A competition among MCU manufacturers to advance into low power consumption: ULPBench becomes the starting point

Click EEWORLD to follow the world of electronic engineering

We regularly push the hot topics in the industry that you care about most, hot forum posts and exciting discussions, and many other high-quality content. There are also more exciting activities waiting for you to participate! It’s a good idea to follow us!

A series of new product launches recently have shown us the latest development trend of the microcontroller industry, which is to cater to the power supply industry and mobile device market that are closely linked to the Internet of Things and are developing rapidly. Based on the ULPBench power standard proposed by the EEMBC Association last year, MCU manufacturers have actively participated in this leap forward game, and new products have continuously refreshed test results, and the industry's leadership position has also been constantly changing.

This series of reactions is very much like a market game. When manufacturers need to improve their own technology to save power consumption, developers will become the final winners.

In the past, low-power MCUs often meant low performance, but manufacturers are working to challenge this relationship by providing increasingly powerful MCUs to accommodate low-power applications. However, developers are faced with the problem of how to evaluate the results of MCU manufacturers. Traditional specifications, such as operating current in mW/MHz, leakage current in sleep mode, and when the device has multiple power states, such evaluations are stretched. At the same time, in the industrial field, the descriptions and rules for low-power operation are often inconsistent.

In addition, many applications require long sleep periods with fast response times. For such devices, parameters such as wake-up time and the time required to execute a response before returning to sleep will seriously affect the total energy consumption in actual applications. These factors will have a serious impact on the accuracy of testing the power consumption of low-power components.

The ULPBench standard was first released at the EEMBC Association in March 2014. Its consistent goal is to provide developers with a reliable and reasonable MCU energy efficiency measurement method. Last October, ULPBench and the standard hardware measurement platform EnergyMonitor were publicly discussed and then merged into a new test standard that MCU developers have been promoting.

In an interview with reporters, Marcus Levy, chairman of EEMBC, said, "The ULPBench standard is one of the most accurate standards to date." This standard will perform 20,000 clock cycles on the MCU in one second and put it into sleep mode for the rest of the time. This method makes each processor perform the same amount of work, making the environment for executing the standard the same.

The final score is expressed as 1000 divided by the middle value in every 10 standard cycles, and finally the average power consumption is obtained. Therefore, the larger the number, the lower the power consumption.

The ULPBench power value of the EEMBC Association is measured by measuring the MCU core processor in a series of sleep-process-sleep cycles.

Recently, MCU manufacturers have begun to publish a series of test results based on this standard, and have taken turns to temporarily take the lead. It all started when STMicroelectronics released its STM32L4 microcontroller family in mid-February. A week later, this product based on the ARM Cortex-M4 processor scored 123.5 points in the ULPBench standard test. TI then announced its SimpleLink C26xx wireless MCU product based on Cortex-M3 and scored 143.6 points.

This week, TI's Cortex M4F-based MSP-432 series successfully surpassed the company's previous record and scored 167.4 points. However, while TI was preparing for the press release, Atmel quickly released a product that scored 185.5 points in the ULPBench test. This is the Cortex M0+-based SAM-L21 MCU product that was announced last year and planned to be released this year. We are very much looking forward to the official announcement of this product's score and its validity.

However, when Ambiq Micro released the scores of its Apollo MCU test, all the above test results were eclipsed. The device based on the Cortex-M4F core is based on subthreshold logic technology and uses logic levels with much smaller voltage fluctuations than traditional CMOS levels. Mike Salas, vice president of marketing at Ambiq, said that this reduction in fluctuation not only speeds up switching transitions compared to traditional fields, but also reduces dynamic power consumption by 1/10.

The low-power leap game looks set to continue for some time. Andreas Eieland, Atmel's MCU commercial product marketing director, told reporters: "Every manufacturer has invested a lot of R&D in the field of low power consumption and is moving forward at a much faster pace than before. I know our current power consumption is the lowest, but you never know where your competitors are going. So, we are also looking for the next step in development."

Levy of the EEMBC consortium said it's tempting to stop hoping for ever-increasing so-called low-energy standards, but developers can get real value from the campaign.

The formulation of standards and the development of small-scale competition can encourage developers to improve their products. Within the specified standards, they will think about how to get better scores and will not take shortcuts. What they have to do is learn how to optimize the code and make low-power devices run faster.

The same lesson applies to hardware design, which is leaning toward offering a wider range of power-saving technologies. Just as software developers are shifting from leaning toward manufacturers to leaning toward consumers. "The same thing is happening with CoreMark," Levy said. "Manufacturers understand that programmers' component choices can improve device performance, and they should have always done so, but now they are incentivizing this behavior through the competition they create."

“One of the things we learned is to increase our flexibility in low-power models a lot,” said Stuart McLaren, product marketing manager at STMicroelectronics. “ULP is just one application for low-power. The others are different, and we need a wide range of models available for developers to choose the right part for their application.”

“We’re also going to have a lot of smarter options for peripherals,” said Alec Bath, applications engineer at STMicroelectronics. “For example, we have address matching in our I2C interface, so the CPU can only be activated if a message is received by the device. Otherwise, it ignores the rules and puts the CPU into sleep mode. We’re also going to have clock sources for ADCs and peripherals that don’t need the CPU clock, so they can kick in when the CPU is slowed down or asleep. We also have DMAs that allow peripherals to transfer data directly to RAM, waking up the CPU only when the transfer is complete.”

Atmel's Eieland cautions that the initial development work on low power consumption is focused on improving the CPU architecture. "But it's not enough to just optimize the CPU," Eieland adds. "We're starting to optimize each peripheral, looking at every transistor in the product. We're developing features that look at clock requirements, the logic that allows a peripheral to operate independently, and the smallest possible board size to do what it needs to do. We're removing timers and even creating multiple power ranges so we can shut down unused circuits and even eliminate their leakage current."

The pursuit of low power consumption provides more opportunities for software. Developers can use software to connect all projects and activate another peripheral device without the CPU being involved.

"Another advantage is that you have to create one IRQ thread for the CPU and one for the peripherals, so hierarchical interrupts can be implemented," Eieland said.

Low-power operation may not affect developers writing their main loops, Eieland added, but they should look for opportunities to improve it using sleep modes and fancy peripherals.

“Today’s programmers don’t care about power consumption, but software plays a critical role in power design, so we spend a lot of time looking for the right software. For example, we took apart a Bluetooth module to see where the components consumed power, and we found that we could save power by reassembling the components correctly,” said Salas of Ambiq.

Meanwhile, there is no doubt that the standard scores will continue to be rewritten. However, everyone agrees that these scores are just a starting point for developers to pursue low power consumption when designing. "The ULP standard is not 100% fair, no standard can be." Eieland also said: "But it does a lot of marketing about low power consumption, and developers can compare and choose the appropriate parts."

Some processors of the EEMBC Association ULPBench, but they can also be used alone.

The power monitoring panel can provide accurate energy consumption indicators for the MCU in working state.

“The individual numbers from the ULP benchmark are a good starting point for estimation,” said STMicroelectronics’ Stuart. “But you need to judge your application. Every low-power application will express itself differently in terms of time spent in sleep mode or speeds at high and low clock speeds. You need to understand your application profile.”

EEMBC's Levy added that developers who focus solely on "winning the highest score" will lose sight of the goal. "There are always trade-offs to be made, so we encourage people to publish their scores regardless of their level." The published final numbers can help developers decide which results are more applicable to their own solutions.

Manufacturers will also help developers improve their design processes to achieve goals that exceed general standards. For example, STMicroelectronics provides developers with the STM32 Cube MX power simulator to estimate the power of the ST MCU used when executing code. Texas Instruments provides its own energy tracking technology EnergyTrace+ to estimate the energy consumption of its MCUs. In addition, the energy monitoring of the EEMBC Association can be used by developers to describe the power usage of their programs, just like implementing the ULPBench power standard.

At the same time, the power standards will continue to develop. According to Levy, "At this stage, the implementation of the standards is concentrated in the CPU and RTC fields. The improvement work we are engaged in will be around more peripheral activities, such as ADC and PWM fields." The standards will be implemented in two parts, and TI Chairman Stefan Schauer also welcomed additional participants. Interested teams can click on the original text below to obtain the email address for more details.