Add sideset assembly support.

You must also set `sideset_enable` when creating the rp2pio.StateMachine
object.

Fixes adafruit#16 and fixes adafruit#21.

Author: tannewt

adafruit_pioasm.py

@@ -55,6 +55,7 @@ def assemble(text_program):
             pass
         elif line.startswith(".side_set"):
             sideset_count = int(line.split()[1])
+            sideset_enable = 1 if "opt" in line else 0
         elif line.endswith(":"):
             label = line[:-1]
             if label in labels:
@@ -64,7 +65,7 @@ def assemble(text_program):
             # Only add as an instruction if the line isn't empty
             instructions.append(line)
 
-    max_delay = 2 ** (5 - sideset_count) - 1
+    max_delay = 2 ** (5 - sideset_count - sideset_enable) - 1
     assembled = []
     for instruction in instructions:
         # print(instruction)
@@ -76,10 +77,13 @@ def assemble(text_program):
                 raise RuntimeError("Delay too long:", delay)
             instruction.pop()
         if len(instruction) > 1 and instruction[-2] == "side":
+            if sideset_count == 0:
+                raise RuntimeError("No side_set count set")
             sideset_value = int(instruction[-1])
             if sideset_value > 2 ** sideset_count:
                 raise RuntimeError("Sideset value too large")
-            delay |= sideset_value << (5 - sideset_count)
+            delay |= sideset_value << (5 - sideset_count - sideset_enable)
+            delay |= sideset_enable << 4
             instruction.pop()
             instruction.pop()
 
@@ -186,6 +190,6 @@ def assemble(text_program):
         else:
             raise RuntimeError("Unknown instruction:" + instruction[0])
         assembled[-1] |= delay << 8
-    # print(hex(assembled[-1]))
+        # print(bin(assembled[-1]))
 
     return array.array("H", assembled)

examples/txuart.py

@@ -0,0 +1,52 @@
+# SPDX-FileCopyrightText: 2021 Jeff Epler, written for Adafruit Industries
+#
+# SPDX-License-Identifier: MIT
+
+import rp2pio
+import adafruit_pioasm
+
+code = adafruit_pioasm.assemble(
+    """
+.program uart_tx
+.side_set 1 opt
+
+; An 8n1 UART transmit program.
+; OUT pin 0 and side-set pin 0 are both mapped to UART TX pin.
+
+  pull side 1 [7] ; Assert stop bit, or stall with line in idle state
+  set x, 7 side 0 [7] ; Preload bit counter, assert start bit for 8 clocks
+bitloop: ; This loop will run 8 times (8n1 UART)
+  out pins, 1 ; Shift 1 bit from OSR to the first OUT pin
+  jmp x-- bitloop [6] ; Each loop iteration is 8 cycles.
+
+"""
+)
+
+class TXUART:
+    def __init__(self, *, tx, baudrate=9600):
+        self.pio = rp2pio.StateMachine(
+            code,
+            first_out_pin=tx,
+            first_sideset_pin=tx,
+            frequency=8 * baudrate,
+            initial_sideset_pin_state=1,
+            initial_sideset_pin_direction=1,
+            initial_out_pin_state=1,
+            initial_out_pin_direction=1,
+            sideset_enable=True
+        )
+
+    @property
+    def timeout(self):
+        return 0
+
+    @property
+    def baudrate(self):
+        return self.pio.frequency // 8
+
+    @baudrate.setter
+    def baudrate(self, frequency):
+        self.pio.frequency = frequency * 8
+
+    def write(self, buf):
+        return self.pio.write(buf)