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 cia.resource
  AbleICR
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Docs » Autodocs » cia.resource » AddICRVector

NAME

	AddICRVector -- attach an interrupt handler to a CIA bit.

SYNOPSIS

	interrupt = AddICRVector( Resource, iCRBit, interrupt )
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struct Interrupt *AddICRVector( struct Library *, WORD,
struct Interrupt * );

FUNCTION

	Assign interrupt processing code to a particular interrupt bit
of the CIA ICR. If the interrupt bit has already been
assigned, this function will fail, and return a pointer to the
owner interrupt. If it succeeds, a null is returned.
This function will also enable the CIA interrupt for the given
ICR bit.

INPUTS

	iCRBit          Bit number to set (0..4).
interrupt Pointer to interrupt structure.

RESULT

	interrupt       Zero if successful, otherwise returns a
pointer to the current owner interrupt
structure.

NOTES

	A processor interrupt may be generated immediately if this call
is successful.
In general, it is probably best to only call this function
while DISABLED so that the resource to which the interrupt
handler is being attached may be set to a known state before
the handler is called. You MUST NOT change the state of the
resource before attaching your handler to it.
The CIA resources are special in that there is more than one
of them in the system. Because of this, the C language stubs
in amiga.lib for the CIA resources require an extra parameter
to specify which CIA resource to use. The synopsis for the
amiga.lib stubs is as follows:
interrupt = AddICRVector( Resource, iCRBit, interrupt )
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struct Interrupt *AddICRVector( struct Library *, WORD,
struct Interrupt *);
***WARNING***
Never assume that any of the CIA hardware is free for use.
Always use the AddICRVector() function to obtain ownership
of the CIA hardware registers your code will use.
Note that there are two (2) interval timers per CIA. If
your application needs one of the interval timers, you
can try to obtain any one of the four (4) until AddICRVector()
succeeds. If all four interval timers are in-use, your
application should exit cleanly.
If you just want ownership of a CIA hardware timer, or register,
but do not want interrupts generated, use the AddICRVector()
function to obtain ownership, and use the AbleICR() function
to turn off (or on) interrupts as needed.
Note that CIA-B generates level 6 interrupts (which can degrade
system performance by blocking lower priority interrupts). As
usual, interrupt handling code should be optimized for speed.
Always call RemICRVector() when your code exits to release
ownership of any CIA hardware obtained with AddICRVector().

SEE ALSO

cia.resource/RemICRVector(), cia.resource/AbleICR()

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