19 Nov
2021
19 Nov
'21
1:50 a.m.
Correction...
Character mode sync in SIMH seems utterly trivial; just treat it as an async stream except
that the device would supply sync bytes when the software isn't feeding it data for a
while. Perhaps just a couple, just enough to act as a boundary; no need to flood the
connection with data.
HDLC mode is different; HDLC is inescapably a packet mode service since the flags are
packet delimiters. A small complication is that it can carry any bit count, not just
whole bytes. So the network encoding of a simulated HDLC device needs to handle that. A
UDP encoding could just be a packet containing the data bytes, with one byte appended to
specify how many bits in the last data byte are meaningful. (So a typical whole-byte
packet might be "abcdefgh\010".) A TCP encoding could be similar with a packet
length at the start. If it's desirable not to buffer whole frames, the stream could
be broken into fragments with the last one (where the flag appears) marked as last. That
would be necessary if arbitrary length frames are wanted, though a sensible protocol
doesn't use frames longer than a thousand bytes or so since the 16-bit CRC isn't
strong enough for really long frames.
paul
On Nov 18, 2021, at 7:12 PM, Paul Koning
<paulkoning at comcast.net> wrote:
It seems like a very simple matter to simulate it as a basic character device, separate
from the KMC pairing. The only real question is how you represent a sync data stream in a
simullated device. Is it just the byte stream over a TCP connection? That would be easy
for synchronous character mode. If you also want to simulate HDLC sync devices,
that's a different matter entirely; there isn't an obvious way to do that.
In other words, if someone wants this, just design how it communicates and do the code,
it doesn't sound hard.
paul
> On Nov 18, 2021, at 6:35 PM, R. Voorhorst <R.Voorhorst at swabhawat.com>
wrote:
>
> No, the Dup is only simulated as Kdp/Dup combo, hence the Ddcmp characteristics of
the pair.
>
>
> Reindert
>
> -----Original Message-----
> From: owner-hecnet at Update.UU.SE [mailto:owner-hecnet at Update.UU.SE] On Behalf Of
Johnny Billquist
> Sent: Friday, 19 November, 2021 00:31
> To: hecnet at Update.UU.SE
> Subject: Re: [HECnet] ANF10 network --> DN200 (RJE, Decnet) --> should be Ddcmp
--Re2
>
> Fair enough.
>
> But DUP11 is a sync character based interface. So that one too requires that you do
DDCMP in software. But I didn't think simh simulated a DUP11?
>
> Johnny