The VCAM VME Controller places an interrupt request to a specific CPU on the POWERpath-2 bus. The destination CPU records the interrupt in its interrupt register and, if interrupts at that level are not masked off, it responds by trapping to an interrupt vector.
The time taken for these events is the hardware latency, or interrupt propagation delay. The typical propagation delay is 2 microseconds. The theoretical worst-case delay is 8 microseconds, but this requires a very large system configuration. For typical configurations, 4 microseconds is an appropriate estimate of worst-case delay.
The worst-case hardware latency can be significantly reduced by not placing either graphics or HIPPI interfaces on the POWERchannel-2 interface used for VME devices.