
+PWM.start("P9_14", 50, 2000, 1)
+PWM.cleanup()
+PWM.start("P9_14", 50, 2000, 0)
+PWM.cleanup()