Basic support for driving a display with rpi_ws281x

NOTE: weatherscene.py is known to NOT work under Python 3.x due to
an incompatibility with MicroPython's handling of strings and bytes.

This can be easily resolved although I opted to not do this, to preserve
compabilitity with the original code.

To use this on a Raspberry Pi, try:

    sudo apt install -y python-pip python-requests
    sudo pip install rpi_ws281x

Then connect the display's data line to the Raspberry Pi's GPIO 18 (PCM CLK)
(see https://pinout.xyz/)

References:

- https://github.com/noahwilliamsson/lamatrix/issues/1
- https://github.com/rpi-ws281x/rpi-ws281x-python (userspace WS281x driver)
- https://github.com/jgarff/rpi_ws281x (wiring docs)

README.md

@@ -30,7 +30,7 @@
 
 This is a project to drive a 32x8 or 16x16 LED matrix based on the popular WS2812 RGB LEDs using a microcontroller running [MicroPython](https://micropython.org).  There is experimental support for allowing a more powerful host computer (e.g. a Raspberry Pi Zero W) to remotely control a microcontroller without WiFi (e.g. a Teensy 3.x) and the display connected to it over USB serial.  Low FPS video of a standalone Pycom LoPy 1 development board cycling through the scenes:
 
-![LED matrix animated](docs/lamatrix.gif)
+TODO: implement![LED matrix animated](docs/lamatrix.gif)
 
 Static picture with clock scene.  For some reason the colors aren't captured as vidvid as they are in real life.
 
@@ -47,6 +47,7 @@ Features:
 
 Primary development has been made on [Pycom](https://www.pycom.io)'s development boards, including the (obsolete) LoPy 1 and the newer WiPy 3.  There is also an Arduino [sketch](ArduinoSer2FastLED/ArduinoSer2FastLED.ino) for Teensy 3.1/3.2 boards that implements a custom serial protocol that is spoken by the host software ([main.py](main.py) and [arduinoserialhal.py](arduinoserialhal.py)) that allows the LED matrix to be remotely controlled.
 
+**Update 2021**: If you want to use this with a Raspberry Pi instead of an MCU running MicroPython, see the issue [Using Raspberry PI directly to 8 x 32 not working?](https://github.com/noahwilliamsson/lamatrix/issues/1).
 
 ## Building and deploying the MCU
 

main.py

@@ -36,12 +36,18 @@ if hasattr(sys,'implementation') and sys.implementation.name == 'micropython':
 	tmp = None
 	del uname
 else:
-	# Emulate https://docs.pycom.io/firmwareapi/micropython/utime.html
-	time.ticks_ms = lambda: int(time.time() * 1000)
 	import json
 	import os
 	import signal
-	from arduinoserialhal import ArduinoSerialHAL as HAL
+	# Kludge to allow this project to be used with a Raspberry Pi instead of
+	# an MCU: see https://github.com/noahwilliamsson/lamatrix/issues/1
+	try:
+		# If the rpi_ws281x Python module is available, then use that...
+		from raspberrypihal import RaspberryPiHAL as HAL
+	except:
+		# ...else assume that there's an MCU (driving the display) connected
+		# to a serial port
+		from arduinoserialhal import ArduinoSerialHAL as HAL
 
 gc.collect()
 from renderloop import RenderLoop

raspberrypihal.py

@@ -0,0 +1,58 @@
+# HAL for Raspberry Pi with https://github.com/rpi-ws281x/rpi-ws281x-python
+# See https://github.com/jgarff/rpi_ws281x for more details on this library.
+#
+# The below code assumes the LED strip is connected to GPIO 18 (PCM CLK)
+# (see https://pinout.xyz) and that you've installed the rpi_ws281x library.
+#
+# For Python 2.x:
+#
+#   sudo apt install -y python-pip; sudo pip install rpi_ws281x
+#
+# For Python 3.x:
+#
+#   sudo apt install -y python3-pip; sudo pip3 install rpi_ws281x
+#
+#
+from rpi_ws281x import PixelStrip, Color
+
+# LED strip configuration:
+LED_PIN = 18          # GPIO pin connected to the pixels (18 uses PWM!).
+# LED_PIN = 10        # GPIO pin connected to the pixels (10 uses SPI /dev/spidev0.0).
+LED_FREQ_HZ = 800000  # LED signal frequency in hertz (usually 800khz)
+LED_DMA = 10          # DMA channel to use for generating signal (try 10)
+LED_BRIGHTNESS = 255  # Set to 0 for darkest and 255 for brightest
+LED_INVERT = False    # True to invert the signal (when using NPN transistor level shift)
+LED_CHANNEL = 0       # set to '1' for GPIOs 13, 19, 41, 45 or 53
+
+class RaspberryPiHAL:
+	def __init__(self, config):
+		self.num_pixels = config['LedMatrix']['columns'] * config['LedMatrix']['stride']
+		self.strip = PixelStrip(self.num_pixels, LED_PIN, LED_FREQ_HZ, LED_DMA, LED_INVERT, LED_BRIGHTNESS, LED_CHANNEL)
+		self.strip.begin()
+	def init_display(self, num_pixels=64):
+		self.clear_display()
+	def clear_display(self):
+		c = Color(0, 0, 0)
+		for i in range(self.num_pixels):
+			self.strip.setPixelColor(i, c)
+		self.strip.show()
+	def update_display(self, num_modified_pixels):
+		if not num_modified_pixels:
+			return
+		self.strip.show()
+	def put_pixel(self, addr, r, g, b):
+		self.strip.setPixelColor(addr % self.num_pixels, Color(r, g, b))
+	def reset(self):
+		self.clear_display()
+	def process_input(self):
+		#TODO: implement
+		return 0
+	def set_rtc(self, t):
+		#Not relevant
+		pass
+	def set_auto_time(self, enable=True):
+		#Not relevant
+		pass
+	def suspend_host(self, restart_timeout_seconds):
+		#Not relevant
+		pass