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Tiny $2 IoT module runs FreeRTOS on Realtek Ameba WiFi SoC

Sep 14, 2016 — by Eric Brown — 3,113 views

[Updated: Sept. 15] — Pine64’s $2 “PADI IoT Stamp” module is based on Realtek’s new “RTL8710AF” Cortex-M3 WiFi SoC, a cheaper FreeRTOS-ready competitor to the ESP8266.

Realtek’s RTL8710AF WiFi system-on-chip began showing up on tiny “B&T” labeled modules in July in China on AliExpress, as described in this Hackaday post. The RTL8710AF SoC offers an even lower cost, and almost identical alternative to Espressif’s Tensilica L106-based ESP8266 WiFi SoC. The SoC costs a bit over $3 individually, but can be had for as little as $1.99 in volume.

Now, Pine64, the maker of the popular Pine-A64 Linux hacker board, has created a tiny PADI IoT Stamp module using the RTL8710AF, and plans to sell it for the same $1.99 price as the SoC alone, in quantity.

Pine64’s PADI IoT Stamp compared to… a postage stamp
(click image to enlarge)

Pine64’s 24 x 16 x 3mm PADI IoT Stamp builds upon the 83MHz RTL8710AF with a WLAN MAC and baseband, RF balun, PA, LNA receiver, SAW filter, and power management. The SoC also integrates 1MB of on-chip ROM, in addition to 512KB of SRAM and 1MB of SPI flash.

PADI IoT Stamp block diagram
(click image to enlarge)

The RTL8710AF’s internal WiFi radio supports 2.4GHz 802.11b/g/n communications. The SoC also provides a generous set of I/O interfaces, including SPI at up to 41.4Mbps, along with up to 3x I2C, 4x PWM, PCM, 3x UART, and 17x GPIO signals.

PADI IoT Stamp pinout
(click image to enlarge)

The PADI IoT Stamp’s design incorporates a 3dBi PCB antenna. It’s powered by 3.0V to 3.6V DC, and can operate over a wide temperature range of -20 to 85℃. The module currently ships with FreeRTOS, and Mbed is being developed.

Realtek RTL8710 background

Although we were unable to locate it on Realtek’s website at press time, the RTL8710 SoC appears to be a recent, low-end addition to the “Ameba WiFi SoC” family that debuted at CES 2015.

Realtek Ameba SoC family promotional graphic from CES 2015
(click image to enlarge)

The table below, obtained from a Realtek slide deck, compares a few key specs of the three earlier Ameba WiFi SoCs: the RTL8711AF, RTL8711AM, and RTL8195AM. The differences among them are in package size, and in their on-chip RAM and flash; but all three can have their Cortex-M3 cores clocked at up to 166MHz.

Realtek Ameba SoC family specs comparison, not including the RTL8710
(click image to enlarge)

The RTL810AF appears to offer comparable ROM, RAM, and flash memories, but only half the clock rate of the other parts, at 83MHz. According to a more extensive comparison table in this CNXSoft post, the RTL8711AM model adds 1x ADC interface, while the RTL8195AM adds Ethernet, USB host and device, SDIO master and slave, and both ADC and DAC interfaces to the I/O mix. The CNXSoft post’s table also differs slightly from the table we obtained from Realtek’s slide deck, with regard to memories in the RTL8195AM and RTL8711AM.

Like Espressif’s popular ESP8266, the Realtek RTL8710 SoC can act as either a standalone system running the open source FreeRTOS, or as a slave device to other — often Arduino based — computers.

Other RTL810AF modules

We were alerted to Pine64’s PADI IoT Stamp by a post at CNXSoft, which also recently posted a hands-on review of a similarly RTL8710AF-based module from ICStation, called the B&T RTL-00. That one sells for $2.85 in volume.

There’s also an 83MHz, 22.5 x 13mm, RTL8710AF-based F10AFIM13-B1 module from Shenzhen Ofeixin Technology. The F10AFIM13-B1’s photo (below), which is absent the usual shield for the RTL8710 SoC and other topside components, offers a glimpse at what goes into one of these tiny modules, beyond the Realtek WiFI SoC core.

Ofeixin’s RTL8710-based F10AFIM13-B1 module
(click image to enlarge)

Additionally, a larger RTL8710-based board is documented at Realtek’s Ameba IoT portal site. The Ameba RTL8710 Board (below-left) appears to be Realtek’s official hardware/software development platform for its RTL8710 SoC.

Ameba RTL8710 (left) and RTL8195 development boards
(click images to enlarge)

An Ameba RTL8195 Board (above-right), also listed at the Ameba IoT portal site, serves as the official development platform for the RTL8195 SoC, and adds an Arduino expansion interface. Both boards share an Ameba software development kit that includes FreeRTOS support, as well as support for using the Arduino IDE in hybrid designs.

Realtek’s “Standard SDK of Ameba” software stack
(click image to enlarge)

“The Standard SDK of Ameba offers cloud integration, full-fledged internet-of-things protocol support and maximized coding flexibility,” states the SDK page.

Further information

The PADI IoT Stamp will soon go on sale for $1.99 in quantity. More information may be found on the Pine64 PADI IoT Stamp product page.

— with additional reporting by Rick Lehrbaum

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