Cause: cause a software interrupt

Cause(interrupt)

A1

void Cause(struct Interrupt *);

This function causes a software interrupt to occur. If it is called from user mode (and processor level 0), the software interrupt will preempt the current Task. This call is often used by high-level hardware interrupts to defer medium-length processing down to a lower interrupt level. Note that a software interrupt is still a real interrupt, and must obey the same restrictions on what system function it may call.

Currently only 5 software interrupt priorities are implemented: -32, -16, 0, +16, and +32. Priorities in between are truncated, values outside the -32/+32 range are not allowed.

When setting up the Interrupt structure, set the node type to NT_INTERRUPT, or NT_UNKNOWN.

IMPLEMENTATION

1> Checks if the node type is NT_SOFTINT. If so does nothing since

the softint is already pending. No nest count is maintained.

2> Sets the node type to NT_SOFTINT.

3> Links into one of the 5 priority queues.

4> Pokes the hardware interrupt bit used for softints.

The node type returns to NT_INTERRUPT after removal from the list.

interrupt: pointer to a properly initialized interrupt node

Unlike other Interrupts, SoftInts must preserve the value of A6.

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