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ANALOG & MIXED SIGNAL equivalent to about 100 lines of standard C code written for common 8 and 16-bit MCUs. As the name implies an ASM has no clock and is event driven, which means that when there are no events, the ASM stays in one state and consumes no static power. Thus, applications with limited input cycles can operate at leakage current power consumption well in to the single digit nanoamps of average current consumption at room temperature. Handing embedded control problems Typical embedded control problems usually involve a system that is transitioning through a set of discrete states based on asynchronous external inputs. ASMs are the natural problem solver for this. Silego has revived and modernized the ASM, mitigating the well-known hazard and race conditions, the programming/configuration headaches, while retaining all the inherent low-power, low-latency benefits for simple (up to 8 states) embedded control problems that would require less than 100 lines of code. Over kill microcontrollers v. CMIC ASM value Microcontrollers contain a processor, program code, stack memory, and various peripherals. Microcontrollers can easily perform the application examples above but are inefficient in size and power. It is quite common to find MCUs designed into applications where less than 1% of the MCU horsepower will ever be used. A device such as a CMIC’s ASM is well suited to simple embedded control applications, especially ultra-lower power applications. Interrupt latency down to nanoseconds Designing a state machine on a microcontroller is typically done in software running on the microcontroller core. In this case, the states are implemented as points in the software instruction The GreenPack CMIC block diagram. execution, and state transitions are implemented with conditional software branching. Microcontrollers have the capability to also process asynchronous inputs, and they do this through dedicated interrupt controller hardware, and through interrupt service routines (ISRs). The ISR is software that is run after a hardware interrupt has been activated. An important benchmark for microcontrollers is how short the time from an external interrupt signal is until the core is executing the first instruction of the ISR, the so-called interrupt latency. MCU interrupt latency in general purpose devices is usually measured in fast examples at around 5 to 10 microseconds. An ASM equivalent of interrupt latency is measured in nanoseconds Silego Technology’s GreenPAK Designer development software. – equivalent to the unclocked time of flight through the few gates between an external pin and the internal ASM input. The ASM has latency from one state to the next. If the CMIC is operating at a 5V power supply, the latency is a maximum of 50ns. Yes, ASMs are extremely fast and extremely low power. VDD variation
A CMIC ASM works over a wide voltage range. A properly designed ASM is guaranteed hazard and race condition free because each ASM signal path is guaranteed by signal length and gate count. Thus, as the VDD changes, so does the propagation delay. However, the propagation delays are all matched and thus performance is guaranteed. Microcontrollers, on the other hand, are clocked with signals that are not correlated well with VDD. As the VDD changes, the MCU propagation delays change and since the timing doesn’t change, the timing margins are soon compromised. Chip designs react to these design hazards but putting the MCU under a voltage regulator or requiring still more performance to be lost by slowing the clock speed. However, the voltage regulator consumes power, and the slower clock speed increases interrupt latency. Crash versus no crash Design and system flaws can cause a microcontroller to crash. Poorly written software, timing issues, miscalculations of interrupt latency, running out of stack memory, memory leakages, and accidental writes in program memory are some common pitfalls that cause MCUs to crash. Silego’s ASM is configured in hardware with NVM bits, has no timing issues, latency measured in nanosecond, no stack memory, no ability for memory leakage, and no ability to unintentionally over write program memory, and is therefore inherently more robust with VDD noise and brownouts. No code GUI based tools versus typical MCU tools A CMIC ASM is configured using the GreenPAK Designer development environment. The software appears to be a schematic capture editor instead of a coding tool. Most state machine designs can be implemented in a matter of minutes reducing the typical MCU tool learning curve from months to Silego’s GPAK learning curve of a few days. In summary, a tiny CMIC with a 8 state ASM can take on a variety of embedded control applications that would formerly have been the exclusive domain of microcontrollers. The easily configured ASM brings key advantages of ultra-fast state transitions, leakage level static current consumption, robust design, and supply voltage tolerance so important in IoT, portable, mobile and embedded applications. In addition, CMICs offer many benefits that will make embedded designers’ work easier and their products more profitable. They are the ideal solution because board space is tight and needs to be maximized to save space for other valuable functions (such as a bigger battery). They also make procurement happy by saving significantly over traditional analog and discrete while dramatically reducing the risk and stress involved. www.electronics-eetimes.com Electronic Engineering Times Europe March 2017 27


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