fix: isolate fan writes from active RGB frames

app/pigway_pi_control.py

@@ -98,6 +98,9 @@ def bus_write(method,*args):
             raise
 
 fan_level=0
+fan_initialized=False
+pending_fan=None
+pending_fan_lock=threading.Lock()
 prev_cpu=None
 page=0; page_since=time.monotonic()
 cpu_hi=mem_hi=0
@@ -180,13 +183,32 @@ def fan_target(t):
     if t<FAN_T[4]: return 4
     return 5
 def update_fan(t):
-    global fan_level
-    want=fan_target(t); old=fan_level
+    global fan_level,fan_initialized,pending_fan
+    want=fan_target(t); old=fan_level if fan_initialized else None
     if want>fan_level: fan_level=want
     elif want<fan_level:
         boundary = FAN_T[max(0,fan_level-1)] - FAN_HYST
         if t < boundary: fan_level-=1
-    if old!=fan_level: mcu(0x08,FAN_REG[fan_level])
+    if not fan_initialized or old!=fan_level:
+        with pending_fan_lock:
+            pending_fan=(old,fan_level,float(t))
+    fan_initialized=True
+
+def apply_pending_fan():
+    global pending_fan
+    with pending_fan_lock:
+        command=pending_fan
+        pending_fan=None
+    if command is None: return
+    old,new,temp=command
+    try:
+        mcu(0x08,FAN_REG[new])
+    except Exception:
+        with pending_fan_lock:
+            if pending_fan is None: pending_fan=command
+        raise
+    log("INFO","FAN_LEVEL",old=FAN_NAME[old] if old is not None else "UNKNOWN",
+        new=FAN_NAME[new],temp_c=f"{temp:.1f}",register=f"0x{FAN_REG[new]:02x}")
 
 def cpu_pct():
     global prev_cpu
@@ -756,6 +778,11 @@ class DisplayController:
                                 rgb_static(NORMAL_COLOR,"normal_flash_on") if on else rgb_off()
                             else: rgb_flash(applied_mode,on)
                         flash_on=on
+                # Fan and RGB share the same MCU.  During an alert flash, send
+                # fan changes only while RGB is already dark so MCU-internal
+                # register handling cannot expose a transient unrelated color.
+                if not applied_flash or flash_on is False:
+                    with bus_lock: apply_pending_fan()
                 if previous_error is not None: log("INFO","RGB_RECOVERED")
                 previous_error=None
             except Exception as e: