Altera Arria V Avalon-ST - Manual (Page 121)

There are 32 possible MSI messages. The number of messages requested by a particular component does
not necessarily correspond to the number of messages allocated. For example, in the following figure, the
Endpoint requests eight MSIs but is only allocated two. In this case, you must design the Application
Layer to use only two allocated messages.
Figure 7-3: MSI Request Example
Endpoint
8 Requested
2 Allocated
Root Complex
CPU
Interrupt Register
Root
Port
Interrupt
Block
The following table describes three example implementations. The first example allocates all 32 MSI
messages. The second and third examples only allocate 4 interrupts.
Table 7-1: MSI Messages Requested, Allocated, and Mapped
MSI
Allocated
32 4 4
System Error 31 3 3
Hot Plug and Power
Management Event
30 2 3
Application Layer 29:0 1:0 2:0
MSI interrupts generated for Hot Plug, Power Management Events, and System Errors always use Traffic
Class 0. MSI interrupts generated by the Application Layer can use any Traffic Class. For example, a DMA
that generates an MSI at the end of a transmission can use the same traffic control as was used to transfer
data.
The following figure illustrates the interactions among MSI interrupt signals for the Root Port. The
minimum latency possible between
app_msi_req
and
app_msi_ack
is one clock cycle. In this timing
diagram
app_msi_req
can extend beyond
app_msi_ack
before deasserting. However,
app_msi_req
must
2014.12.15
MSI Interrupts 7-3
Interrupts Altera Corporation
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