Basic TCP Client Example

A TCP client that transmits sensor data to a remote TCP server

SDK directory: apps/basic/tcp_client
Zentri App Store: ZENTRI-BATCPCLIENT

API Features Demonstrated

Platforms

This app works on:

AMW004 - Zentri Mackerel evaluation board
AMW106 - Zentri Moray evaluation board

Requirements and Prerequisites

This app requires a ZentriOS device with a thermistor and ADC, such as an AMW106-E03 Moray evaluation board.

Resources

The initialization file settings.ini is packaged with the app and downloaded to the device.

Description

This app connects to the Zentri test echo server at test.zentri.com, and transmits GPIO data and ADC data from the thermistor. Data is echoed back to the app and printed on the ZentriOS terminal.

Usage Instructions

Open a ZentriOS serial terminal to the device. See Getting Started, Opening a ZentriOS Terminal.

This app assumes your ZentriOS device is set up with the credentials to join your local network. If you have not already set up network credentials, on the ZentriOS terminal, run the commands:

network_up -s
save

See the Wi-Fi Command API documentation for network_up and save.

No interaction is required. Output is similar to:

> Network is down - Restarting Network...

Attempting to connect to test.zentri.com:50007
Connected. Socket handle: 0
Network down
Network up
Attempting to connect to test.zentri.com:50007
Connected. Socket handle: 1
Rx data: gpios:F5DA, adc: 1642mV
Rx data: gpios:35DA, adc: 1641mV
Rx data: gpios:35DE, adc: 1642mV

Implementation

In zn_app_init:

zn_load_app_settings("settings.ini") loads and runs the initialization file.
zn_adc_init(PLATFORM_THERMISTOR) initializes the ADC with the platform configuration for the thermistor.
zn_network_register_event_handler registers the function wlan_network_event_handler to handle network events.

In wlan_network_event_handler:

if the network is not up the handler issues the zn_network_up command to bring the network up.
if the network is already up, the handler issues a tcp_attempt_connect_handler event to attempt connection to the TCP_HOST at test.zentri.com.

The tcp_attempt_connect_handler function, in response to the tcp_attempt_connect_handler event:

calls zn_tcp_connect to connect to TCP_HOST.
if the connection is unsuccessful, calls zn_event_register_timed to issue the tcp_attempt_connect_handler after ATTEMPT_CONNECT_PERIOD milliseconds, and returns
if the connection is successful,
- calls zn_tcp_register_client_event_handlers to register the disconnect handler tcp_disconnect_handler, and the data received handler tcp_receive_handler.
- calls zn_event_register_periodic to set up a periodic tcp_transmit_handler event

The tcp_disconnect_handler function, in response to a TCP disconnection event:

Attempts to display any remaining data with a call to tcp_receive_handler.
Cleans up by calling zn_tcp_disconnect on the connection handle.
Sets up an attempt to reconnect, calling zn_event_issue with the tcp_attempt_connection_handler event.

The tcp_receive_handler function, in response to a data received event:

Calls zn_tcp_read to read the data from the TCP stream handle until failure or no more data is available.
Logs the data read to the ZentriOS terminal console.

Note that the data received is echoed from the ZentriOS echo server: ADC data sent in response to the periodic tcp_transmit_handler event.

The tcp_transmit_handler function, in response to a periodic tcp_transmit_handler event,

calls zn_gpio_mask_get with a mask of 0xFFFF to retrieve all available GPIO values
calls the zn_adc_sample function to retrieve thermistor data from the ADC
formats the data into an output string
calls zn_tcp_write to write the data to the TCP stream.

Source

See:

tcp_client.c