Provided by: freebsd-manpages_12.2-1_all bug


     mk48txx — Mostek time-of-day clock driver


     #include <sys/eventhandler.h>
     #include <sys/lock.h>
     #include <sys/mutex.h>
     #include <dev/mk48txx/mk48txxvar.h>

     To compile this driver into the kernel, place the following line in your kernel
     configuration file:

           device mk48txx


     The mk48txx driver is a back-end for several models of Mostek time-of-day clock chips.  It
     provides access methods to retrieve and set date and time for use with the “clock” KOBJ

     To tie an instance of this device to the system, use the mk48txx_attach() function and the
     mk48txx_softc structure defined as follows:

     int mk48txx_attach(device_t dev)

     typedef uint8_t (*mk48txx_nvrd_t)(device_t dev, int off);
     typedef void (*mk48txx_nvwr_t)(device_t dev, int off, uint8_t v);

     struct mk48txx_softc {
             struct resource sc_res;
             struct mtx      sc_mtx;
             eventhandler_tag        sc_wet;
             const char      *sc_model;
             bus_size_t      sc_nvramsz;
             bus_size_t      sc_clkoffset;
             u_int           sc_year0;
             u_int           sc_flag;
             mk48txx_nvrd_t  sc_nvrd;
             mk48txx_nvwr_t  sc_nvwr;

     sc_res  The bus resource used for accessing the chip's non-volatile memory (including the
             clock registers), which must be supplied by the front-end when using the default
             access methods (see below).  Otherwise this member is optional.

     sc_mtx  The hardware mutex used when accessing the chip's non-volatile memory (including the
             clock registers), which must be initialized with MTX_DEF by the front-end.

     sc_wet  The event handler tag for the watchdog functionality, which is registered by the
             mk48txx_attach() function if supported by the chip and specified as part of the
             machine-dependent features (see below).

             The chip model which this instance should serve.  This member must be set to one of
             “mk48t02”, “mk48t08”, “mk48t18”, or “mk48t59” by the front-end.

             The size of the non-volatile RAM in the Mostek chip, which is set by the
             mk48txx_attach() function.

             The offset into the control registers of the Mostek chip, which is set by the
             mk48txx_attach() function.

             The year offset to be used with the ‘year’ counter of the clock, which must be set
             by the front-end.  This value is generally dependent on the system configuration in
             which the clock device is mounted.  For instance, on Sun Microsystems machines the
             convention is to have clock's two-digit year represent the year since 1968.

             This flag is used to specify machine-dependent features.  The following flags are

             MK48TXX_NO_CENT_ADJUST   If the resulting date retrieved with the “clock_gettime()
                                      method” would be earlier than January 1, 1970, the driver
                                      will assume that the chip's year counter actually
                                      represents a year in the 21st century.  This behavior can
                                      be overridden by setting this flag, which causes the
                                      mk48txx driver to respect the clock's century bit instead.

             MK48TXX_WDOG_REGISTER    When this flag is set, the mk48txx driver will register as
                                      a watchdog via the interface defined in watchdog(9) if
                                      supported by the specific chip model.

             MK48TXX_WDOG_ENABLE_WDS  When this flag is set, the mk48txx driver will set the
                                      watchdog steering (WDS) bit when enabling the watchdog
                                      functionality of the chip.  enabled (see the chip
                                      documentation for further information regarding the WDS


             These members specify the access methods for reading respectively writing clock
             device registers.  The default, when NULL is passed as an access method, is to
             access the chip memory (and clock registers) as if they were direct-mapped using the
             specified bus resource.

             Otherwise, the driver will call the respective function supplied by the front-end to
             perform the access, passing it the offset off of the chip memory (or clock register)
             location to be read from or written to, respectively.


     The following models are supported:

           Mostek MK48T02
           Mostek MK48T08
           Mostek MK48T18
           Mostek MK48T59


     intro(4), watchdog(9)


     The mk48txx driver appeared in NetBSD 1.5.  The first FreeBSD version to include it was
     FreeBSD 5.0.


     The mk48txx driver was written for NetBSD by Paul Kranenburg <>.  It was ported
     to FreeBSD by Thomas Moestl <> and later on improved by Marius Strobl