[ixp1200] How to signal from Pentium to IXP EB?

Hello. I use IXP1200 EB attached(on PCI slot) to Pentium PC. How can I signal from Pentium PC to MICROENGINE in IXP EB? I searched VERA code to find the method. But I failed to find until now. Is there a good method? Like using some register or using interrupt? I think "polling" method now. Namely, PC writes a flag into SDRAM or SRAM region and MicroEngine check that flag continually. But I think that interrupt is more polished method. ^^ Plz give me any method about signalling from PC to IXP EB. Peformance is most important for my application. Thanks!