A scan-chain based state retention methodology for IoT processors operating on intermittent energy

Abstract

Abstract-Future IoT systems are tightly constraint by cost and size and will often be operated from an energy harvester's output. Since these batteryless systems operate on intermittent energy they have to be able to retain their state during the power outages in order to guarantee computation progress. Due to the lack of large energy buffers the state needs to be saved quickly using residual energy only. In related work, the state is retained in-place by replacing all flip-flops with state retentive flip-flops (SRFF), which are powered by auxiliary supplies for retention or incorporate non-volatile memory cells. However, these SRFFs increase the power consumption during active operation impairing the overall systems efficiency. In this paper, we present a scan-chain based state retention approach, where the state is moved to memory using only 4.5pJ/b. Since our approach does not introduce any power overhead, this energy cost pays off after an on-time of just 100us compared to state-of-the-art inplace solutions. Moreover, compared to a software mechanism, our approach requires 6.6x less energy to move the state and is 5.8x faster.

Providing Confidentiality and Integrity in Ultra Low Power IoT Devices

“…In OoP techniques, which are the scope of this paper, the content of the CPU is moved towards an external retaining memory. OoP methods are generally preferred over InP because they require less design efforts and they consume less dynamic power [2]. Generally, using off-chip memories (e.g.…”

“…The power supply can be periodically monitored by specific software procedures that are generated in the compilation phase [7]. Alternatively, an interrupt mechanism can be employed, in order to trigger the context saving as soon as the supply voltage goes under a predefined threshold [2] [8]. The technique presented in [8] relies on interrupt routines that transfer the context to the NVM.…”

“…The technique presented in [8] relies on interrupt routines that transfer the context to the NVM. On the other side, the technique presented in [2] relies on a context saving procedure that is entirely managed at hardware level (i.e. the scan chain content is transferred to the NVM).…”

“…A recently proposed technique for context saving relies on the presence of scan chains inside the CPU [2]. Scan chains are always present inside microprocessor designs for testing purposes.…”

SI ECCS: SECure context saving for IoT devices

“…A common practice, called Context Saving, consists in saving the state of the device into a Non Volatile Memory (NVM) when the power supply cannot be guaranteed. The running process is resumed as soon as the energy is available by restoring the state from the NVM [1].…”