match the latest core code

Author: jepler

examples/pioasm_neopixel.py

@@ -8,19 +8,22 @@
 import microcontroller
 import adafruit_pioasm
 
-# NeoPixels are 800khz bit streams. Zeroes are 1/3 duty cycle (~416ns) and ones
-# are 2/3 duty cycle (~833ns).
+# NeoPixels are 800khz bit streams. We are choosing zeros as <312ns hi, 936 lo> and ones
+# and ones as <700 ns hi, 556 ns lo>.
+# cycle. The first two instructions always run while only one of the two final
+# instructions run per bit. We start with the low period because it can be
+# longer while waiting for more data.
 program = """
 .program ws2812
 .side_set 1
 .wrap_target
 bitloop:
-  out x 1        side 0 [1]; Side-set still takes place when instruction stalls
-  jmp !x do_zero side 1 [1]; Branch on the bit we shifted out. Positive pulse
-do_one:
-  jmp  bitloop   side 1 [1]; Continue driving high, for a long pulse
-do_zero:
-  nop            side 0 [1]; Or drive low, for a short pulse
+   out x 1        side 0 [6]; Drive low. Side-set still takes place before instruction stalls.
+   jmp !x do_zero side 1 [3]; Branch on the bit we shifted out previous delay. Drive high.
+ do_one:
+   jmp  bitloop   side 1 [4]; Continue driving high, for a one (long pulse)
+ do_zero:
+   nop            side 0 [4]; Or drive low, for a zero (short pulse)
 .wrap
 """
 
@@ -35,7 +38,7 @@
 
 sm = rp2pio.StateMachine(
     assembled,
-    frequency=800000 * 6,  # 800khz * 6 clocks per bit
+    frequency=12_800_000,  # to get appropriate sub-bit times in PIO program
     first_sideset_pin=NEOPIXEL,
     auto_pull=True,
     out_shift_right=False,