Wireless Serial Port #

This application uses two Gecko OS devices each running Gecko OS to demonstrate how to create a wireless serial port. A character typed into the serial port of Module 1 appears instantly at the output of the Module 2 serial port (and vice versa).

Features demonstrated #

• Serial Interface Stream Mode
• Use of the wlan and softap wireless interfaces
• TCP client and TCP server
• UDP client and UDP server

Module 1 is configured to start the softap interface and a server on bootup.

Module 2 is configured to use the wlan interface and connect a client to the Module 1 softap server.

The final configuration step places both modules into serial interface stream Mode.

The client/server configuration can use either TCP or UDP protocols.

Wireless Serial Port using TCP #

We start by configuring each of the modules, one as a TCP server and one as a TCP client.

Copy and paste the commands in the left hand column of the following table into a Gecko OS terminal connected to Module 1.

Module 1 TCP Server Configuration Settings #

set softap.auto_start               true
set softap.dhcp_server.enabled      on
set softap.ssid                     server_ap
set softap.dns_server.url "Gecko OS.com"

set tcp.server.auto_interface       softap
set tcp.server.auto_start           true
set tcp.server.port                 3000
set tcp.server.idle_timeout         300
set tcp.server.connected_gpio       5

set tcp.keepalive.enabled           1
set tcp.keepalive.initial_timeout   10

set bus.mode                        stream

save
reboot

<- softap auto starts on reboot
<- DHCP server is enabled
<- Set server softap name
<- Set server DNS name

<- TCP server uses softAP interface
<- TCP server auto starts on reboot
<- TCP server port
<- Don't disconnect clients too quickly
<- GPIO indicates client connection

<- Check the TCP connection is still alive
<- Initial TCP check timeout is 10s

<- Use serial bus stream mode

<- Save settings to flash
<- Reboot the module

On rebooting, Module 1 automatically starts the softap, starts the TCP server, waits for a connection on port 3000 and enters stream mode. Data sent to the Module 1 UART is transmitted over the softap interface.

Now, copy and paste the commands in the left hand column of the following table into a Gecko OS terminal connected to Module 2.

Module 2 TCP Client Configuration Settings #

set wlan.ssid                        server_ap
set wlan.auto_join.enabled           true

set tcp.client.remote_host "Gecko OS.com"
set tcp.client.remote_port           3000
set tcp.client.auto_interface        wlan
set tcp.client.auto_retries             0
set tcp.client.auto_start               1

set tcp.keepalive.enabled               1
set tcp.keepalive.initial_timeout      10

set bus.mode                       stream

save
reboot

<- Set name of Wi-Fi AP to join
<- Turn on wlan auto-join

<- Set host for tcp client auto-connect
<- Set port for tcp client auto-connect
<- Set interface for tcp client auto-connect
<- No auto retries, TCP keepalive checks the connection
<- Enable tcp client auto-connect

<- Check the TCP connection is still alive
<- Initial TCP check timeout is 10s

<- Use serial bus stream mode

<- Save settings to flash
<- Reboot the module

On rebooting, Module 2 automatically connects to the wlan, connects as a client to the TCP server running on Module 1 and enters stream mode. Data sent to the Module 2 UART is transmitted over the wlan interface.

TCP Wireless Magic! #

At this point, all characters typed into the Module 1 serial port appear immediately on the Module 2 serial port output (and vice versa). Give it a go, it's like a little piece of wireless magic!

Wireless Serial Port using UDP Client/Server Configuration #

The UDP client/server configuration is similar to the TCP configuration, with changes due to the different options available for UDP. We start by configuring each of the modules, one as a UDP server and one as a UDP client.

Copy and paste the commands in the left hand column of the following table into a Gecko OS terminal connected to Module 1.

Module 1 UDP Server Configuration Settings #

set softap.auto_start           1
set softap.dhcp_server.enabled  1
set softap.ssid                 test1ssid
set softap.passkey              test1secretkey

set udp.server.auto_interface   softap
set udp.server.auto_start       1
set udp.server.port             8000
set udp.server.lock_client      1

set bus.mode                    stream

save
reboot

<- softap auto starts on reboot
<- DHCP server is enabled
<- Set server softap name
<- Set server softap passkey

<- UDP server uses softAP interface
<- UDP server auto starts on reboot
<- UDP server port
<- No client after the first is allowed

<- Use serial bus stream mode

<- Save settings to flash
<- Reboot the module

On rebooting, Module 1 automatically starts the softap, waits for a message on port 8000 and enters stream mode. Data sent to the Module 1 UART is transmitted over the softap interface. However a message from Module 2 is required before Module 1 knows the client address and port.

Now, copy and paste the commands in the left hand column of the following table into a Gecko OS terminal connected to Module 2.

Module 2 UDP Client Configuration Settings #

set wlan.ssid                   test1ssid
set wlan.passkey                test1secretkey
set wlan.auto_join.enabled      1

set udp.client.auto_interface   wlan
set udp.client.auto_start       1
set udp.client.remote_host      10.10.10.1
set udp.client.remote_port      8000

set bus.mode                    stream

save
reboot

<- Set name of Wi-Fi AP to join
<- Set passkey to use for Wi-Fi AP
<- Turn on wlan auto-join

<- UDP client uses wlan interface
<- UDP client connects automatically
<- Set server host for UDP client auto-connect
<- Set server port for UDP client auto-connect

<- Use serial bus stream mode

<- Save settings to flash
<- Reboot the module

On rebooting, Module 2 automatically connects to the Module 1 softap and enters stream mode. Data sent to the Module 1 UART is transmitted over the wlan interface. On Module 2 sending the first message, Module 1 stores the IP and port of Module 2 for later responses to Module 1.

UDP Wireless Magic! #

Type characters into the client (Module 2) Gecko OS terminal. They appear immediately on the Module 1 Gecko OS terminal.

Now type characters into the server (Module 1) Gecko OS terminal. They appear immediately on the Module 2 Gecko OS terminal.

Note : Because UDP is a connectionless protocol, the client must send the first message. Then the server records the address of the client and can respond. If you type first on the Module 1 Gecko OS terminal, there is no response at the Module 2 Gecko OS terminal because the server has no record of a client.

If this is a problem, you can simply set up both modules with a UDP server configuration. See below.

Wireless Serial Port using UDP Symmetrical Server Configuration #

UDP is a connectionless protocol, so the terms server and client are used loosely. With Gecko OS, the difference is that a module configured as a UDP server has more options, such as a configurable UDP server port, and some server behavior based on expecting a communication from a client.

If you want either module to be capable of receiving the first communication, just set up both as servers.

Module 1 still runs the softap, but Module 2 has a static IP address and DHCP is not required.

Instead of using a client lock, Module 1 is hard coded with the known IP address and port of Module 2.

Module 1 UDP Server Configuration Settings #

set softap.auto_start           1
set softap.dhcp_server.enabled  0
set softap.ssid                 test1ssid
set softap.passkey              test1secretkey

set udp.server.auto_interface   softap
set udp.server.auto_start       1
set udp.server.port             8000
set udp.server.remote_host      10.10.10.2
set udp.server.remote_port      8008

set bus.mode                    stream

save
reboot

<- softap auto starts on reboot
<- DHCP server is disabled
<- Set server softap name
<- Set server softap passkey

<- UDP server uses softAP interface
<- UDP server auto starts on reboot
<- UDP server port
<- Known IP address for Module 2
<- Known port for Module 2

<- Use serial bus stream mode

<- Save settings to flash
<- Reboot the module

On rebooting, Module 1 automatically starts the softap, waits for a UDP message on port 8000 and enters stream mode. Data sent to the Module 1 UART is transmitted over the softap interface to the configured remote host and remote port.

Module 2 UDP Server Configuration Settings #

set wlan.ssid                   test1ssid
set wlan.passkey                test1secretkey
set wlan.auto_join.enabled      1

set wlan.dhcp.enabled        0
set wlan.static.ip              10.10.10.2

set udp.server.auto_interface   wlan
set udp.server.auto_start       1
set udp.server.port             8008
set udp.server.remote_host      10.10.10.1
set udp.server.remote_port      8000

set bus.mode                    stream

save
reboot

<- Set name of Wi-Fi AP to join
<- Set passkey to use for Wi-Fi AP
<- Turn on wlan auto-join

<- Do not use DHCP to obtain IP address
<- Set static IP address, known to Module 1

<- UDP client uses wlan interface
<- UDP client connects automatically
<- Set port, known to Module 1
<- Set Module 1 address for UDP auto-connect
<- Set Module 1 port for UDP auto-connect

<- Use serial bus stream mode

<- Save settings to flash
<- Reboot the module

On rebooting, Module 2 sets its static IP, joins the WLAN, waits for a UDP message on port 8008 and enters stream mode. Data sent to the Module 2 UART is transmitted over the wlan interface to the configured remote host and remote port.

More UDP Wireless Magic! #

Type characters into the Module 1 Gecko OS terminal. They appear immediately on the Module 2 Gecko OS terminal.

Alternatively, type characters into the Module 2 Gecko OS terminal. They appear immediately on the Module 1 Gecko OS terminal.

You can send the first message from either module.

High Speed Connections #

The above communications take place with the default UART settings of 115200 baud and no flow control. This is appropriate for a demonstration at human typing speeds. It is possible to use a similar system for high speed communications, for example at UART speeds above 1 Megabaud. In this case it is necessary to configure flow control.

See the High Speed UART app note for examples of configuring baud rates and setting flow control.

Supporting Gecko OS Versions #

• Gecko OS 4

Change Log #