Experimental Physics and
Industrial Control System

Michael Abbott <[email protected]> · Wed, 2 Jun 2010 10:22:20 +0100 (BST)

While working on rsrv/camessage.c, I've noticed a curious discrepancy 
between the header preparation code in cas_copy_in_header() and the 
protocol document at
	http://epics.cosylab.com/cosyjava/JCA-Common/Documentation/CAproto.html

In section 3.1 we are told that the maximum short form payload length is 
0x4000 bytes, but in the code the maximum generated payload length appears 
to be 0xFFFE bytes.

Presumably, as this code has been in use for quite a long time, the 
protocol document is in error, or perhaps is a little unclear?  As I read 
it, the document is saying that the extended header must be used for 
payloads longer than 0x3ff0.

Also, presumably, the statement that extended headers cannot be used for 
short payloads is unecessarily restrictive?

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System