Vulnerability - janomach/the-hardisc GitHub Wiki

Single point of failure (SPOF)

The execution pipeline is inherently protected by replication until the final write to the general purpose registers file (GPR) in the WB stage. The ACM manages writes via a single write port, consisting of:

1. write-enable (1 bit)
2. write-address (5-bit)
3. data (32-bits)
4. checksum (7-bits)

The write-port signals are protected via the TMR modules, which select the majority value from the input to the output (bitwise). But, the TMR modules are not replicated, creating a SPOF. Since the data and checksum create a code word with error detection and correction capability, faults in the TMR modules selecting those signals are not an issue (unless there are more than two faults). The signals write-enable and write-address do not contain additional protection. The GPR is clocked by a single clock signal, creating another SPOF. Protection of those three signals (write-enable, write-address, clock) should be addressed at the physical level.