A device can have a maximum of four SLRs. The BootROM on secondary SLRs expects the boot PDI from PLM running on the primary SLR, which is loaded via the NoC and SBI interface.
The final PDI to boot on a device built using SSI technology is a PDI of PDIs which means that the PDI of each SLR is integrated in the main PDI. All the SLRs are chained. SLR0 which is also called the primary SLR is the bottom die. Secondary SLR1 is second from bottom, secondary SLR2 is third from bottom, and secondary SLR3 is the top SLR as shown in the following figure. So, the secondary SLR(n) must be booted. A full or partial NoC configuration should be performed before the secondary SLR(n+1) can be booted. In the following figure, the red lines are configured by BootROM, blue lines are configured by Boot PDI, and the black lines are hardened.
The boot flow for SSI devices is as follows:
- The PLM runs the PMC CDO on the primary SLR.
The subsystem boot master configuration for all SLRs is as follows:
- PLM runs the SLR Boot CDO to configure the NoC path from primary SLR to SLR1.
- PLM sends SLR1’s initial boot PDI to SLR1 and waits until PLM on SLR1 runs and configures the NoC path from SLR1 to SLR2.
- PLM sends SLR2’s initial boot PDI to SLR2 and waits until the PLM on SLR2 runs and configures the NoC path from SLR2 to SLR3.
- PLM sends the SLR3’s initial boot PDI to SLR3 and waits until the PLM on SLR3 runs.
- Once all SLRs are up and running, PLM on all SLRs configures the user-defined NoC frequency at the same time.
- PLM on the primary SLR loads other images present in the boot PDI such as LPD
The Primary configuration for all SLRs is as follows:
- The main PDI can also contain the PL configuration of all SLRs to be executed once all the SLRs are booted. The PL configuration of the secondary SLR is a partial PDI which is included in the main PDI.
- The PLM running on the primary SLR sends the configuration PDI of secondary SLRs via the same secondary's SBI interface and waits for the synchronization from all secondary SLRs to know that the configuration is complete.