ad.4

早期freebsd实现

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.\"     @(#)ad.4	8.1 (Berkeley) 6/5/93
.\"
.Dd June 5, 1993
.Dt AD 4 vax
.Os BSD 4.2
.Sh NAME
.Nm ad
.Nd Data Translation A/D converter
.Sh SYNOPSIS
.Cd "device ad0 at uba0 csr 0170400 vector adintr"
.Sh DESCRIPTION
The
.Nm \&ad
driver
provides an interface to the Data Translation A/D converter.
This is
.Em not
a real-time driver, but merely allows
the user process to sample the board's channels one at a time.
Each minor device selects a different
.Tn A/D
board.
.Pp
The driver communicates to a user process by means of
.Xr ioctl 2 Ns s.
The
.Dv AD_CHAN
.Xr ioctl
selects which channel of the board to read.
For example,
.Bd -literal -offset indent
chan = 5;
ioctl(fd, AD_CHAN, &chan);
.Ed
.Pp
selects channel 5.
The
.Dv AD_READ
.Xr ioctl 2
actually reads the data and returns it to the user
process.
An example is
.Bd -literal -offset indent
ioctl(fd, AD_READ, &data);
.Ed
.Sh FILES
.Bl -tag -width /dev/adx -compact
.It Pa /dev/ad
.El
.Sh DIAGNOSTICS
None.
.Sh HISTORY
The
.Nm
driver appeared in
.Bx 4.1 .