Command        Operation
-------        ---------
tr_addrequest  request that the timer device wait a specified period of
               time before replying to the request.

tr_getsystime  get system time and place in a timeval structure.

tr_setsystime  set the system time from the value in a  timeval structure.


Device Functions
----------------
addtime()      add one  timeval structure to another.  the result is placed
               in the first timeval structure.

cmptime()      compare one  timeval structure to another.  the result is
               returned as a longword.

getsystime()   get system time and place in a  timeval structure.

readeclock()   read the current 64 bit value of the e-clock into an
               eclockval structure.  the count rate of the e-clock is also
               returned. (V36)

subtime()      subtract one timerequest structure from another. the result
               is placed in the first timerequest structure.


Exec Functions as Used in This Chapter
--------------------------------------
abortio()      abort a command to the timer device.

checkio()      return the status of an i/o request.

closedevice()  relinquish use of the timer device. all requests must be
               complete before closing.

doio()         initiate a command and wait for completion (synchronous
               request).

opendevice()   obtain use of the timer device.  the timer device may be
               opened multiple times.

sendio()       initiate a command and return immediately (asynchronous
               request).


Exec Support Functions as Used in This Chapter
----------------------------------------------
createextio()  create an extended i/o request structure of type
               timerequest.  this structure will be used to communicate
               commands to the timer device.

createport()   create a signal message port for reply messages from the
               timer device.  Exec will signal a task when a message
               arrives at the reply port.

deleteextio()  delete the timerequest extended i/o request structure
               created by createextio().

deleteport()   delete the message port created by createport().