NetBSD-5.0.2/share/man/man9/bitmask_snprintf.9

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.\"     $NetBSD: bitmask_snprintf.9,v 1.10 2008/04/30 13:10:58 martin Exp $
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.Dd July 29, 2007
.Dt BITMASK_SNPRINTF 9
.Os
.Sh NAME
.Nm bitmask_snprintf
.Nd bitmask output conversion
.Sh SYNOPSIS
.In sys/systm.h
.Ft char *
.Fn "bitmask_snprintf" "u_quad_t val" "const char *fmt" "char *buf" "size_t buflen"
.Sh DESCRIPTION
The
.Fn bitmask_snprintf
function formats a bitmask into a mnemonic form suitable for printing.
.Pp
This conversion is useful for decoding bit fields in device registers.
It formats the integer
.Fa val
into the buffer
.Fa buf ,
of size
.Fa buflen ,
using a specified radix and an interpretation of
the bits within that integer as though they were flags.
.Pp
The decoding directive string
.Fa fmt
describes how the bitfield is to be interpreted and displayed.
It follows two possible syntaxes, referred to as
.Dq old
and
.Dq new .
The main advantage of the
.Dq new
formatting is that it is capable of handling multi-bit fields.
.Pp
The first character of
.Fa fmt
may be
.Li \e177 ,
indicating that the remainder of the format string follows the
.Dq new
syntax.
The second character
.Pq the first for the old format
is a binary character representation of the
output numeral base in which the bitfield will be printed before it is decoded.
Recognized radix values
.Pq in C escape-character format
are
.Li \e10
.Pq octal ,
.Li \e12
.Pq decimal ,
and
.Li \e20
.Pq hexadecimal .
.Pp
The remaining characters in
.Fa fmt
are interpreted as a list of bit-position\(endescription pairs.
From here the syntaxes diverge.
.Pp
The
.Dq old
format syntax is series of bit-position\(endescription pairs.
Each begins with a binary character value that represents the position
of the bit being described.
A bit position value of one describes the least significant bit.
Whereas a position value of 32
.Pq octal 40, hexadecimal 20, the ASCII space character
describes the most significant bit.
.Pp
The remaining characters in a bit-position\(endescription pair are the
characters to print should the bit being described be set.
Description strings are delimited by the next bit position value character
encountered
.Pq distinguishable by its value being \*[Le] 32 ,
or the end of the decoding directive string itself.
.Pp
For the
.Dq new
format syntax, a bit-position\(endescription begins with a field type
followed by a binary bit-position and possibly a field length.
The least significant bit is bit-position zero, unlike the
.Dq old
syntax where it is one.
.Bl -tag -width "xxxxx"
.It Cm b\eB
Describes a bit position.
The bit-position
.Fa B
indicates the corresponding bit, as in the
.Dq old
format.
.It Cm f\eB\eL
Describes a multi-bit field beginning at bit-position
.Fa B
and having a bit-length of
.Fa L .
The remaining characters are printed as a description of the field
followed by
.Sq \&=
and the value of the field.
The value of the field is printed in the base specified as the second
character of the decoding directive string
.Ar fmt .
.It Cm F\eB\eL
Describes a multi-bit field like
.Sq f ,
but just extracts the value for use with the
.Sq \&=
and
.Sq \&:
formatting directives described below.
.It Cm \&=\eV
The field previously extracted by the last
.Sq f
or
.Sq F
operator is compared to the byte
.Sq Cm V
.Pq for values 0 through 255 .
If they are equal,
.Sq \&=
followed by the string following
.Sq Cm V
is printed.
This and the
.Sq \&:
operator may be repeated to annotate multiple possible values.
.It Cm :\eV
Operates like the
.Sq \&=
operator, but omits the leading
.Sq \&= .
.El
.Pp
Finally, each field is delimited by a NUL
.Pq Sq \e0
character.
By convention, the format string has an additional NUL character at
the end, following that delimiting the last bit-position\(endescription
pair.
.Pp
The buffer
.Fa buf
passed to
.Nm
must be at least
.Dv KPRINTF_BUFSIZE
bytes in length.
See the source code for the definition of this macro.
.Sh RETURN VALUES
The
.Fn bitmask_snprintf
function returns the buffer
.Fa buf .
The returned string is always NULL-terminated.
.Sh EXAMPLES
Two examples of the old formatting style:
.Bd -literal -offset indent
bitmask_snprintf(3, "\e10\e2BITTWO\e1BITONE", buf, buflen)
\(rA "3\*[Lt]BITTWO,BITONE\*[Gt]"

bitmask_snprintf(0xe860,
       "\e20\ex10NOTBOOT\ex0fFPP\ex0eSDVMA\ex0cVIDEO"
       "\ex0bLORES\ex0aFPA\ex09DIAG\ex07CACHE"
       "\ex06IOCACHE\ex05LOOPBACK\ex04DBGCACHE",
        buf, buflen)
\(rA "e860\*[Lt]NOTBOOT,FPP,SDVMA,VIDEO,CACHE,IOCACHE\*[Gt]"
.Ed
.Pp
An example of the new formatting style:
.Bd -literal -offset indent
bitmask_snprintf(0x800f0701,
       "\e177\e020b\e0LSB\e0b\e1_BITONE\e0f\e4\e4NIBBLE2\e0"
       "f\ex10\e4BURST\e0=\e4FOUR\e0=\exfSIXTEEN\e0"
       "b\ex1fMSB\e0\e0",
        buf, buflen)
\(rA "800f0701\*[Lt]LSB,NIBBLE2=0,BURST=f=SIXTEEN,MSB\*[Gt]"
.Ed
.Sh ERRORS
If the buffer
.Fa buf
is too small to hold the formatted output,
.Fn bitmask_snprintf
will still return the buffer, containing a truncated string.
.Sh SEE ALSO
.Xr printf 9
.Sh CODE REFERENCES
.Pa sys/kern/subr_prf_bitmask.c
.Sh HISTORY
The
.Fn bitmask_snprintf
function was originally implemented as a non-standard
.Li %b
format string for the kernel
.Fn printf
function in
.Nx 1.5
and earlier releases.
.Sh AUTHORS
The
.Dq new
format was the invention of
.An Chris Torek .