pw_bluetooth: Add frame_type and poll_final definitions for rfcomm

Add ability to extract the different portions of control.

Change-Id: Ie42ee8bfc14cbd0ad745965f391e1c9f3bcde176
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/254473
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Pigweed-Auto-Submit: Austin Foxley <afoxley@google.com>
Reviewed-by: Ben Lawson <benlawson@google.com>
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pw_bluetooth/public/pw_bluetooth/rfcomm_frames.emb

@@ -84,6 +84,23 @@ struct RfcommFrame:
   let uih = control == RfcommFrameType.UNNUMBERED_INFORMATION_WITH_HEADER_CHECK || control == RfcommFrameType.UNNUMBERED_INFORMATION_WITH_HEADER_CHECK_AND_POLL_FINAL
     -- Helper flag to check whether frame is UIH type, regardless of whether credits are in use.
 
+  let flow_control = control == RfcommFrameType.UNNUMBERED_INFORMATION_WITH_HEADER_CHECK_AND_POLL_FINAL
+    -- Helper to check whether RFCOMM credits are allowed in this frame.
+
+  # Overlapping with control to split up frame_type and poll_final
+
+  1                  [+1]  bits:
+
+    0                  [+4]                 UInt                               frame_type_1
+
+    4                  [+1]                 UInt                               poll_final
+
+    5                  [+3]                 UInt                               frame_type_2
+      -- ETSI TS 07.10 section 5.2.1.3
+
+  let frame_type = frame_type_1+frame_type_2*32
+    -- Helper to extract frame type value without poll_final bit
+
   2                  [+1]  bits:
 
     0                  [+1]                 RfcommLengthExtended               length_extended_flag
@@ -110,7 +127,7 @@ struct RfcommFrame:
 
   let credits_offset = $present(length_extended) ? 4 : 3
 
-  if control == RfcommFrameType.UNNUMBERED_INFORMATION_WITH_HEADER_CHECK_AND_POLL_FINAL && channel != 0:
+  if flow_control && channel != 0:
     credits_offset     [+1]                 UInt                               credits
       -- Credits field can appears as first byte of information when Poll/Final
       -- bit is set on UIH frames and channel is not control (0).