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Re: Etymology of 'softc'

On Fri, 29 Jul 2011 18:44:06 -0400
Greg Troxel <> wrote:

>   Anyone knows what is the etimology for softc?
>   What does it mean? Where does it come from? When was it first used?
> In PDP-11 context, CSR means "control and status register".  Often there
> was an address (for a 16-bit word) that was for control and status, and
> another one for data.  For example, the DL-11 (and DLV-11 on QBUS) had a
> receive CSR at 177560, and receive data at 177562*.  I have always
> interpreted softc as "software c(control/status)", being data that the
> driver keeps state on, but which is not stored in the hardware.
> I remember softc being present in 2.8BSD, probably mid 80s, and I would
> guess that it was introduced very early in the BSD days, in the original
> networking code.  serial devices don't need so much state, and the
> information that is in the softc in a network device (queues, etc.)  are
> in the tty structure, roughly analogous to the common ethernet data
> structure.
> * (seems accurate from my memory)

This seems to confirm some of your theory:

This code mentions it as 'soft carrier' in a comment, but I have
found no other references to it:

NetBSD - Simplicity is prerequisite for reliability

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