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Next gen wireless apps with FRAM-based MCUs

Posted: 14 May 2012 ?? ?Print Version ?Bookmark and Share

Keywords:embedded wireless? ferroelectric random access memory? microcontroller?

Universal memory allows for fluid transition from program to data, but it also opens the door for potential memory confusion and corruption. Since data and program memories are interchangeable, care must be taken to ensure that access to dedicated regions in memory are protected and validated. Access control as well as boundary and range checking are all well-known practices in embedded firmware design and the process is rather straightforward when developing a single static firmware. However, these rules and settings become harder to track when memory requirements can change dynamically, transitioning between firmware versions. This is especially true, when coupled with over-the-air updates that can significantly change many aspects of the applications. Fortunately, FRAM MCUs usually offer memory protection, access control and memory protection features to organize and enforce such rules and settings. It is important for and suggested that firmware developers take full advantage of these features to ensure robust and reliable applications.

Low-power and high-speed write opens a new dimension of flexibility for data-logging applications

In a wireless application optimized for low power, the structure and method of data logging can heavily influence the power efficiency of the system. It is well understood that radio operation typically dominates the power budget of a wireless system; common sense suggests that power can be reduced by minimizing the duty cycle of the radio, or, the duration that the radio must stay in active mode.

The overhead associated with each radio transmission, however, is often the unnoticed power-hungry activity. This includes, turning on the radio core, ramping up the power supply, calibrating the oscillator and frequency generator as well as the power consumed during transitions from different radio states. Therefore, it is also necessary to minimize the frequency between data transmission C basically, record as much data as possible before commencing the next radio operation. The limit for this type of power optimization is the size of storage memory available on the MCU. With the traditional model of ratio-based, Flash-RAM memory configuration, some might say the answer is the maximum size of Flash available on the MCU.

This does offer a significant data storage option, but also presents higher power consumption for Flash write operations and speed limitations due to extremely slow Flash writes. On the other hand, RAM is much faster, does consume less power and is offered in a larger size in some MCU platforms. Unfortunately, the high premium of RAM can quickly drive up the cost of the system. Moreover, the volatile nature of RAM does not play well with systems that have "inconsistent" power supplies, such as those found in energy-harvesting applications. The model's susceptibility to data loss forces the system to either tolerate data loss or increase the frequency of data transmission and radio operations.

Figure 3: Memory Low-power and high-speed write with FRAM.

Once again, having the best of both worlds with low-power writes as well as non-volatile memory, FRAM can solve the problems that neither of the traditional memory technologies addresses. Figure 3 illustrates both such dimensions.

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