SPRUJ79 November 2024 F29H850TU
The SSU is tightly coupled with each CPU during different phases of execution. When the CPU requests an instruction fetch, the SSU first decodes the instruction address to a LINK, STACK, and ZONE, and passes that information back to the CPU along with the fetched data. The CPU retains this security context information together with the instruction throughout the execution pipeline, and passes the context along to the SSU when making a data memory read or write access. Within the SSU, the data access filter logic uses the LINKID and CLINK associated with the instruction to qualify each memory access request and determine whether to permit the access.
The SSU provides a CPUID register, can be read by the application to determine which CPU the application is executing on. Additionally, the decoder logic can be used to determine which LINK, STACK and ZONE a particular code instruction belongs to, by writing the instruction's address to the DECODER_ADDR_IN register and reading the DECODER_OUT register.
Figure 10-4 illustrates the tightly-coupled interface between the SSU and the C29x CPU.