Merge branch 'btp-frame-length' into 'master'

Maximum encrypted frame length should be 1,024 bytes

See merge request !5

protocols/BTP.md

@@ -254,7 +254,7 @@ The random nonce ensures that even if a stream number is accidentally reused, th
 
 ### 3.3 Frames
 
-The remainder of the stream consists of one or more frames. Each frame has a fixed-length **frame header** and a variable-length **frame body** that may contain data and/or padding. The total length of the data and padding must be less than 2<sup>15</sup> bytes.
+The remainder of the stream consists of one or more frames. Each frame has a fixed-length **frame header** and a variable-length **frame body** that may contain data and/or padding. The total length of the data and padding must be no more than 988 bytes, giving a maximum length of 1,024 bytes for an encrypted frame, including the header.
 
 The frames in each stream are numbered from zero. A stream must not contain more than 2<sup>63</sup> frames.
 
@@ -268,7 +268,7 @@ The plaintext frame header is four bytes long, with the following format (where
 
 - Bits 16 - 31: int\_16(len(padding))
 
-The final frame flag overlaps with the most significant bit of the data length, which is unused because the data must be less than 2<sup>15</sup> bytes long.
+The final frame flag overlaps with the most significant bit of the data length, which is unused because the data must be no more than 988 bytes long.
 
 The final frame flag allows the recipient to detect the end of the stream without reading to EOF, which is not possible for all transports on all platforms.