.\" Copyright (c) 1998, 1999, Nicolas Souchu
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.\" $FreeBSD$
.\"
.Dd March 5, 1998
.Dt PPC 4
.Os FreeBSD
.Sh NAME
.Nm ppc
.Nd Parallel Port Chipset driver
.Sh SYNOPSIS
.Cd "device ppc0 at isa? port? flags 0xXX irq 7"
.Pp
For one or more PPBUS busses:
.Cd "device ppbus at ppc0"
.Sh DESCRIPTION
The
.Nm
driver provides low level support to various parallel port chipsets for the
.Xr ppbus 4
system.
.Pp
During the probe phase, 
.Nm
detects parallel port chipsets and initializes
private data according to their operating mode: COMPATIBLE,
NIBBLE, PS/2, EPP, ECP and other mixed modes. 
If a mode is provided at startup through the 
.Va flags
variable of the boot 
interface, the operating mode of the chipset is forced according to 
.Va flags
and the hardware supported modes.
.Pp
During the attach phase, 
.Nm
allocates a ppbus structure, initializes it and calls the ppbus 
attach function.
.Ss Supported flags
.Bl -item -offset indent
.It
bits 0-3: chipset forced mode(s)
.Bd -literal
PPB_COMPATIBLE  0x0     /* Centronics compatible mode */
PPB_NIBBLE      0x1     /* reverse 4 bit mode */
PPB_PS2         0x2     /* PS/2 byte mode */
PPB_EPP         0x4     /* EPP mode, 32 bit */
PPB_ECP         0x8     /* ECP mode */
.Ed
.Pp
And any mixed values.
.It
bit 4: EPP protocol (0 EPP 1.9, 1 EPP 1.7)
.It
bit 5: activate IRQ (1 IRQ disabled, 0 IRQ enabled)
.It
bit 6: disable chipset specific detection
.It
bit 7: disable FIFO detection
.El
.Ss Supported chipsets
Some parallel port chipsets are explicitly supported:
detection and initialisation code has been written according to 
their datasheets.
.Bl -bullet -offset indent
.It
SMC FDC37C665GT and FDC37C666GT chipsets
.It
Natsemi PC873xx-family (PC87332 and PC87306)
.It
Winbond W83877xx-family (W83877F and W83877AF)
.It
SMC-like chipsets with mixed modes (see
.Xr ppbus 4 )
.El
.Ss Adding support to a new chipset
You may want to add support for the newest chipset your motherboard was
sold with. 
For the ISA bus, just retrieve the specs of the chipset and write the 
corresponding
.Fn ppc_mychipset_detect ""
function.
Then add an entry to the general purpose
.Fn ppc_detect ""
function. 
.Pp
Your
.Fn ppc_mychipset_detect ""
function should ensure that if the mode field of the
.Va flags
boot variable is not null, then the operating
mode is forced to the given mode and no other mode is available and
ppb->ppb_avm field contains the available modes of the chipset.
.Sh SEE ALSO
.Xr ppbus 4 ,
.Xr ppi 4
.Sh BUGS
The chipset detection process may corrupt your chipset configuration.
You may
disable chipset specific detection by using the above flags.
.Sh HISTORY
The
.Nm
manual page first appeared in
.Fx 3.0 .
.Sh AUTHORS
This manual page was written by
.An Nicolas Souchu .