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Redundant computing Lockstep systems circuit

2017-01-06 08:02  
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Lockstep systems are redundant computing systems that run the same set of operations at the same time in parallel. The output from lockstep operations can be compared to determine if there has been a fault. Sometimes a timeshift (delay) is set between two systems, which increases the detection probability of errors induced by external influencesThis hardware-software combination deletes clocks from the slave until both /iPs synchronize. The firmware loop causes each to generate a WR signal once per loop. The circuit exclusive-ORs the two WR signals to produce a miss-compare pulse. The miss-compare pulse latches into the two JK flip-flops via outputs LOCKSTP1 and LOCKSTP2. A high on these signals indicates that the /tPs are in lock-step, causing both juPs` programs` execution to exit the firmware loop. If you use discrete components, you`ll probably want to use the Q output of the JK flip-flop and delete the circuit`s inverters. The listing uses the /iPs` ports 1 and 3. You cannot use a memory-mapped location for the lock-step-detect clear (K input) because this scheme would generate additional WR signals. You could apply this idea to other, perhaps using their RD signals. This way, generating anRD signal to activate the lock-step-detect clear would not affect the synchronization inputs.
To run in lockstep, each system is set up to progress from one well-defined state to the next well-defined state. When a new set of inputs reaches the system, it processes them, generates new outputs and updates its state. This set of changes (new inputs, new outputs, new state) is considered to define that step, and must be treated as an atomic transaction; in other words, either all of it happens, or none of it happens, but not something in between.The term "lockstep" originates in the prison usage, where it refers to the synchronized walking, in which the marchers walk as closely together as physically practical.

 

Dual 8051S Execute In Lock-Step