[meta-xilinx] Interrupt forwarding in AMP configuration

[Eric Wong]

On Thu, Dec 22, 2016 at 3:38 PM, Eric Wong <ewong3 at gmail.com> wrote:
> The "4" in the interrupts line means the interrupt is active high, and
> things seem to be working.  If I want an interrupt to be rising edge
> triggered, I change the "4" to "1", but then when that interrupt
> triggers I get "Unexpected IRQ trap at vector 00" error in Linux and
> Linux freezes.  Does anyone know what that means or how to fix that
> error?  I would think Linux wouldn't/shouldn't even be looking at the
> interrupt(s) that are routed to CPU1.  Thanks in advance.

The interrupts in question are actually the FPGA fabric interrupts
from the PL to PS.  The Zynq only supports active high or rising edge
triggered interrupts, but it seems there is an additional requirement
that the interrupt line be idle low.  I can't seem to have the
interrupt line idle high and trigger from the trailing, rising edge of
a negative pulse. The interrupt line idling high causes all sorts of
havoc (such as the "Unexpected IRQ trap at vector 00" error). I don't
know if that's due to the Cortex-A9s, the Zynq or Linux.  When the
interrupt line idles low, the FPGA interrupts can trigger off the
leading, rising edge of a positive pulse just fine.