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Add good description of init and lock devices from sio to uart.

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Warner Losh 2018-08-14 13:52:10 +00:00
parent bd9325a169
commit 29989b4558
1 changed files with 46 additions and 0 deletions
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46
share/man/man4/uart.4
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@ -225,6 +225,52 @@ Generally speaking, a connection to a DB-9 style connector is an RS-232
level signal at up to 12 volts.
A connection to header pins or an edge-connector on an embedded board
is typically a TTL signal at 3.3 or 5 volts.
.Sh Special Devices
The
.Nm
driver also supports an initial-state and a lock-state control
device for each of the callin and the callout "data" devices.
The termios settings of a data device are copied
from those of the corresponding initial-state device
on first opens and are not inherited from previous opens.
Use
.Xr stty 1
in the normal way on the initial-state devices to program
initial termios states suitable for your setup.
.Pp
The lock termios state acts as flags to disable changing
the termios state.
E.g., to lock a flag variable such as CRTSCTS, use
.Em stty crtscts
on the lock-state device.
Speeds and special characters
may be locked by setting the corresponding value in the lock-state
device to any nonzero value.
E.g., to lock a speed to 115200, use
.Dq Li stty 115200
on the initial-state device and
.Dq Li stty 1
on the lock-state device.
.Pp
Correct programs talking to correctly wired external devices
work with almost arbitrary initial states and almost no locking,
but other setups may benefit from changing some of the default
initial state and locking the state.
In particular, the initial states for non (POSIX) standard flags
should be set to suit the devices attached and may need to be
locked to prevent buggy programs from changing them.
E.g., CRTSCTS should be locked on for devices that support
RTS/CTS handshaking at all times and off for devices that do not
support it at all.
CLOCAL should be locked on for devices that do not support carrier.
HUPCL may be locked off if you do not
want to hang up for some reason.
In general, very bad things happen
if something is locked to the wrong state, and things should not
be locked for devices that support more than one setting.
The CLOCAL flag on callin ports should be locked off for logins
to avoid certain security holes, but this needs to be done by
getty if the callin port is used for anything else.
.Sh FILES
.Bl -tag -width "/dev/ttyu?.init" -compact
.It Pa /dev/ttyu?