Visible to Intel only — GUID: nik1410905665972
Ixiasoft
Visible to Intel only — GUID: nik1410905665972
Ixiasoft
8.1.1. MSI and Legacy Interrupts
- The MSI Capability registers
- The traffic class (app_msi_tc)
- The message data specified by app_msi_num
The Application Layer Interrupt Handler Module also generates legacy interrupts. The app_int_sts signal controls legacy interrupt assertion and deassertion.
The following figure illustrates a possible implementation of the Interrupt Handler Module with a per vector enable bit. Alternatively, the Application Layer could implement a global interrupt enable instead of this per vector MSI.
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.
The following table describes three example implementations. The first example allocates all 32 MSI messages. The second and third examples only allocate 4 interrupts.
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. In other words, the earliest that app_msi_req can deassert is on the rising edge of clock cycle 5 (one cycle after app_msi_ack is asserted) as shown, but it can deassert in later clock cycles as well.