diff --git a/src/gateware/cxp_frame_pipeline.py b/src/gateware/cxp_frame_pipeline.py
index 08fdceb..cbfba38 100644
--- a/src/gateware/cxp_frame_pipeline.py
+++ b/src/gateware/cxp_frame_pipeline.py
@@ -540,11 +540,18 @@ class Pixel_Gearbox(Module):
         ]
 
 class Pixel_Coordinate_Tracker(Module):
-    """track pixel coordinates."""
+    """
+    Track pixel coordinates
+
+    Assume
+    - camera is in area scan mode
+    - 1X-1Y Tap geometry
+    """
     def __init__(self, res_width):
-    # largest x/y pixel size supported by frame header are 24 bits
+        # largest x/y pixel size supported by frame header are 24 bits
         assert res_width <= 3*char_width
 
+        # line scaning frame will have y_size = 0 and won't trigger the end of frame bit
         self.y_size = Signal(3*char_width)
         self.sink = stream.Endpoint(pixel4x_layout)
 
@@ -694,6 +701,14 @@ class ROI(Module):
         
 
 class Pixel_Parser(Module):
+    """
+    Convert the raw frame data into pixel data
+
+    Currently only support:
+    Pixel format: mono8, mono10, mono12, mono14, mono16
+    Tap geometry: 1X-1Y
+    Scaning mode: area scanning
+    """
     def __init__(self, res_width):
         self.l_size = Signal(3*char_width)
         self.x_size = Signal(3*char_width)