Topic       : TOS - The Operating System
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View Ref-File11.5.16.39.26  mxk_evnt_IO                                         TOS

 Name:        »evnt_IO«

 Parameters:

               d0 =  long ticks_50hz
               a0 =  void *unsel

 Description: mxk_evnt_IO makes it possible to wait for one external 
              event. The external event in question is either an 
              interrupt or another application (which perhaps writes 
              to a pipe for awakening). The function is used for the 
              creation of device drivers:

              Procedure (see DEV_LPT1 as an example):

                1. Block interrupts.
                2. Inquire whether the event (in the case of DEV_LPT1 
                   the event is called: 'Centronics busy off') has 
                   arrived.
                3. If so, free interrupts and perform the action (in 
                   the case of DEV_LPT1: print character).
                4. If not, set up interrupt routine (in the case of 
                   DEV_LPT1: MFP-I0, i.e. 'Activate Centronics busy 
                   interrupt') and make available to it the current 
                   application (act_appl) and also a LONGword address 
                   into which the interrupt routine can write return 
                   messages. This address should have written to it 
                   the address of a routine that deinstalls the 
                   interrupt again, and can be followed by some user 
                   requirements. i.e. some further data. The unselect 
                   routine later gets a pointer to all this data and 
                   can evaluate the optional parameters for instance. 
                   The whole mechanism is required to guarantee a 
                   corrrect deinitialization of the interrupt in each 
                   case.
                5. Release interrupts.
                6. Call evnt_IO. In d0.w specify the number of 50Hz 
                   ticks for the timeout; 0 means 'no timeout'. In a0 
                   give the address of the LONGword containing the 
                   address of the clean-up routine that deinstalls the 
                   interrupt again (which is followed by optional 
                   further parameters, provided the unselect routine 
                   understands these). In the case of incorporation of 
                   device drivers for Fselect, only one optional 
                   LONGword is possible.
                   On arrival of the interrupt, the interrupt routine 
                   writes a status < 0L (error) or 1L (OK) in place of 
                   the deinitialization routine into the status 
                   LONGword (which previously contained its own start 
                   address). Following this the routine will deinstall 
                   itself or make sure that no actions are performed 
                   on following interrupts. Finally the interrupt 
                   routine awakens the application assigned to the 
                   interrupt, using the call appl_IOcomplete with the 
                   application as parameter.
                7. evnt_IO returns either the value 0L (timeout, the 
                   interrupt has not arrived) or < 0 (the interrupt 
                   has written an error-code to the status LONGword) 
                   or 1L (the interrupt has written a 1L into the 
                   status LONGword). Deinstallation of the interrupt 
                   is no longer required as the kernel has taken care 
                   of this if the interrupt routine did not do this 
                   itself on arrival of the interrupt.

 Group:       Kernel functions

 See also:    -