SPRUJ28E November 2021 – September 2024 AM68 , AM68A , TDA4AL-Q1 , TDA4VE-Q1 , TDA4VL-Q1
In the case of MSI interrupts signaling, the interrupt conditions are communicated from the EP to the RP via messages. Thus, upon the occurrence of an interrupt condition, a message is sent by the EP with information that identifies the origin of the interrupt. Each message is in the form of a memory write request, containing an address and a data value to be written. Each PCI function supported by a device can be assigned a separate memory address, thus providing separate virtual channels for signaling interrupts generated by each function. In addition, the MSI mechanism allows a maximum of 32 distinct data patterns in the messages generated by each PCI function, and each pattern can be assigned to an interrupt condition within the function.
In the case of MSI-X interrupts signaling, the operation is similar to the MSI mode, except that the mechanism allows a much larger number of distinct interrupt conditions as many as 2048 per function to be communicated, and enables a distinct address to be defined for each of these conditions. This mechanism requires two tables to be stored in the EP memory. The MSI-X table contains the address/data patterns to be used for each interrupt condition (as many as 2048 per function) as well as individual enable/mask bits, and the Pending Bit Array (PBA) stores the status of each interrupt condition. Interrupt conditions are communicated from the EP to the RP via messages (write requests), as in the case of the MSI mode.