[Open-graphics] Video interrupt enable/disable

[James Richard Tyrer]

Timothy Normand Miller wrote:
> On 4/16/07, James Richard Tyrer <tyrerj at acm.org> wrote:
> 
>> I'm not a PCI expert.  However, you are talking about the actual
>> physical implementation in PCI.  If masking is required, this would be a
>> function in the PCI interface.  However, IIUC, PCI devices are allowed
>> multiple interrupts -- each PCI device is allowed to use all 4
>> interrupts.  If they share common physical interrupt lines, this is an
>> issue with the PCI interface hardware and driver.
> 
> We'll use a single interrupt line.  Multiple conditions could cause
> the interrupt line to be signaled, but we'll just read a status
> register to find out which ones happened.
> 
> In general, computers have a limited number of interrupt lines anyhow,
> so what the OS will do is call into your kernel driver, asking you if
> this is your interrupt.  If it is, you service it and return a flag,
> indicating that you have claimed it.  If not, you return a different
> flag, and the kernel keeps trying other drivers.  If more than one
> device asserted the same line, then upon return from the ISR, the
> interrupt will happen again, and the process starts over.  It's very
> important to clear your interrupt conditions before existing your ISR
> so that you don't cause spurrious interrupts.
> 
Have I been the victim of Intel hype?  They make hardware that would 
make it possible to have enough interrupts for each PCI card slot to 
have 4 interrupts or at least to have 24 hardware interrupts available 
to be assigned with a cross point.

-- 
JRT