MSI support? #616
Description
It is possible to support message-signaled interrupts in the same way as the IMSIC, with the addition of
- memory mapped MSI receiving locations as described in the the AIA
- introduce an encoding (value = 2) for xaclicsourcecfg[N].SM (source mode) that indicates that the interrupt has an MSI source.
Setting a default of 2 for xaclicsourcefg[N].SM would result in the composite MSI-enabled ACLIC controller coming out of reset functionally identical to an IMSIC. [eidelivery does not need an ACLIC option]
APLIC is really designed to work in conjunction with an IMSIC (direct delivery to CLINT is described in AIA notes as "maybe software would want to do this" & sounds like it is more for PLIC compatability than anything else).
Therefore an MSI-enabled ACLIC provides both IMSIC compatability and APLIC connectivity (APLIC interfaced via MSI).
Note: interrupts that are configured to have an MSI source receive their priority via MSI; priority configured in xacliciprio is not used.