Wi-Fi

This document describes Terragraph's Wi-Fi architecture on Puma.

Overview

Puma uses an ESP32 chip (ESP32-WROOM-32U) from Espressif Systems for Wi-Fi. Two serial ports are used:

• /dev/ttyS0 - Linux console access via Telnet
• /dev/ttyS2 - SLIP port

The following IP addresses are configured by default:

IP Address	Description
192.168.4.1	Wi-Fi AP
192.168.4.x	Client/station IP assigned by ESP32 DHCP
192.168.5.2	SLIP interface endpoint in ESP32
192.168.5.1	SLIP interface endpoint in NXP

Wi-Fi is only used for administrative purposes and does not carry any user traffic.

ESP32 Firmware

The ESP32 firmware is built via recipes-wifi/esp-fw/esp-fw_0.1.bb. This uses ESP-IDF, the official development framework. Sources are located in recipes-wifi/esp-fw/files/src/.

Updating ESP32 firmware is done through the following scripts:

• make_esp32_cfg.sh - Generates the binary config-partition image (esp32config.bin)
• flash_esp32.sh - Flashes the application, configuration, etc.

The default firmware binaries are installed in /usr/share/esp32/:

Binary	Purpose
bootloader.bin	bootloader
partitions_singleapp.bin	partition table
wifi_softAP.bin	application

Telnet

The ESP32 firmware includes a Telnet listener which accepts connections on 192.168.4.1. This can be used to access the Linux console. To disable the serial console altogether (not only over Wi-Fi), use the node configuration field envParams.SERIAL_CONSOLE_DISABLE.

SLIP

SLIP (Serial Line Internet Protocol) is used to enable TCP/IP on the serial port /dev/ttyS2. This is configured via node configuration keys envParams.SLIP_*, along with two sv services installed through recipes-wifi/esp-slip/esp-slip_0.1.bb:

• slip - wrapper for slattach
• slip_route - IP configuration (run once)

SLIP speeds are limited based on the configured baud rate. This is 115200 by default, but can be increased to 576000 (through a patch to slattach in recipes-extended/net-tools/files/0000-Add-higher-baud-rates.patch).

Resources

• ESP-IDF - Espressif IoT Development Framework