UNIBUS M9312 ROMS

[Paul Koning]

> On Jun 9, 2016, at 12:56 AM, Don North <ak6dn at mindspring.com> wrote:
> 
> On 6/8/2016 5:56 PM, Paul Koning wrote:
>>> On Jun 8, 2016, at 6:46 PM, Jay West <jwest at classiccmp.org> wrote:
>>> 
>>> I wrote...
>>> On Thu, Jun 9, 2016 at 6:34 AM, Jay West <jwest at classiccmp.org> wrote:
>>>> 23-E39A9 is still lost to time, afaik. TMSCP - TU81
>>> To which mike replied...
>>> ----
>>> Could that not be reverse-engineered from the boot code in e.g. Emulex
>>> UC17 ROMs? They could do TMSCP...
>>> 
>>> BTW what PROM blower would folks recommend for creating/imaging M9312 ROMs?
>>> ----
>>> Possibly, but some (me) are sticklers for original code. Plus, I am not sure, but I think someone said this rom did something really bizarre to fit in the available rom space - self modifying code or something...
>> MSCP isn't all that hard.  The RSTS secondary loader fits in one block, and it contains not just code to speak MSCP but also enough room for a map of pointers to where the code to load lives (as opposed to the primary boot which just has to load one block from address zero).
>> 
>> 	paul
> 
> In an M9312 boot PROM there are 49. words of bootstrap space that are available for code and data. Getting an MSCP boot to fit in that space required playing some tricks like treating some specially crafted instructions as data values (and vice versa).

Oh... I didn't realize it was that small.  Yes, that does make it harder.

	paul