Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Wed, 26 Oct 2005 15:57:06 -0500

Jeff Hill wrote:

Attached is a rough cut at the EPICS V4 CA protocol specification.

Thanks Jeff.

PS: Andrew, its fine to put this up on the web / wiki if you would like.

Great, I've now done that. Could we make the wiki version the canonical

one? It's a bit of a pain to convert as I've just discovered that the

converter I use discards the content of any table cell that consists of

just a numeric zero, so I had to add all your zero values back by hand

(I hope I didn't miss any!).

A couple of comments on the simpler stuff early on:

There is no single IEEE standard for a 128 bit float; there are many

possible 128 bit formats that can all legitimately claim to fall into

the IEEE754 category called Double Extended Precision. Your FLOAT128

doesn't specify which of these you'll be passing over the wire, although

I realise that you're probably wanting to use what is commonly referred

to as quadruple precision. RFC 1832 http://rfc.net/rfc1832.html#s3.8

defines this format for XDR, and I believe both 64-bit SPARC and PowerPC

CPUs support it natively, and possibly other recent chips too.

The bit numbering in the UINTN tables is wrong. The general case should

be that in Octet n (counting from 0), bits 6-0 contain bits n*7+6 thru

n*7 of the unsigned value, i.e. successive octets will contain bits 6-0,

13-7, 20-14 etc.

Note that I have not made any changes in the Wiki version other than

reformatting your distributed text.

- Andrew
--
English probably arose from Normans trying to pick up Saxon girls.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System