[Simh] MOP header specs?

[Paul Koning]

> On Feb 23, 2018, at 5:28 PM, Johnny Billquist <bqt at softjar.se> wrote:
> 
> ...
>> That's why a MOP load normally consists of asking for a program - which is the secondary loader.  It's the secondary (or tertiary) loader that knows how to unpack an image and make additional requests.
> 
> Hum. Well, that might be, but both will be served through MOP, so it don't make much difference if it's the primary or secondary boot. They are served the same way. 

Almost.  A secondary loader response carries the entire secondary loader in a single message, so the bootstrap only needs to handle one message.  Tertiary and OS loads are expected to take multiple messages.

Either way, though, the MOP protocol spec only describes bits on the wire.  How those bits are derived from files on the serving host is a host matter.  Since multiple host types support loading various devices such as routers or terminal servers, it seems likely that they share an on-disk format, but if they do, that's a packaging convenience question, not something the MOP spec addresses.  

You can think of MOP as a simple data transfer protocol; the fact that clients use it to load executable bits into memory is not required.  The same is true for TFTP, and there the name of the protocol makes the point explicit.  MOP doesn't say it quite so clearly but it is just as true there.

	paul