On 2025-08-05 02:56, Paul Koning wrote:
On Aug 4, 2025, at 5:42 PM, Johnny Billquist <bqt%softjar.se@localhost> wrote: 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 aVAX. But so, for simh, the controllers do implement at least parts of theMOP on that side. For VAXen, with something like the 3900, the boot romsfrom 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 DELQAare 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.That's interesting. I always thought of trigger as something that justyanks ACLO (as you mentioned) and lets the boot ROM do the loading, withthe Ethernet NIC as just the device that the ROM code talks to. Having the job in the controller obviously works too, but I wonder why it would be done that way.
I would guess the primary reason is/was that the M9312 boot roms are just way to small to contain anything close to a MOP implementation. Each boot rom is 64 bytes. If I remember right, the XE: requires two boot roms, even when pretty much everything is in the controller. But if you manage to implement MOP in even 256 bytes (the size of all four boot roms combined), I would be very impressed.
But think about it. Even detecting and processing the trigger requires something to receive and process a MOP message. And this could be for a CPU halted. How would you do that unless the controller itself understands MOP?
The DELQA, as I mentioned, have a larger chunk of code in the controller that can be transferred over and executed. That's about 4K of code, if I remember the manual correctly. But that transfer can only happen at the request of the CPU, so if a remote trigger happens, it needs to be processed and action taken without any involvement from the CPU.
The DMC MOP boot, as far as I know, is in boot ROMs, I remember the M-whatever model variant listing for that.
Yeah. And if I remember right, those take three boot roms. And that's a much simpler implementation, and it will not be able to be triggered remotely if the machine isn't running. So only at power on, or when the machine is already running with a functional DECnet stack (well, DDCMP and MOP).
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: bqt%softjar.se@localhost || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol