Manual Pages for UNIX Operating System command usage for man drv_usectohz

Kernel Functions for Drivers                     drv_usectohz(9F)



NAME
     drv_usectohz - convert microseconds to clock ticks

SYNOPSIS
     #include 
     #include 



     clock_t drv_usectohz(clock_t microsecs);


INTERFACE LEVEL
     Architecture independent level 1 (DDI/DKI).

PARAMETERS
     microsecs    The number of microseconds to convert.


DESCRIPTION
     The  drv_usectohz()  function  converts  a  length  of  time
     expressed in microseconds to a number of system clock ticks.
     The  time  arguments  to  timeout(9F)  and   delay(9F)   are
     expressed in clock ticks.


     The drv_usectohz() function  is  a  portable  interface  for
     drivers  to  make  calls  to  timeout(9F)  and delay(9F) and
     remain binary compatible should the driver  object  file  be
     used  on  a system with a different clock speed (a different
     number of ticks in a second).

RETURN VALUES
     The value returned is  the  number  of  system  clock  ticks
     equivalent  to  the  microsecs  argument.  No error value is
     returned. If the clock tick equivalent to microsecs  is  too
     large  to  be  represented  as  a  clock_t, then the maximum
     clock_t value will be returned.

CONTEXT
     The drv_usectohz() function can be called from user,  inter-
     rupt, or kernel context.

SEE ALSO
     delay(9F), drv_hztousec(9F), timeout(9F)


     Writing Device Drivers

NOTES
     If the microsecs argument to  drv_usectohz()  is  less  than
     drv_hztousec(9F),  drv_usectohz()  returns  one  tick. This,



SunOS 5.11          Last change: 24 Apr 2008                    1






Kernel Functions for Drivers                     drv_usectohz(9F)



     coupled with multiplication,  can  result  in  significantly
     longer  durations  than  expected. For example, on a machine
     where hz is 100, calling  drv_usectohz()  with  a  microsecs
     value  less  than 10000 returns a result equivalent to 10000
     (1 tick). This type of mistake causes code  such  as"5000  *
     drv_usectohz(1000)"  to  compute  a  duration  of 50 seconds
     instead of the intended 5 seconds.
















































SunOS 5.11          Last change: 24 Apr 2008                    2