> On Sep 21, 2015, at 3:49 PM, Jerome H. Fine <jhfined...@compsys.to> wrote:
>
> >Johnny Billquist wrote:
>
>> >On 2015-09-21 17:03, Paul Koning wrote:
>>
>>> And it would certainly be possible to write a driver that can handle both
>>> controllers; it would start by determining which controller it's dealing
>>> with, and then run the one or the other set of algorithms. Since a boot
>>> block is just a small driver, the same is true there, so long as the whole
>>> body of code fits in the available space. I suspect in this case that's
>>> doable; most bootloaders (other than MSCP ones) require only a small
>>> fraction of the available space.
>>
>> You are absolutely right.
>> And I don't know the actual size of the boot blocks. It might very well be
>> that they both fits in the same boot block, which would be nice.
>> I know that the M9312 have separate boot roms for the RX11 and the RX211,
>> but those boot roms are pretty tiny...
>>
>> And I don't know if the RX211 boot rom also deals with RX01 floppies, but I
>> would assume it does.
>
> I don't know how RSX-11 and RSTS/E manage their device
> drivers and allocate the memory for that code. BUT, under
> RT-11, each device driver uses memory which the user program
> can't use. ...
> Finally, while the boot code could certainly support both
> the RX01 and the RX02 drive, there would be no point
> since the code in the device driver supports only one
> drive.
RSTS isn't as frugal with memory as RT11 is. It has a bit of per-unit memory
whether the device is present or not. But the kernel can be built with all
sorts of device drivers for devices that aren't actually present. If so, those
are disabled at boot.
So for RSTS, it certainly makes sense to have a multi-lingual boot block, if
you're dealing with a medium that can be installed into several types of drives
with different controllers.
The RX01/RX02 case doesn't occur for RSTS since those aren't supported as boot
devices. But the analogous scenario does apply to magtape. The RSTS magtape
boot block works with every PDP-11 controller capable of supporting that tape,
so 1600 BPI tapes can boot on TU16, TS80 (gag) and TMSCP controllers. Yes,
that's a fun bit of code.
paul
