Re: serial console device, and installboot vs. /boot.cfg

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

> I think that's essentially what I see. E.g. with serial cable
> connected to the PC's COM port and /boot.confg "consdev=com0,115200",
> the serial console works well as described elsewhere in this thread.

> If I disonnect the serial cable nothing changes.  [...] NetBSD's
> notion of console has not moved to keyboard+vga --

With most serial ports and many cables (those that don't loop back
modem control signals), the host cannot tell whether there is a cable
connected.  With a GND+TXD+RXD-only cable, while in theory the hardware
may be able to detect the presence of a cable by probing electrical
properties such as capacitance and noise pickup, few-to-no serial ports
are capable of it.

The presence of a cable connected to another serial device (a computer,
terminal, modem, etc) is another story.  If any of the
externally-sourced pins are being driven, _something_ must be
connected, even if only a loopback connector.  While nothing says that
any such pins _must_ be connected, at least one data pin must be driven
for two-way communication.

But, again, it's the rare serial port that can detect/report the
difference between "my receive-data pin isn't being driven and hasn't
been for a long time" and "my receive-data pin is driven mark and has
been for a long time" (for values of "a long time" on the order of "a
dozen or more bit times").

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