Self-timed is self-checking

Yield enhancement of asynchronous logic circuits through 3-dimensional integration technology

“…Due to the multi-rail encoded data and explicit handshake-based event-ordering, the authors in [3] proved that any failure by a single stuck-at fault in the PCHB circuit either deadlocks the circuit or produces an illegally encoded output (X 0 X 1 ='11'). Thus, fail-stop behavior can be implemented by adding a checker (NAND gate) onto each output of a PCHB circuit which blocks the incoming handshake signals in the presence of any illegal output.…”

Efficient failure detection in pipelined asynchronous circuits

“…Failure detection is then achieved by deadlock recognition logic. Unlike previous researches [2,4,14,15,18,19], both permanent and transient faults can be detected by this method, while no significant timing assumption is required. We first explain that widely-used QDI circuit template, and then present the fault model based on the conclusions in Section 2.…”

“…The authors in [2] and [19] proved that any single stuck-at fault in a PCHB-like circuit either deadlocks the circuit or throws an illegally dual-rail encoded output ('11'). By checking unacceptable data token on each output channel before receiving the incoming acknowledge, we can easily make the circuit also deadlock in the presence of any illegally encoded output from current process.…”

“…Proof: According to the HSE statement (2), all signals in a FS-PCHB circuit other than those of pull-down stacks in computational module and the inputs/outputs of I-elements, must enable both up and down transitions in order to complete the handshake sequence. If any of such signals get stuck, the communication between current and neighbor pipeline stages cannot move forward and the whole pipeline deadlocks.…”

“…David et.al. [2] and Yang [19] investigated stuck-at fault detection in dynamic asynchronous circuits, and proposed the self-checking clockless designs with respect to hard errors. Hyde et.al.…”