FS: Improve reliability on speeds with poor optical tracking

Depending on the filament surface and moving speed, the PAT9125 sensor
can stop being able to track movement.

In such cases, instead of triggering false errors and/or relying on
previous states, read and use the exposure data off the sensor and
increase error counts only for poorly exposed images instead, which
is a good indicator of a far-away (or missing!) tracking surface.

Firmware/fsensor.cpp

@@ -488,10 +488,25 @@ ISR(FSENSOR_INT_PIN_VECT)
 
         if (pat9125_y == 0)
         {
-            // no movement detected: increase error count only when extruding, since fast retracts
-            // cannot always be seen. We also need to ensure that no runout is generated while
-            // retracting as it's not currently handled everywhere
-            if (st_dir) ++fsensor_err_cnt;
+            if (st_dir)
+            {
+                // no movement detected: we might be within a blind sensor range,
+                // update the frame and shutter parameters we didn't earlier
+                if (!fsensor_oq_meassure)
+                    pat9125_update_bs();
+
+                // increment the error count only if underexposed: filament likely missing
+                if ((pat9125_b < 80) && (pat9125_s > 10))
+                {
+                    // check for a dark frame (<30% avg brightness) with long exposure
+                    ++fsensor_err_cnt;
+                }
+                else
+                {
+                    // good frame, filament likely present
+                    if(fsensor_err_cnt) --fsensor_err_cnt;
+                }
+            }
         }
         else if (pat9125_dir != st_dir)
         {

Firmware/pat9125.c

@@ -219,19 +219,13 @@ uint8_t pat9125_update_y(void)
 	return 0;
 }
 
-uint8_t pat9125_update_y2(void)
+uint8_t pat9125_update_bs(void)
 {
 	if ((pat9125_PID1 == 0x31) && (pat9125_PID2 == 0x91))
 	{
-		uint8_t ucMotion = pat9125_rd_reg(PAT9125_MOTION);
-		if (pat9125_PID1 == 0xff) return 0; //NOACK error
-		if (ucMotion & 0x80)
-		{
-			int8_t dy = pat9125_rd_reg(PAT9125_DELTA_YL);
-			if (pat9125_PID1 == 0xff) return 0; //NOACK error
-			pat9125_y -= dy; //negative number, because direction switching does not work
-		}
-		return 1;
+		pat9125_b = pat9125_rd_reg(PAT9125_FRAME);
+		pat9125_s = pat9125_rd_reg(PAT9125_SHUTTER);
+		if (pat9125_PID1 == 0xff) return 0;
 	}
 	return 0;
 }

Firmware/pat9125.h

@@ -19,9 +19,9 @@ extern uint8_t pat9125_b;
 extern uint8_t pat9125_s;
 
 extern uint8_t pat9125_init(void);
-extern uint8_t pat9125_update(void);
-extern uint8_t pat9125_update_y(void);
-extern uint8_t pat9125_update_y2(void);
+extern uint8_t pat9125_update(void);    // update all sensor data
+extern uint8_t pat9125_update_y(void);  // update _y only
+extern uint8_t pat9125_update_bs(void); // update _b/_s only
 
 
 #if defined(__cplusplus)