Announcing TCP/IP for RSX-11M-PLUS

Johnny Billquist bqt at
Wed Jan 14 16:08:23 CST 2015

On 2015-01-14 17:55, Pontus Pihlgren wrote:
> On Wed, Jan 14, 2015 at 09:21:32AM -0500, Noel Chiappa wrote:
>>      > From: Johnny Billquist
>>      > But for people who actually wants to read several hundred K of
>>      > MACRO-11... Here is your chance... :-)
>> Ah. Was going to ask what the TCP/IP itself was written in. Well, at least
>> it's an 8-bit machine - think about writing a TCP/IP in PDP-10 MACRO... :-)
>> 	Noel
> Do you mean to say that bytes are 8-bit wide on PDP-11? Why
> would PDP-10 be so much harder?

There are lots of things that becomes complex and/or odd when you are on 
a machine with a word size that is not evenly divisible by 8.
You need to manipulate bitfields inside a word, and depending on how 
things work, you might either span word boundaries, placing half of an 
octet in one word and the other half in the second, or else have four 
extra bits sitting around that you should ignore in every word.
All arithmetic are done on 16- or 32-bit quantities, which you must take 
into consideration. The IP checksum is an odd beast that do ones 
complement addition. So spillover from the 16-bit additions are added 
back at the bottom.

Everything is of course doable, but there will be a whole lot of bit 
fiddling and juggling doing TCP/IP on a PDP-10.


Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol

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