Sona IF573: Virtual Simultaneous Dual Band (VSDB) for AP/STA Mode on Separate Frequencies

  1. Introduction
  2. Technical Considerations for AP/STA Mode
    1. Frequency Band Recommendations
    2. Dynamic Frequency Selection (DFS) and Channel Limitations
    3. 6 GHz Band Support
    4. Performance and Power Usage Impact
  3. Requirements
  4. Hardware Setup and Initial Programming
    1. Physical Assembly and Console Connection
    2. Programming the image to eMMC
    3. Basic Configuration (Network Manager)
    4. Advanced Configuration (hostapd and sdcsupp)
    5. IP Routing and Network Address Translation (NAT)
  5. Conclusion and Next Steps
    1. Key Achievements
    2. Final Verification
    3. Troubleshooting Tip
Sona IF573

Introduction

This document provides a tutorial on configuring the Sona IF573 wireless module to operate simultaneously in both Access Point (AP) mode and Client (Station, STA) mode across different Wi-Fi frequencies.

This guide is specifically tailored for the following hardware configuration:

The guide will first demonstrate how to use the nmcli (NetworkManager Command Line Interface) utility for initial setup of both the AP and STA interfaces. Following this, we will explore advanced configuration for the AP using the hostapd utility and a separate configuration file for the STA interface controlled by sdcsupp, Ezurio’s fork of the wpa_supplicant.

The Sona IF573 utilizes a feature known as Virtual Simultaneous Dual Band (VSDB). This capability allows the device to function as an AP on one frequency band (e.g., 2.4 GHz) and as an STA on a different frequency band (e.g., 5 GHz) by rapidly time-sharing the single radio.

Technical Considerations for AP/STA Mode

Frequency Band Recommendations

  • AP Mode: It is generally recommended to configure the AP on the 2.4 GHz band.
  • STA Mode: It is generally recommended to configure the STA on the 5 GHz or 6 GHz bands.

Dynamic Frequency Selection (DFS) and Channel Limitations

The use of the 5 GHz band for AP mode introduces a significant regulatory constraint known as Dynamic Frequency Selection (DFS).

  • DFS requires the radio to constantly listen for and avoid interference with radar signals.
  • The Sona IF573 is not capable of detecting RADAR signals.
  • Depending on your geographic regulatory domain, this limitation will significantly restrict the available channels for AP operation in the 5 GHz band.
  • STA mode does not have this same RADAR detection requirement, meaning you have a greater range of channels available for association.

6 GHz Band Support

  • The Sona IF573 does not support AP mode in the 6 GHz band.
  • STA mode can utilize the 6 GHz band, provided the module is configured with a regulatory domain that supports it.

Performance and Power Usage Impact

Running the radio in simultaneous AP/STA (VSDB) mode will negatively affect both power consumption and network throughput.

  • This is due to the radio constantly switching between the configured frequencies to transmit and receive packets.
  • For designs where battery life or throughput are critical requirements, it is strongly recommended to operate the radio in AP/STA mode on the same Wi-Fi channel and frequency band, if feasible.

Requirements

To follow this application note, the following hardware and software components are required:

Hardware Setup and Initial Programming

This section details the physical assembly of the components and the process for flashing the operating system image to the eMMC storage on the SOM.

Physical Assembly and Console Connection

SOM Insertion

Insert the Nitrogen8M Plus SOM into the designated SMARC port on the SMARC Carrier Board and secure it in place with screws.

Antenna Attachment

Attach two of the included FlexPIFA antennas to the radio ports on the SOM as shown. The third antenna port is for Bluetooth, which we will not be using in this tutorial, so you can leave it disconnected.

image-20251120-165011.png

Note: For best performance, it is recommended to attach the antennas to polycarbonate and place them orthogonally (at right angles) as shown.

Console Setup

Connect the specialized cable (provided with the kit) to the SERIAL connector on the SMARC Carrier Board.

The other end of this cable features two DB9 connectors. Connect your USB-to-DB9 adapter to the connector labeled CONSOLE.

Start your preferred terminal software (e.g., minicom or TeraTerm) on the host machine.

Configure the terminal port settings to: 115200 Baud, No Parity (N), 8 Data Bits, 1 Stop Bit (115200/N/8/1).

image-20251120-165318.png

Programming the image to eMMC

There are several methods for programming the eMMC. For this guide, we will use the highly reliable U-Boot USB Mass Storage (UMS) Gadget Method. (For information on other methods, please consult the document: Programming eMMC on Ezurio System-On-Modules).

Connect USB

Plug a USB-C cable from your host machine into the USB-C port on the SMARC Carrier Board.

image-20251120-165637.png

Access U-Boot

  • Power up the carrier board by plugging in the power adapter.
  • In your terminal software, immediately press any character (e.g., Space or Enter) to stop the auto-boot process and access the U-Boot prompt(=>).
  • Enable UMS Gadget: Enable the UMS Gadget for the eMMC. The primary eMMC device is typically mmc 0.

    • At the U-Boot prompt, enter the following command:

      => ums 0 mmc 0:0
image-20251119-194904.png

Flash the Image

At this stage, your host machine should recognize the SOM's eMMC as a new USB drive/device.

  • It is recommended to use dd from a Linux terminal or balenaEtcher for a graphical experience to flash the image file.
    • The is an example using balenaEtcher.
  • image-20251119-202042.png

    Finalize: Once the flashing process is complete, you can safely remove the power and the USB-C cable. The board is now ready to boot the new image.

Basic Configuration (Network Manager)

Booting the device

  • Once you have flashed the image and unplugged the USB-C and power cables with the Console cable connected to the DB9 cable and your terminal emulation program running, connect the power. The SOM boots.
  • Once you see the login: prompt, enter root and press enter.

  • To confirm that the radio is loaded correctly, you can enter ip -a. You should see an entry for wlan:0

    image-20251119-204932.png

Disabling Hostapd to Prevent Conflicts

Before configuring the wireless interfaces using nmcli, you must ensure that the hostapd service, which might be configured to start automatically by the default image, is stopped and disabled.

CommandPurpose
systemctl stop hostapdImmediately terminates any running instance of the service.
systemctl status hostapdCheck Status (Optional): Verifies the service is stopped.
systemctl disable hostapdRemoves the system boot links, ensuring hostapd does not restart on subsequent reboots.

Expected Status Output

When you run systemctl status hostapd, the expected output should show the service state as inactive or dead.If the hostapd package was not pre-installed or is named something else, you might see the message "Unit hostapd.service could not be found." This is also acceptable, as it confirms the service is not active and cannot cause a conflict.

Ensure NetworkManager is Running

Before running nmcli commands, confirm that the NetworkManager service is running. If it is disabled or stopped, your configuration commands will fail.
Check Status
Use systemctl status to check the service status.
systemctl status NetworkManager
Start/Enable (If needed)

If the status shows "inactive" or "disabled," use the following commands:

systemctl enable NetworkManager
systemctl start NetworkManager

Note: Enabling the service ensures NetworkManager will start automatically on future reboots.

nmcli Configuration Steps

The Virtual Simultaneous Dual Band (VSDB) feature requires creating a second virtual interface (wlan1) linked to the physical device (wlan0) to operate in AP mode.
Create the Virtual AP Interface (wlan1)
Use the iw command to create the virtual interface that will be dedicated to Access Point mode. 
iw dev wlan0 interface add wlan1 type __ap
Make the Virtual Interface Permanent
By default, the virtual interface (wlan1) created via the iw command is removed when the device reboots. To ensure wlan1 is created automatically on every boot, we will create a systemd service.
Create the systemd Service File
Use vi to create the service file:
vi /etc/systemd/system/create-wlan1.service

Enter the following content into the file:

[Unit]
Description=Create Virtual AP Interface for VSDB
Documentation=man:iw(8)
After=sys-subsystem-net-devices-wlan0.device
BindsTo=sys-subsystem-net-devices-wlan0.device

[Service]
Type=oneshot     
RemainAfterExit=yes
ExecStart=/usr/sbin/iw dev wlan0 interface add wlan1 type __ap
User=root
Group=root
StandardOutput=journal
StandardError=journal

[Install]
WantedBy=multi-user.target
Enable and Start the Service
systemctl daemon-reload
systemctl enable create-wlan1.service
systemctl start create-wlan1.service

Note: The name of the service file must match the name you use in the systemctl commands.

Configure and Activate the AP Network (wlan1)

Create Basic AP
nmcli con add con-name aptest ifname wlan1 type wifi ssid aptest autoconnect yes 802-11-wireless.mode ap ipv4.method manual ipv4.addresses 192.168.42.1/24
Configure WPA3 security

Modify the connection to set the frequency band, channel, and WPA3-SAE security.

nmcli con modify aptest wifi.band bg wifi.channel 6 wifi-sec.key-mgmt sae wifi-sec.psk "myappsk1"
Activate the connection
nmcli con up aptest

Configure and Activate the Client Network (wlan0)

Create a NetworkManager connection profile named home on the primary interface wlan0. This connection will associate with your existing Wi-Fi network (e.g., on the 5 GHz band).
nmcli con add con-name home ifname wlan0 type wifi ssid FAE-6g 802-11-wireless-security.key-mgmt sae 802-11-wireless-security.psk "mypresharedkey"
Activate the connection
nmcli con up home

Completing the Network Setup

The configuration steps above successfully create and activate both the Access Point (wlan1) and Client (wlan0) interfaces. However, clients connected to the AP will not have internet access until the routing path is defined.To enable client devices connected to theaptestnetwork to reach the external network viawlan0, proceed to the "IP Routing and Network Address Translation (NAT)" section.

Advanced Configuration (hostapd and sdcsupp)

To use the advanced configuration files, we must first disable NetworkManager and enable the core wireless utilities (hostapd and wpa_supplicant) for interface control.

Disable NetworkManager and Enable Hostapd

Since the previous section used nmcli (which controls NetworkManager), we need to disable the service responsible for it and enable the services we plan to use.
CommandPurpose
systemctl stop NetworkManagerImmediately stops the running NetworkManager service.
systemctl disable NetworkManagerPrevents NetworkManager from starting automatically on future reboots.
systemctl enable hostapdEnables the hostapd service, ensuring it starts automatically on future reboots for AP functionality.
systemctl enable wpa_supplicantEnsures wpa_supplicant starts automatically on future reboots for STA functionality.

Create the Virtual Interface

You must first create the virtual AP interface (wlan1). If you did this in the nmcli section, you can skip this step.To confirm that you do not need to create a wlan1 interface, enter ip a at the command prompt. If you see a wlan0 and a wlan1 interface you can go on to the next step, if not, use the iw command to create the virtual interface that will be dedicated to Access Point mode:
iw dev wlan0 interface add wlan1 type __ap

Configure the Access Point (AP) using hostapd

Backup Existing Configuration

It is best practice to back up the default configuration file before creating a new one.

mv /etc/hostapd.conf /etc/hostapd.conf.orig
We will create a configuration file for hostapd to manage the virtual AP interface (wlan1) on the 2.4 GHz band with mixed-mode WPA2/WPA3 security.
Create the Hostapd Configuration File
Use vi (or your preferred editor) to create the file /etc/hostapd.conf:
vi /etc/hostapd.conf
Enter Configuration Details

Enter the following configuration. This sets up a basic 2.4 GHz AP with WPA2-PSK security.

ctrl_interface=/var/run/hostapd
interface=wlan1
driver=nl80211
ssid=SonaAP_Hostapd
channel=6
hw_mode=g
wmm_enabled=1

# WPA2 Security
wpa=2
rsn_pairwise=CCMP
ieee80211w=2
wpa_key_mgmt=WPA-PSK
Edit the Hostapd Service File for Stability
You must add dependencies to the hostapd.service file to prevent startup failure due to race conditions at boot.
  • Use vi to edit the service file (location may vary, commonly found here):
    vi /usr/lib/systemd/system/hostapd.service
  • Locate the [Unit] section and add the following two lines to ensure the service waits for the physical interface (wlan0) to be fully initialized by the kernel:
    [Unit]
Description=Hostapd IEEE 802.11 AP, IEEE 802.1X/WPA/WPA2/EAP/RADIUS Authenticator
After=sys-subsystem-net-devices-wlan0.device
Requires=sys-subsystem-net-devices-wlan0.device
# ... rest of file ...
Reload and Restart Hostapd

After saving the change, reload the systemd configuration to recognize the new dependencies and restart the service:

systemctl daemon-reload
systemctl enable hostapd
systemctl restart hostapd

Configure the Client (STA) using sdcsupp

The client interface (wlan0) will be controlled directly by Ezurio’s fork of the wpa_supplicant called sdcsupp to associate with the external Wi-Fi network.
Disable the default service

Create a configuration file specific to the SSID inside the recommended directory.

systemctl stop sdcsupp
systemctl disable sdcsupp
Create the sdcsupp Configuration File

Create a configuration file specific to the SSID inside the recommended directory.

mkdir -p /etc/wpa_supplicant
vi /etc/wpa_supplicant/FAE-6g.conf
Enter Network Details

Enter the configuration for your target network using WPA3 (SAE) security.

ctrl_interface=/var/run/sdcsupp
ctrl_interface_group=0
update_config=1

network={
    ssid="FAE-6g"
    psk="yourpresharedkeyhere"
    key_mgmt=SAE
    ieee80211w=2
    }
Create the Custom Service File 
vi /etc/systemd/system/sdcsupp-client.service
Enter the Custom Service Content
[Unit]
Description=Ezurio SDC Supplicant Client for wlan0
Requires=sys-subsystem-net-devices-wlan0.device
After=sys-subsystem-net-devices-wlan0.device

[Service]
Type=simple
ExecStart=/usr/sbin/sdcsupp -i wlan0 -c /etc/wpa_supplicant/FAE-6g.conf
Restart=on-failure

[Install]
WantedBy=multi-user.target
Enable and Start the New Service
systemctl daemon-reload
systemctl enable sdcsupp-client.service
systemctl start sdcsupp-client.service

IP Routing and Network Address Translation (NAT)

The goal of this section is to turn the Sona IF573 into a router: clients connect to the AP interface (wlan1), and traffic is forwarded to the external network via the associated STA interface (wlan0).

Assign a Static IP to the AP Interface

Set Static IP Persistence

Create a service to ensure the static IP remains across reboots, as NetworkManager is disabled.

vi /etc/systemd/system/set-ap-static-ip.service
Enter the following content
[Unit]
Description=Set static IP for AP interface wlan1
After=sys-subsystem-net-devices-wlan1.device
Requires=sys-subsystem-net-devices-wlan1.device

[Service]
Type=oneshot
RemainAfterExit=yes
ExecStart=/sbin/ip addr add 192.168.42.1/24 dev wlan1

[Install]
WantedBy=multi-user.target
Enable and start the service
systemctl daemon-reload
systemctl enable set-ap-static-ip.service
systemctl start set-ap-static-ip.service
Bring the Interface Up
ip link set dev wlan1 up

Configure dnsmasq for the AP Network

Create a minimal configuration file for dnsmasq to serve IPs on the wlan1 interface.
Disable the Default Service
systemctl stop dnsmasq
systemctl disable dnsmasq
Create the dnsmasq-custom.service file
vi /etc/systemd/system/dnsmasq-custom.service
Content
[Unit]
Description=DNS forwarder and DHCP server (Custom)
After=network.target

[Service]
Type=simple
ExecStart=/usr/bin/dnsmasq -C /etc/dnsmasq.conf --keep-in-foreground
Restart=on-failure

[Install]
WantedBy=multi-user.target
Update /etc/dnsmasq.conf
vi /etc/dnsmasq.conf
Content
interface=wlan1
dhcp-range=192.168.42.10,192.168.42.250,12h
dhcp-option=3,192.168.42.1
dhcp-option=6,192.168.42.1
no-resolv
Start the Custom dnsmasq Service
systemctl daemon-reload
systemctl enable dnsmasq-custom.service
systemctl start dnsmasq-custom.service

Enable IP Forwarding

The Linux kernel must be instructed to forward packets between interfaces, which is the core function of a router.

Enable Forwarding Temporarily

Enable IP forwarding immediately for the current session.

echo 1 > /proc/sys/net/ipv4/ip_forward
Enable Forwarding Permanently

Edit the system configuration file to ensure IP forwarding remains active after a reboot.

vi /etc/sysctl.conf
Uncomment or add the following line
net.ipv4.ip_forward = 1
Apply the permanent change without rebooting
sysctl -p

Configure Network Address Translation (NAT)

NAT is essential to translate the private IP addresses of clients connected to wlan1 into the single public IP address assigned to the wlan0 interface by the upstream router. This allows the outgoing traffic to be correctly routed over the internet.
Apply the NAT Rule
Use iptables to set up the MASQUERADE rule. This rule takes all traffic originating from the local AP network (192.168.42.0/24) and sends it out through the STA interface (wlan0), dynamically replacing the source IP address with wlan0's external IP.
iptables -t nat -A POSTROUTING -o wlan0 -j MASQUERADE
Explanation
  • -t nat: Specifies the Network Address Translation table.
  • -A POSTROUTING: Appends the rule to the chain executed just before the packet leaves the system.
  • -o wlan0: Specifies the outgoing interface (your client interface).
  • -j MASQUERADE: The jump target that performs dynamic NAT
Save the iptables Rules
By default, iptables rules are lost upon reboot. You must use a utility like iptables-save to persist them.
iptables-save > /etc/iptables/rules.v4
Set NAT Persistence

Create a service to restore the NAT rules on boot.

vi /etc/systemd/system/netfilter-persistent.service
Content
[Unit]
Description=Netfilter Persistent Rules
After=network.target

[Service]
Type=oneshot
ExecStart=/sbin/iptables-restore /etc/iptables/rules.v4
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target
Enable and start the service
systemctl daemon-reload
systemctl enable netfilter-persistent.service
systemctl start netfilter-persistent.service

Conclusion and Next Steps

You have successfully configured the Sona IF573 module to operate in Virtual Simultaneous Dual Band (VSDB) mode, establishing a persistent Access Point (AP) and a functional Client (STA) connection. This setup utilizes dedicated system services (hostapd, sdcsupp, dnsmasq-custom) and persistent kernel settings (iptables, sysctl) to ensure stability across reboots.

Key Achievements

Service Stability

The system is configured to run the AP, STA, and DHCP services reliably using custom systemd unit files, avoiding common conflicts and race conditions.

Persistent Networking

The static IP address and the critical NAT/IP forwarding rules are applied automatically at boot time, ensuring the network is operational without manual intervention.

Functional Gateway

The device successfully operates as a network gateway, routing traffic from the local AP network (wlan1) out through the client connection (wlan0).

Final Verification

To confirm the entire setup is robust, perform a full end-to-end test:

Reboot the System

Perform a final system reboot to verify all services (hostapd, sdcsupp-client, dnsmasq-custom) start correctly.

Verify IP

After logging in, confirm the static IP is correctly set: ip a show wlan1 should show inet 192.168.42.1/24.

Client Connectivity

Connect a laptop or smartphone to the SonaAP_Hostapd network and verify it receives a 192.168.42.x IP address and can successfully browse the internet.

Troubleshooting Tip

If the external connection fails, always verify the NAT rule is loaded: iptables -t nat -L POSTROUTING -v. If the rule is missing, ensure the netfilter-persistent.service is enabled and active