Atmel's Sleepwalking MCUSeptember 24, 2012
Author: Tom R. Halfhill
Atmel today announced a new 32-bit microcontroller that it claims is the world’s most power-efficient Cortex-M4 MCU. At its top speed of 48MHz, the SAM4L’s typical power consumption is as low as 17.3mW. But at 12MHz, it uses only 2.16mW while fully active and remains surprisingly functional even while sleeping. Chips are sampling now, and production quantities are coming in November.
The SAM4L cuts power consumption by supporting a wide voltage range, by using voltage/frequency scaling, and by spending most of its time sleeping. Atmel has achieved this flexibility despite fabricating the chip in a 130nm CMOS process that is one or two nodes behind competing microcontrollers.
Perhaps most important is the SAM4L’s ability to sleep—and to sleepwalk. The key to prolonging battery life is to sleep as much as possible, then quickly wake up and do a brief burst of work before slumbering again. In deep sleep, only the real-time clock (RTC) remains awake. It can supervise simple tasks without disturbing the CPU, because the peripherals have some autonomy.
For example, without CPU intervention, the chip can respond in only two clock cycles to many types of I/O events. Using an internal DMA engine, peripherals can exchange data and even perform analog-to-digital and digital-to-analog conversions using the on-chip ADC and DAC. Programmers can define conditions—such as ADC thresholds—that will trigger an event to which a peripheral responds.
Although MCUs based on the ARM Cortex-M0+ consume even less power, they lack the Cortex-M4’s DSP extensions, such as a single-cycle multiply-accumulate instruction. Also, their stripped-down Thumb-2 CPUs aren’t compatible with 32-bit ARM code. The SAM4L is a strong addition to Atmel’s product line, which is dominated by MCUs based on Atmel’s proprietary CPU cores instead of the industry-standard ARM architecture. Atmel’s pricing is competitive, too: $3.90 to $4.12 in 1,000-unit volumes.