On 2017-02-06 00:40, Mark Pizzolato wrote:
On Sunday, February 5, 2017 at 2:48 PM, Timothe Litt wrote:
On 05-Feb-17 16:15, Johnny Billquist wrote:
On 2017-02-05 21:31, Mark Pizzolato wrote:
A concept related to this discussion is simh's auto sizing of disks.
In the PDP11 and
VAX simulators the RQ and RP disks use the sim_disk library to
perform I/O to disk Images and/or physical disk devices.
So, I'd like to expand the set of file system types that the auto
sizing logic can perform to include RSTS disks and whatever might be
commonly used with RSX and RT11. I can certainly give all the
information you need for ODS-1, which is what RSX use. The structures
are pretty similar to ODS-2, so if you already have that, it should
be very simple to add the ODS-1 stuff.
Unfortunately, this will only cover RSX systems. For RT-11 (as well as
RSTS/E and others), you'll have to get someone else to help. I suspect
Paul should know RSTS/E, if he just have the time.
Anyway, the gist in ODS-1 is that the size of the device is contained
in a file called BITMAP.SYS (FID 2,2,0). In there, there is a 32-bit
value saying what the size of the disk is in logical blocks.
For ODS-2, you want the SCB, which is contained in BITMAP.SYS. It gets tricky,
especially where geometry is involved and where the emulated disk image is a
physical copy of media that doesn't match the SCB.
I have code that navigates ODS-2 and attempts to identify the correct disk
based on the recorded geometry. It's part of an ODS-2 reader/writer. I need
to get back to that project and finish some higher-level stuff; when it's
released
you can extract that code for SimH. It's about 5 down on my stack, which I'm
unlikely to reach before April/May.
I've already done the ODS2 case and the Ultrix case, so nothing needed for that.
Now that Johnny pointed me to the ODS1 spec, I'm adding the appropriate file
system structure definitions right now. I have enough to solve this case.
Mark, I found a slightly revised ODS-1 spec that gives an alternative
interpretation of the SCB block in BITMAP.SYS on ODS-1 for large disks.
DEC did a revision.
Putting that up as well, as http://mim.update.uu.se/ods1-1
And the size limit mentioned is not correct. I seem to remember there is
also a file level 403, and the limit of ODS-1 with 3+1 retrieval
pointers are in fact 8G. I don't think that file level changes anything
on how you find the disk size, though.
Johnny
--
Johnny Billquist || "I'm on a bus
|| on a psychedelic trip
email: [email protected] || Reading murder books
pdp is alive! || tryin' to stay hip" - B. Idol
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