[Simh] Byte capacity

[Rob Jarratt]

To be honest I am a little confused by your response. In my VAX 780
emulation I am using RQ as an RA92. This has a real-world size of 1.5GB and
capac=1505766912 while dwidth=16. In this case capac is giving me the value
I would expect. In the PDP11 emulation I am using RP as an RP04, which I
believe is about 85MB. In this case I get capac=43980288 and dwidth=16. So
capac in this case would appear to be half the size in bytes, I can multiply
it by 2 because of the 16-bit word length to get the right size in bytes,
but if I do so then I would calculate a size for the RA92 of 3GB, because it
too has a dwidth of 16, so I would get double the actual size.

What am I missing here?

Thanks

Rob

> -----Original Message-----
> From: simh-bounces at trailing-edge.com [mailto:simh-bounces at trailing-
> edge.com] On Behalf Of Bob Supnik
> Sent: 30 May 2010 19:46
> To: simh at trailing-edge.com
> Subject: [Simh] Byte capacity
> 
> The same way SCP does it:
> 
> (dptr->dwidth + CHAR_BIT - 1) / CHAR_BIT
> 
> You can just use 7 and 8 for constants, if you prefer.
> 
> /Bob
> 
> On 5/30/2010 12:00 PM, simh-request at trailing-edge.com wrote:
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> >     1.  Simulated disk size (Rob Jarratt)
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> > ---------------------------------------------------------------------
> -
> >
> > Message: 1
> > Date: Sat, 29 May 2010 23:41:00 +0100
> > From: "Rob Jarratt"<robert.jarratt at ntlworld.com>
> > Subject: [Simh] Simulated disk size
> > To:<simh at trailing-edge.com>
> > Message-ID:<01bf01caff80$0615cff0$12416fd0$@jarratt at ntlworld.com>
> > Content-Type: text/plain; charset="us-ascii"
> >
> > I have recently discovered that my difference disk code does not work
> well
> > with all simulated disks. I had tested it with the RQ disks in the
> VAX 780
> > emulation. Recently I have had occasion to try the PDP 11 simulation
> and I
> > have discovered that my code does not work with RP disks. This is
> because I
> > rely on the capac field in the sim_unit structure. From what I can
> tell this
> > field is the number of bytes for an RQ disk, but the number of 16-bit
> words
> > for an RP. Is there a consistent way for me to discover the size of a
> > simulated disk in bytes?
> >
> > Regards
> >
> > Rob
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