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     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 interface.

     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

             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 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 supported:

             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 9(watchdog) 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 bit).


             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

             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