Message Signaled Interrupts

Message Signaled Interrupts, in PCI 2.2 and later and PCI Express, is an alternate form of interrupt from the traditional pin-signalled system; instead of asserting a given IRQ pin, a message is written to a segment of system memory. Each device can have from 1 to 32 unique memory locations (MSI, up to 2048 with the newer MSI-X standard) or in which to write MSI events to. An advantage of the MSI system is that data can be pushed along with the MSI event, allowing for greater functionality.

References

• The PCI 2.2 standard, section 6.8

External links

• MSDN paper on MSI in Windows Vista
• Linux MSI HOWTO
• Changes required to support MSI in FreeBSD (MSI / MSI-X Supported as of FreeBSD 6.3-RELEASE)
• Changes made to support MSI in Solaris Express
• Charlie Chen's Weblog: how does MSI-X work