On 2025-08-04 17:08, Paul Koning wrote:
On Aug 4, 2025, at 10:45 AM, Johnny Billquist <bqt%softjar.se@localhost>wrote: I'll just top-post to be lazy. First of all, as you know, MOP is the "native" way to netboot DEC machines from back in the day. And MOP sortof fills the place of both DHCP and TFTP in one. But it's more targeted for the explicit need of netbootingand remote management. But in a sense, for VAXen, it would be great if we had the possibility of getting all the netbooting though MOP and not need DHCP and TFTP. Not sure if that is possible, though. I guess MOP didn't really become that relevant with VAXen until the uVAX II (that one was able to netboot, right?). There were net-bootable PDP-11 systems as well, which also used MOP, and which were earlier. But pretty much all the handling of MOP on those machines were actually located in the ethernet controller itself. The CPU was pretty much just in a tight loop until the controller brought it out of there. But that was primarily for the PDP-11. On VAXen, MOP was implemented in the boot monitors. Not sure you can even use the MOP in the controller itself if you're on a VAX. But so, for simh, the controllers do implement at least parts of the MOP on that side. For VAXen, with something like the 3900, the boot roms from the actual machine are included, if I remember right, and so MOP booting will definitely work there no matter what else simh might do. JohnnyI don't think that's entirely accurate. From the Ethernet device pointof view, MOP packets are just packets, it doesn't know or care what theymean. (Well, with the exception of the "trigger" packet, for that to besupported requires the device to check for it and yank on the reset lineif one is seen. Not clear if VAXen ever did this, but I think PDP11s can do this at least with a DEUNA.)
It does depend on the controller, but what I wrote is not disagreeing with what you say. But the fact is that MOP in the DEUNA, DELUA and DELQA are implemented (in parts) in the controller itself. The host machine (PDP-11) does not talk MOP at all during boot. It just goes into a state where it waits for the controller to break it out of its wait.
If you want to boot from the boot monitor, you do need boot roms for that to be possible, but if you remote trigger a boot (something MOP can do), then your machine don't even need any boot roms for it to happen.
It is documented in some parts in the RSX DECnet manuals, and also the manuals for the different controllers. And as far as I know, the only MOP bootable PDP-11 system from DEC is/was RSX-11S.
Reading through the DEUNA right now. It actually forces ACLO on the Unibus to stop the processor, and control it's execution during the MOP BOOT command. Which can be triggered over the network (even to a halted processor), at power on, and also via local boot roms, and thus the local boot monitor, or whatever you want to call whatever you have on the M9312.
The DELQA (just did a brief check) can actually load into memory from the controller a more extensive PDP-11 boot program, which can then be executed by the host, but this is for PDP-11 only. For VAX, you need code in the VAX boot roms.
As far as I remember, the DELUA works pretty much like the DEUNA.So for Unibus machines, the CPU is definitely not involved at all. Qbus - it sortof depends, you could say...
But all of this is in the microcode of the respective controller. So it is in the controller itself, and it's obviously more than just about transmitting and receiving ethernet packets. Those controllers have a lot of additional stuff in there. They also understand a bunch of other MOP packets and handle them internally, and also generate MOP packets on a regular basis on their own, without the host being involved, or aware...
MicroVAX would certainly be an example of a system able to use MOP. Itwas, I believe, the engine in the LPS40 laser printer, which was netbooted as far as I can remember (into VAXeln, not VMS or NetBSD).
For sure. But also DECservers, like the 550, which is PDP-11 based, with a Qbus. And which booted into some DECserver system. But also, really, RSX-11S.
Johnny
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Johnny Billquist || "I'm on a bus
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