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Since both devices already have a built-in Wi-Fi chip, can they skip the router and "talk through the air" directly when sending lightweight commands?

If you are using or evaluating Realtek Ameba Wi-Fi SoCs, don't overlook a practical feature that already ships in the SDK: the Ameba Wi-Fi CAST solution.

01. What Is Wi-Fi CAST? No Connection Setup, Direct Sending at the Data Link Layer

Traditional Wi-Fi communication works like a "phone call": a device must first scan for a network, handshake and associate, and obtain an IP address. Only after a standard Wi-Fi connection is established can data be transferred.

Wi-Fi CAST, by contrast, is a connectionless Wi-Fi communication protocol defined by Realtek. It works more like a "walkie-talkie":

Devices do not need to establish a traditional Wi-Fi connection, and data does not have to be encapsulated layer by layer through the TCP/IP stack. Application data is passed straight to the Wi-Fi driver, and sending and receiving are completed directly at the data link layer (MAC layer).

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This "shortcut" design directly solves two engineering pain points:

Fast networking and low-latency response: Commands are sent and received immediately. Skipping the Wi-Fi connection setup reduces latency.
Microamp-level ultra-low power: Because no regular Wi-Fi connection state has to be maintained, a transmitter with nothing to send can enter a low-power sleep mode, which greatly extends the battery life of battery-powered products.

Many engineers have used similar connectionless protocols, and their biggest concern is often: "It just sends blindly. What if packets are lost?"

On this point, Wi-Fi CAST provides industrial-grade reliability in its protocol design:

It supports ACK responses, timeout retransmission, and packet sequence-number deduplication. For commands that need confirmation, you can enable acknowledgment and retransmission; for periodically reported data, you can leave them off. The retransmission count and timeout are configured by the developer to suit the scenario.

02. How Flexible Is the Topology?

In real product design, simple point-to-point communication is often not enough. Wi-Fi CAST gives developers great freedom in network topology:

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Without any router involved, Wi-Fi CAST natively supports one-to-one, one-to-many, and many-to-many device connections and communication. Whether it is single-point control or a main control panel broadcasting commands to many terminals at once, multi-terminal coordination is easy to achieve and scales well. Broadcast requires no pairing and the data is not encrypted; unicast requires pairing first and can enable encryption.

Hybrid networking: stay online and stay direct, at the same time. Many engineers ask: "With Wi-Fi CAST enabled, can the device still connect to the home router and access the Internet as usual?"

Absolutely! While a device keeps a standard Wi-Fi connection to the router (sending and receiving cloud data as normal), it can still use Wi-Fi CAST concurrently to communicate directly with other nearby nodes, forming a flexible hybrid network.

03. Four Official Reference Examples: What Else Can You Build Besides a Remote Control?

The Realtek SDK includes four reference examples: Control, Security (encryption), UART (serial transmission), and OTA (over-the-air upgrade). Building on these capabilities, developers can extend to the following practical scenarios:

Use Case 1: Wireless Switch & Long-Range Remote Control (based on the Control example)

Whether you are building a toy or model-aircraft remote, synchronized multi-node lighting control, or a smart-home combination such as a "wireless bedside switch + ceiling light", Wi-Fi CAST delivers a press-and-respond experience.

Compared with a traditional BLE remote, it offers a longer range, and with hybrid networking it delivers a highly reliable experience where "local group control still responds even when the Internet is down". You can even build custom Wi-Fi Mesh-style applications.

Use Case 2: Wireless UART Pass-Through Without Physical Cabling (based on the UART example)

Many split-type devices, sensors, and industrial modules exchange data over a UART serial link, which usually requires running a physical cable. When the devices are far apart or wiring is inconvenient, installation becomes very troublesome.

With the Wi-Fi CAST UART example, data entered on the serial port at one end is sent by wireless broadcast to the other end and output on that end's log port. (If data confidentiality matters, you can also use the Security example for encrypted transmission.)

As a starting point, this can serve as a wireless alternative to a traditional wired serial link, and you can build on it to develop router-free "wireless UART pass-through" applications.

Use Case 3: On-Site Batch Wireless Upgrade for Offline Devices (based on the OTA example)

When many devices are installed outdoors, in a factory, or in a newly renovated home with no Wi-Fi router coverage, how do you update their firmware?

With the Wi-Fi CAST OTA example, a technician can use one main device (which must first obtain the firmware) to push the firmware package to the surrounding devices over the data link layer, completing a local firmware upgrade quickly!

Use Case 4: Low-Cost Wireless Voice Intercom and Multimedia Collaboration

Many enthusiasts like to stream audio over a connectionless Wi-Fi protocol to build a "digital walkie-talkie", but they are often limited by MCUs that lack audio peripherals and have to add complex op-amp and codec circuits externally.

In the Ameba family that supports Wi-Fi CAST, the RTL8726E / RTL8713E have a high-performance DSP and an Audio ADC/DAC built in! These on-chip resources provide a foundation for voice capture, processing, and playback, and you can go on to explore applications such as "voice capture → noise reduction → wireless transmission → audio playback".

04. A Minimal Development Experience

To help developers get started as fast as possible, the Ameba SDK leaves low-level details such as frame encapsulation to the driver, and exposes a very clean C interface.

To get two Ameba development boards communicating, there are only 4 core steps:

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We recommend running the UART example first: enter data on the serial port of one board and check the log port of the other. If the data arrives, both boards are on the same channel and sending and receiving work correctly. For interface details and complete examples, see the Wi-Fi CAST Development Guide.

05. Getting Development Resources

The Wi-Fi CAST protocol now covers the entire Realtek Ameba SoC series. Whether your project values cost-effectiveness, ultra-low power, or multimedia compute, you can find a matching model.

👇 Try it yourself

Reading only gets you so far, so flash a board and see it run!

Click the link to go straight to the Realtek official developer documentation center and read the full Wi-Fi CAST Development Guide.

If you need technical support for project selection or solution evaluation, feel free to contact us. Our engineering team is ready to talk with you!