From 564fafd6d5be604e7edbd6b2914f93986105ec89 Mon Sep 17 00:00:00 2001
From: Sandor Attila Gerendi <sanyi@users.noreply.github.com>
Date: Sat, 13 Feb 2021 21:14:11 +0200
Subject: [PATCH 1/3] Create pio_quadrature_encoder.py

Example that is using StateMachine to offload quadrature encoder pooling.
---
 examples/rp2/pio_quadrature_encoder.py | 99 ++++++++++++++++++++++++++
 1 file changed, 99 insertions(+)
 create mode 100644 examples/rp2/pio_quadrature_encoder.py

diff --git a/examples/rp2/pio_quadrature_encoder.py b/examples/rp2/pio_quadrature_encoder.py
new file mode 100644
index 0000000000..2fa38e8a12
--- /dev/null
+++ b/examples/rp2/pio_quadrature_encoder.py
@@ -0,0 +1,99 @@
+"""
+This implementation offloads the quadrature sensor continuous pooling to the StateMachine pio_quadrature,
+pio_quadrature will detect state changes and push the values then raises an interrupt that is handled by
+encoder_state_changed_irq_handler
+
+encoder_state_changed_irq_handler was inspired from 
+https://electronics.stackexchange.com/questions/360637/quadrature-encoder-most-efficient-software-implementation
+
+"""
+
+from machine import Pin
+from rp2 import PIO, StateMachine
+import utime
+import array
+
+
+state_look_up_table = array.array("b", [
+        #Direction = 1
+        0, # 00 to 00
+       -1, # 00 to 01
+       +1, # 00 to 10
+       +2, # 00 to 11
+
+       +1, # 01 to 00
+        0, # 01 to 01
+       +2, # 01 to 10
+       -1, # 01 to 11
+
+       -1, # 10 to 00
+       +2, # 10 to 01
+        0, # 10 to 10
+       +1, # 10 to 11
+
+       +2, # 11 to 00
+       +1, # 11 to 01
+       -1, # 11 to 10
+        0, # 11 to 11
+
+        #Direction = 0
+        0, # 00 to 00
+       -1, # 00 to 01
+       +1, # 00 to 10
+       -2, # 00 to 11
+
+       +1, # 01 to 00
+        0, # 01 to 01
+       -2, # 01 to 10
+       -1, # 01 to 11
+
+       -1, # 10 to 00
+       -2, # 10 to 01
+        0, # 10 to 10
+       +1, # 10 to 11
+
+       -2, # 11 to 00
+       +1, # 11 to 01
+       -1, # 11 to 10
+        0, # 11 to 11
+    ])
+
+
+counter = 0
+direction = 0
+lut_index = 0
+
+def encoder_state_changed_irq_handler(sm):
+    global counter, direction, lut_index
+    lut_index |= sm.get() & 3
+    counter += state_look_up_table[lut_index]
+    if state_look_up_table[lut_index] != 0:
+        direction = 1 if (state_look_up_table[lut_index] > 0) else 0
+    lut_index = ((lut_index << 2) & 0b1100) | (direction << 4)
+ 
+ 
+@rp2.asm_pio()
+def pio_quadrature(in_init=rp2.PIO.IN_LOW):
+    wrap_target()
+    label("again")
+    in_(pins, 2)
+    mov(x, isr)
+    jmp(x_not_y, "push_data")
+    mov(isr, null)
+    jmp("again")
+    label("push_data")    
+    push()
+    irq(block, rel(0))
+    mov(y, x)
+    wrap()
+    
+    
+ 
+sm = StateMachine(0, pio_quad, freq=160000, in_base=Pin(2))
+sm.irq(encoder_state_changed_irq_handler)
+sm.exec("set(y, 99)")  # add a last value for y that would be always different then the input
+sm.active(1)
+
+while True:    
+    utime.sleep(2)
+    print(counter)

From 5366ead756cc04a322be6e0196b3e444052156e8 Mon Sep 17 00:00:00 2001
From: Sandor Attila Gerendi <sanyi@users.noreply.github.com>
Date: Tue, 28 Dec 2021 12:01:48 +0200
Subject: [PATCH 2/3] Fixes missing import and botched refactoring

reported by robert-hh
---
 examples/rp2/pio_quadrature_encoder.py | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/examples/rp2/pio_quadrature_encoder.py b/examples/rp2/pio_quadrature_encoder.py
index 2fa38e8a12..7945b3410b 100644
--- a/examples/rp2/pio_quadrature_encoder.py
+++ b/examples/rp2/pio_quadrature_encoder.py
@@ -9,6 +9,7 @@ https://electronics.stackexchange.com/questions/360637/quadrature-encoder-most-e
 """
 
 from machine import Pin
+import rp2
 from rp2 import PIO, StateMachine
 import utime
 import array
@@ -89,7 +90,7 @@ def pio_quadrature(in_init=rp2.PIO.IN_LOW):
     
     
  
-sm = StateMachine(0, pio_quad, freq=160000, in_base=Pin(2))
+sm = StateMachine(0, pio_quadrature, freq=160000, in_base=Pin(2))
 sm.irq(encoder_state_changed_irq_handler)
 sm.exec("set(y, 99)")  # add a last value for y that would be always different then the input
 sm.active(1)

From c79be30ca661194d50fb1dc5a4af70aef50d29f4 Mon Sep 17 00:00:00 2001
From: Sandor Attila Gerendi <sanyi@users.noreply.github.com>
Date: Thu, 30 Dec 2021 17:50:12 +0200
Subject: [PATCH 3/3] Cater for the case where another state change occurs
 while the ISR is running.

Thank you peterhinch
---
 examples/rp2/pio_quadrature_encoder.py | 11 ++++++-----
 1 file changed, 6 insertions(+), 5 deletions(-)

diff --git a/examples/rp2/pio_quadrature_encoder.py b/examples/rp2/pio_quadrature_encoder.py
index 7945b3410b..cc6cf2ec51 100644
--- a/examples/rp2/pio_quadrature_encoder.py
+++ b/examples/rp2/pio_quadrature_encoder.py
@@ -66,11 +66,12 @@ lut_index = 0
 
 def encoder_state_changed_irq_handler(sm):
     global counter, direction, lut_index
-    lut_index |= sm.get() & 3
-    counter += state_look_up_table[lut_index]
-    if state_look_up_table[lut_index] != 0:
-        direction = 1 if (state_look_up_table[lut_index] > 0) else 0
-    lut_index = ((lut_index << 2) & 0b1100) | (direction << 4)
+    while sm.rx_fifo():
+        lut_index |= sm.get() & 3
+        counter += state_look_up_table[lut_index]
+        if state_look_up_table[lut_index] != 0:
+            direction = 1 if (state_look_up_table[lut_index] > 0) else 0
+        lut_index = ((lut_index << 2) & 0b1100) | (direction << 4)
  
  
 @rp2.asm_pio()