NXP has developed a smart-meter chip based around ARM's Cortex-M0, which is available to run wireless protocol stacks.
Called EM773, the chip includes a 'metrology engine' that takes care of single phase voltage and current measurement, and calculates reactive power, apparent power, power factor ratio, and total harmonic distortion (THD).
"It is not aimed at the traditional smart meter market," Rolf Hertel, director of smart metering at NXP told Electronics Weekly. "It has been made available for non-billing applications. So: plug meters for measuring an individual appliance or measuring energy consumption in white goods, where it an communicate wirelessly to an in-home energy control unit or an expanded in-home energy display."
The firm also predicts industrial applications.
Hertel would not reveal what is inside the metrology unit, saying that is it aimed at non-expert designers who are expected to use the application circuits provided.
"This is a new market segment, and it is particularly for customers that do not have in-depth knowledge of circuits," he said. "The customer should not care how the metrology works."
NXP promotional literature declares 1% accuracy, which Hertel insists is correct.
However, even with the firm's simplest proposed current interface circuit - which uses 1% resistors - accuracy is defined by NXP as "0.1W to 250W total range", which suggests 0.04% resolution and possibly 0.04% accuracy with the right resistors.
A more complex dual ranging current circuit will deliver "1% accuracy for 1-400W (0.01W to 400W total range)" - possible 0.0025% resolution.
The ARM microcontroller has been sized to run wireless communications in order to transmit measurement data to, and receive commands from, a home energy control unit, or other data concentrator or controller.
"Complete wireless M-Bus protocol will run on the Cortex-M0 at 48MHz, with lots of performance left over for customer applications," said Hertel.
Up to 32kbyte of flash and 8kbyte RAM is available.
For wired applications, built-in SPI, I2C serial bus are included, as is a UART which can be used for RS485 or IrDA infra-red.
For wireless use, one of the firms OL23xx transceiver chips is required alongside the EM773.
The firm is selling a functioning plug meter (pictured) as a demonstration kit. 
For $250, the plug includes built-in wireless M-Bus plus a partner RF dongle - based around the firm's OL2381 wireless transceiver and LPC1343 microcontroller - for the host computer. 
Although full circuit diagrams and PCB layouts can be downloaded, Hertel said: "This is not a reference design. It is not guaranteed to meet EMC. Customers are free to use it, as long as they do not make us liable for compliance."
This version of the plug meter demo kit disappointingly uses an inefficient RC dropper as a mains power supply, rather than an efficient switching design - at least three other chip makers have PSU switching chips with losses as low as 20mW.
A later version of the circuit, said Hertel, uses NXP's TEA1520T switching PSU chip (dissipating 100mW minimum), cutting the power consumption of demo plug meter to 400mW.