[Open-graphics] Video interrupt enable/disable

[James Richard Tyrer]

Timothy Normand Miller wrote:
> On 4/18/07, James Richard Tyrer <tyrerj at acm.org> wrote:
>> Paul Brook wrote:
>> > Really? I'd expect everything to be a single PCI device. DMA 
>> controllers only
>> > tend to exist as separate entities on systems where the normal 
>> devices can't
>> > be bus-masters. You may implement it as a separate functional block 
>> in the
>> > FPGA, but the host system doesn't know or care about that.
>> >
>> And exactly how will the host system determine if two interrupts come
>> from one device or from two separate devices?
> 
> If two interrupts come from one device, then it's really only one
> interrupt.  The driver should detect that its device has more than in
> interrupt condition asserted and process both.
> 
> If two interrupts come from two devices... The ISR for one device
> processes its interrupt and clears the condition.  Generally, it'll
> inform the kernel that it claimed the interrupt, so the kernel will
> just return from the interrupt handler.  However, the signal will
> still be asserted on the bus, causing the CPU to be interrupted again
> after processing the RTE instruction.  The process of finding the
> driver to claim the interrupt starts again, and then the second driver
> claims it.
> 
Actually, this was just a rhetorical question. ;-|

But I guess that the Kernel does know because device drivers register 
their interrupts with the Kernel.

-- 
JRT