Change a couple of PIO examples to run at 2000Hz

Fixes raspberrypi#18

Author: lurch

pio/pio_blink.py

@@ -19,10 +19,10 @@ def blink():
     nop()          [31]
     wrap()
 
-# Instantiate a state machine with the blink program, at 1000Hz, with set bound to Pin(25) (LED on the rp2 board)
-sm = rp2.StateMachine(0, blink, freq=1000, set_base=Pin(25))
+# Instantiate a state machine with the blink program, at 2000Hz, with set bound to Pin(25) (LED on the rp2 board)
+sm = rp2.StateMachine(0, blink, freq=2000, set_base=Pin(25))
 
 # Run the state machine for 3 seconds.  The LED should blink.
 sm.active(1)
 time.sleep(3)
-sm.active(0)
+sm.active(0)

pio/pio_irq.py

@@ -19,7 +19,7 @@ def irq_test():
 
 rp2.PIO(0).irq(lambda pio: print(pio.irq().flags()))
 
-sm = rp2.StateMachine(0, irq_test, freq=1000)
+sm = rp2.StateMachine(0, irq_test, freq=2000)
 sm.active(1)
 time.sleep(1)
-sm.active(0)
+sm.active(0)