On Sun, 1 May 2005, Dan Lanciani wrote:

> |Same as the VAX-11/750. In fact, NetBSD still ships with a patch file for
> |that machine, and starts the boot by patching the microcode for a few
> |bugs.
>
> I remember when we received the (mandatory) upgrade to add the writable
> microcode to our 750. (Did it later become standard?)


Yes, I think so. There is some writeable control store, but not much. It
actually shadows the normal ROM microcode memory. When you write something
to the microcode RAM in an 11/750, RAM is enabled for just that address,
and it replaces the ROM contents.
(If I remember correctly, it was a while since I looked at this.)

> There was a lot
> of confusion about how exactly the microcode was to be loaded. They
> gave us a TU58 which in theory was supposed to get read by something at
> powerup, but I'm pretty sure it wasn't. (I always thought there was
> a missing boot ROM update to go with the writable microcode.) VMS had
> some way of loading it as did later Ultrix (pcs750.bin loaded by VMB?),
> but we were running 4.2BSD.


4.3 BSD and newer actually have the loading of the microcode in /vmunix
(or whatever the kernel is called).
It's about the first thing the kernel will do after it realizes that it is
running on an 11/750. It loads /pcs750.bin and puts it in microcode RAM.
(I don't know about 4.2BSD, since I haven't played with it)

Johnny

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