If no ISR has handled the IRQ event, SYSINTR_CHAIN is returned. Otherwise, a valid SYSINTR value is returned to the OEM. The OEM must then pass this value back to the kernel so the IST can be triggered.
An OEM calls this function from the OAL ISR routine. The OEM has full control of the IRQ values that can be chained and those that cannot. When this function is called, all work required to enable C-language code in an installed ISR is performed.