Implement DMX serial output

pult/backend/main.py

@@ -1,5 +1,8 @@
 import asyncio
 from typing import *
+from queue import Queue
+from threading import Thread, Lock
+import time
 
 from fastapi import FastAPI, WebSocket, WebSocketDisconnect, Request
 from fastapi.staticfiles import StaticFiles
@@ -7,6 +10,7 @@ from fastapi.responses import FileResponse
 
 from pydantic import BaseModel, Field, ValidationError
 
+import serial
 
 app = FastAPI()
 
@@ -156,7 +160,80 @@ async def ws_handler(ws: WebSocket):
 
 app.mount("/", StaticFiles(directory="frontend", html=True))
 
+dmx_data_lock = Lock()
+dmx_data = [0 for _ in range(len(dmx_state))]
+
+async def dmx_watcher():
+    while True:
+        with dmx_data_lock:
+            for (i, slider) in enumerate(dmx_state):
+                dmx_data[i] = slider.value
+        await asyncio.sleep(1/50)
+
+class DmxWriter(Thread):
+    def __init__(self):
+        super().__init__()
+        self.running = True
+
+    def run(self):
+
+        FPS = 50
+        FRAME_TIME = 1 / FPS
+
+
+        with serial.Serial("/dev/ttyUSB0", 500_000) as ser:
+            payload = bytearray(512)
+            
+            def sync():
+                # wait for sync
+                while True:
+                    b = ser.readline()
+                    if b.strip() == b"Sync.":
+                        return
+                    
+            sync()
+
+            print("initial sync.")
+
+            while self.running:
+                
+                loop_start = time.time()
+
+                with dmx_data_lock:
+                    for (i, value) in enumerate(dmx_data):
+                        payload[i] = value
+                
+                ser.write(payload)
+                ser.flush()
+                
+                response = ser.readline()
+                if response.strip() != b"Ack.":
+                    print(f"received bad response: {response!r}")
+                    sync()
+                    continue
+                
+                loop_time = time.time() - loop_start
+                if loop_time < FRAME_TIME:
+                    time.sleep(FRAME_TIME - loop_time)
+                else:
+                    print("loop took too long!")
+                    
+                print(f"loop time: {1000 * loop_time:0.2f}ms busy, {1000 * (time.time() - loop_start):0.2f}ms total")
+    
+    def stop(self):
+        self.running = False
+
+dmx_writer = DmxWriter()
 
 @app.on_event("startup")
 async def on_startup():
     asyncio.create_task(socket_manager.watch_auto_release())
+    asyncio.create_task(dmx_watcher())
+    dmx_writer.start()
+
+
+@app.on_event("shutdown")
+async def on_shutdown():
+    print("shutdown")
+    dmx_writer.stop()
+    dmx_writer.join()