Move pio_uart.py to transports folder

kmk/transports/pio_uart.py

@@ -0,0 +1,90 @@
+'''
+Circuit Python wrapper around PIO implementation of UART
+Original source of these examples: https://github.com/adafruit/Adafruit_CircuitPython_PIOASM/tree/main/examples (MIT)
+'''
+import adafruit_pioasm
+import rp2pio
+
+tx_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.
+'''
+)
+
+rx_code = adafruit_pioasm.assemble(
+    '''
+.program uart_rx_mini
+
+; Minimum viable 8n1 UART receiver. Wait for the start bit, then sample 8 bits
+; with the correct timing.
+; IN pin 0 is mapped to the GPIO used as UART RX.
+; Autopush must be enabled, with a threshold of 8.
+
+    wait 0 pin 0        ; Wait for start bit
+    set x, 7 [10]       ; Preload bit counter, delay until eye of first data bit
+bitloop:                ; Loop 8 times
+    in pins, 1          ; Sample data
+    jmp x-- bitloop [6] ; Each iteration is 8 cycles
+
+'''
+)
+
+
+class PIO_UART:
+    def __init__(self, *, tx, rx, baudrate=9600):
+        if tx:
+            self.tx_pio = rp2pio.StateMachine(
+                tx_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,
+            )
+        if rx:
+            self.rx_pio = rp2pio.StateMachine(
+                rx_code,
+                first_in_pin=rx,
+                frequency=8 * baudrate,
+                auto_push=True,
+                push_threshold=8,
+            )
+
+    @property
+    def timeout(self):
+        return 0
+
+    @property
+    def baudrate(self):
+        return self.tx_pio.frequency // 8
+
+    @baudrate.setter
+    def baudrate(self, frequency):
+        self.tx_pio.frequency = frequency * 8
+        self.rx_pio.frequency = frequency * 8
+
+    def write(self, buf):
+        return self.tx_pio.write(buf)
+
+    @property
+    def in_waiting(self):
+        return self.rx_pio.in_waiting
+
+    def read(self, n):
+        b = bytearray(n)
+        n = self.rx_pio.readinto(b)
+        return b[:n]
+
+    def readinto(self, buf):
+        return self.rx_pio.readinto(buf)