## 6 Multi-Core Hardware Platform for the Reliability Improvement  
In past research experience, it was proved that 30% to 50% Live nodes [37] failed after being deployed for two months, although these nodes worked properly for long periods when tested in the lab desktop. Since most WSN nodes are deployed in hostile environments where they are difficult to be brought back for repairing, the improvement of node reliability becomes a key research challenge. Currently in the MIROS, this multi-core hardware technology is also used to improve the node reliability. One way of using the multi-core hardware technology to improve the node reliability is the usage of the redundancy approach. For example, on the EMWSN node (Figure 14) the sensor peripherals can be managed by both the AVR core and the ARM core. Commonly, the AVR core is in charge of the sensor data collection work. In the case that the AVR core fails, the ARM core can substitute it to continue this task, thereby improving node reliability. In addition to the redundancy method, another way to improve the node reliability is to use a more reliable and ultra-low power core (management core) to manage a more powerful but less reliable and high power core (working core). Currently, this approach has been used on the multi-core node \(\mathrm{i}\mathrm{i}\mathrm{i}\mathrm{e}\mathrm{T}\). On the \(\mathrm{i}\mathrm{i}\mathrm{e}\mathrm{T}\), two cores are equipped: the 8-bit working core AVR ATmega1281 and the 4-bit management core nanoRisc. The AVR core is more powerful and can be used to perform WSN tasks, and MIROS runs on this core. The nanoRisc is low-end and cannot be competent for most WSN tasks. However, it is ultra-low power and highly reliable [38], and is thus ideal to be used as the management core to configure the work modes of the working core. The following is an example scenario: the working core AVR wakes up every six hours to collect the environmental data, and then transmit the data packet to the local server. To achieve this task, a periodical six-hour timer is set on the management core nanoRisc. Every time the periodical timer is fired, the power will be supplied to the AVR core. Once powered, the AVR core starts collecting the environmental data, and then sends a handshaking signal from the GPIO ports to the nanoRisc. If the handshaking signal is received by the nanoRisc within a given time, the AVR core can be powered off or fall asleep. If not, the exception may occur on the AVR core. In this case, the nanoRisc will restart the AVR core by the power control (power off first, and then power on again). In this manner, the reliability of the data collection task can be improved. The advantage of using this multi-core technology on the \(\mathrm{i}\mathrm{i}\mathrm{i}\mathrm{e}\mathrm{T}\) is that the reliability of the node will no longer be determined by the less reliable working core, but rather be determined by the highly reliable management core. In past experiments from two years ago, three single-core \(\mathrm{i}\mathrm{L}\mathrm{i}\mathrm{e}\mathrm{u}\mathrm{e}\mathrm{o} \mathrm{s}\mathrm{e}\mathrm{o}\mathrm{s}\) were deployed in the garden of ISIMA, and one of them failed only after working for two weeks. However, no nodes have failed thus far after the multi-core \(\mathrm{i}\mathrm{i}\mathrm{e}\mathrm{o}\mathrm{s}\mathrm{e}\mathrm{o} \mathrm{s}\mathrm{e}\mathrm{o}\mathrm{s}\) were applied (and have been working properly for more than two years; the environmental temperature ranges from \(-15\) degree to \(35\) degree). This result proves that the multi-core technology used on the \(\mathrm{i}\mathrm{i}\mathrm{i}\mathrm{e}\mathrm{T}\) is effective for reliability improvement. Besides the improvement to the node reliability, the multi-core technology can also decrease the energy consumption of the \(\mathrm{i}\mathrm{i}\mathrm{i}\mathrm{e}\mathrm{T}\) nodes.