.\" Copyright (c) 1997
.\"      Michael Smith
.\"
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.Dd January 2, 1998
.Dt PPI 4
.Os
.Sh NAME
.Nm ppi
.Nd "user-space interface to ppbus parallel 'geek' port"
.Sh SYNOPSIS
.Cd "device ppi"
.Pp
Minor numbering: unit numbers correspond directly to ppbus numbers.
.Pp
.In dev/ppbus/ppi.h
.In dev/ppbus/ppbconf.h
.Sh DESCRIPTION
The
.Nm
driver provides a convenient means for user applications to manipulate the
state of the parallel port, enabling easy low-speed I/O operations without
the security problems inherent with the use of the
.Pa /dev/io
interface.
.Sh PROGRAMMING INTERFACE
All I/O on the
.Nm
interface is performed using
.Fn ioctl
calls.
Each command takes a single
.Ft uint8_t
argument, transferring one byte of data.
The following commands are available:
.Bl -tag -width indent
.It Dv PPIGDATA , PPISDATA
Get and set the contents of the data register.
.It Dv PPIGSTATUS , PPISSTATUS
Get and set the contents of the status register.
.It Dv PPIGCTRL , PPISCTRL
Get and set the contents of the control register.
The following defines correspond to bits in this register.
Setting a bit in the control register drives the corresponding output low.
.Bl -tag -width indent -compact
.It Dv STROBE
.It Dv AUTOFEED
.It Dv nINIT
.It Dv SELECTIN
.It Dv PCD
.El
.It Dv PPIGEPP , PPISEPP
Get and set the contents of the EPP control register.
.It Dv PPIGECR , PPISECR
Get and set the contents of the ECP control register.
.It Dv PPIGFIFO , PPISFIFO
Read and write the ECP FIFO (8-bit operations only).
.El
.Sh EXAMPLES
To present the value 0x5a to the data port, drive STROBE low and then high
again, the following code fragment can be used:
.Bd -literal -compact

	int		fd;
	uint8_t		val;

	val = 0x5a;
	ioctl(fd, PPISDATA, &val);
	ioctl(fd, PPIGCTRL, &val);
	val |= STROBE;
	ioctl(fd, PPISCTRL, &val);
	val &= ~STROBE;
	ioctl(fd, PPISCTRL, &val);

.Ed
.Sh BUGS
The inverse sense of signals is confusing.
.Pp
The
.Fn ioctl
interface is slow, and there is no way (yet) to chain multiple operations together.
.Pp
The headers required for user applications are not installed as part of the
standard system.