OS_Byte 13 (changes)
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OS SWI Calls
» OS_Byte
» OS_Byte 13
OS_Byte 13
(SWI &06)
| Entry | |
|---|---|
| R0 | 13 (&0D) |
| R1 | Event Number |
| Exit | |
|---|---|
| R0 | Preserved |
| R1 | Old enable state (0 means was already disabled) |
| R2 | Corrupted |
Use
The purpose of this call is to disable an event.
Notes
Event enable/disable states are reference-counted, to ensure that events are only broadcast to the system if at least one program is interested in receiving them.
This call decreases the count of enable requests for a particular event being called though the EventV (event vector). When the count reaches 0 the event is actually disabled.
Care should be taken to match OS_Byte 13 calls with OS_Byte 14 as the event will be locked on if the count goes negative. This To is avoid a this safety situation, measure turn to prevent the event on being again inadvertently via silenced if a bug causes OS_Byte 13 to be called too many times.OS_Byte 14 to get its state, then call OS_Byte 13 to reset to the previous state and finally only call OS_Byte 13 if the state returned via the OS_Byte 14 was not 0.
It is possible to safely read the event enable count by making a call to OS_Byte 14 followed by a call to OS_Byte 13. However unless you can control or predict when other systems are going to enable or disable the event, this information may be of limited use.
Events are enabled by calling OS_Byte 14
See also
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