NAME

__BIT, __BITS, __SHIFTIN, __SHIFTOUT, __SHIFTOUT_MASK - macros for preparing bitmasks and operating on bit fields

SYNOPSIS



uint32_t __BIT(n)

uint32_t __BITS(m, n) __SHIFTIN(v, mask) __SHIFTOUT(v, mask) __SHIFTOUT_MASK(mask)

DESCRIPTION

These macros prepare bitmasks, extract bitfields from words, and insert bitfields into words. A ``bitfield'' is a span of consecutive bits defined by a bitmask, where 1s select the bits in the bitfield.

Use __BIT and __BITS to define bitmasks:

__BIT(n)
Return a bitmask with bit m set, where the least significant bit is bit 0.

__BITS(m, n)
Return a bitmask with bits m through n, inclusive, set. It does not matter whether m > n or m <= n. The least significant bit is bit 0.

__SHIFTIN(), __SHIFTOUT(), and __SHIFTOUT_MASK() help read and write bitfields from words:

__SHIFTIN(v, mask)
Left-shift bits v into the bitfield defined by mask, and return them. No side-effects.

__SHIFTOUT(v, mask)
Extract and return the bitfield selected by mask from v, right-shifting the bits so that the rightmost selected bit is at bit 0. No side-effects.

__SHIFTOUT_MASK(mask)
Right-shift the bits in mask so that the rightmost non-zero bit is at bit 0. This is useful for finding the greatest unsigned value that a bitfield can hold. No side-effects. Note that __SHIFTOUT_MASK(m) = __SHIFTOUT(m, m).

EXAMPLES

/*
 * Register definitions taken from the RFMD RF3000 manual.
 */
#define RF3000_GAINCTL          0x11            /* TX variable gain control */
#define         RF3000_GAINCTL_TXVGC_MASK       __BITS(7, 2)
#define         RF3000_GAINCTL_SCRAMBLER        __BIT(1)
        

/* * Shift the transmit power into the transmit-power field of the * gain-control register and write it to the baseband processor. */ atw_rf3000_write(sc, RF3000_GAINCTL, __SHIFTIN(txpower, RF3000_GAINCTL_TXVGC_MASK));

/* * Register definitions taken from the ADMtek ADM8211 manual. * */ #define ATW_RXSTAT_OWN __BIT(31) /* 1: NIC may fill descriptor */ /* ... */ #define ATW_RXSTAT_DA1 __BIT(17) /* DA bit 1, admin'd address */ #define ATW_RXSTAT_DA0 __BIT(16) /* DA bit 0, group address */ #define ATW_RXSTAT_RXDR_MASK __BITS(15,12) /* RX data rate */ #define ATW_RXSTAT_FL_MASK __BITS(11,0) /* RX frame length, last * descriptor only */

/* Extract the frame length from the Rx descriptor's * status field. */ len = __SHIFTOUT(rxstat, ATW_RXSTAT_FL_MASK);

HISTORY

The bits macros first appeared in atw(4), with different names and implementation. bits macros appeared with their current names and implementation in NetBSD4.0.

AUTHORS

The bits macros were written by David Young <dyoung@NetBSD.org>
. Matt Thomas <matt@NetBSD.org>
suggested important improvements to the implementation, and contributed the macro names SHIFTIN() and SHIFTOUT().

BUGS

__BIT() and __BITS() can only express 32-bit bitmasks.