eth2ap Example

(See the README.md file in the upper level 'examples' directory for more information about examples. To try a more complex application about Ethernet to WiFi data forwarding, please go to iot-solution.)

Overview

The similarities on MAC layer between Ethernet and Wi-Fi make it easy to forward packets from Ethernet to Wi-Fi and vice versa. This example illustrates how to implement a simple "router" which only supports forwarding packets between Ethernet port and Wi-Fi AP interface. In this case, the Ethernet should play the role of WAN (i.e. it can access outside network) so that a mobile device could get access to the Internet when it gets connected to ESP32 through Wi-Fi.

Note: In this example, ESP32 works like a bridge between Ethernet and Wi-Fi, and it won't perform any actions on Layer3 and higher layer, which means there's no need to initialize the TCP/IP stack.

How to use this example

Hardware Required

To run this example, it's recommended that you have an official ESP32 Ethernet development board - ESP32-Ethernet-Kit. This example should also work for 3rd party ESP32 board as long as it's integrated with a supported Ethernet PHY chip. Up until now, ESP-IDF supports four Ethernet PHY: LAN8720, IP101, DP83848 and RTL8201, additional PHY drivers should be implemented by users themselves.

Project configuration in menuconfig

Enter make menuconfig if you are using GNU Make based build system or enter idf.py menuconfig if you' are using CMake based build system.

In the Example Configuration menu:

Choose PHY device under Ethernet PHY Device, by default, the ESP32-Ethernet-Kit has an IP101 on board.
Set the SSID and password for Wi-Fi ap interface under Wi-Fi SSID and Wi-Fi Password.
Set the maximum connection number under Maximum STA connections.

In the Component config > Ethernet menu:

Enable Use ESP32 internal EMAC controller, and then go into this menu.
In the PHY interface, it's highly recommended that you choose Reduced Media Independent Interface (RMII) which will cost fewer pins.
In the RMII clock mode, you can choose the source of RMII clock (50MHz): Input RMII clock from external or Output RMII clock from internal.
Once Output RMII clock from internal is enabled, you also have to set the number of the GPIO used for outputting the RMII clock under RMII clock GPIO number. In this case, you can set the GPIO number to 16 or 17.
Once Output RMII clock from GPIO0 (Experimental!) is enabled, then you have no choice but GPIO0 to output the RMII clock.
Set SMI MDC/MDIO GPIO number according to board schematic, by default these two GPIOs are set as below:

Default Example GPIO RMII Signal Notes

GPIO23 MDC Output to PHY

GPIO18 MDIO Bidirectional
If you have connect a GPIO to the PHY chip's RST pin, then you need to enable Use Reset Pin of PHY Chip and set the GPIO number under PHY RST GPIO number.

Default Example GPIO	RMII Signal	Notes
GPIO23	MDC	Output to PHY
GPIO18	MDIO	Bidirectional

Extra configuration in the code (Optional)

By default Ethernet driver will assume the PHY address to 1, but you can alway reconfigure this value after eth_phy_config_t phy_config = ETH_PHY_DEFAULT_CONFIG();. The actual PHY address should depend on the hardware you use, so make sure to consult the schematic and datasheet.peripheral (e.g. I²S), you'd better choose the external clock.

Build and Flash

To build and flash the example, enter make -j4 flash monitor if you are using GNU Make based build system or enter idf.py build flash monitor if you are using CMake based build system.

(To exit the serial monitor, type Ctrl-].)

See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.

Example Output

Step 1: Initialize Ethernet and Wi-Fi (AP mode)

I (508) example: Power On Ethernet PHY
I (518) system_api: Base MAC address is not set, read default base MAC address from BLK0 of EFUSE
I (518) emac: emac reset done
I (518) example: Ethernet Started
......
I (538) wifi: wifi driver task: 3ffc7fbc, prio:23, stack:3584, core=0
I (538) system_api: Base MAC address is not set, read default base MAC address from BLK0 of EFUSE
I (538) system_api: Base MAC address is not set, read default base MAC address from BLK0 of EFUSE
I (568) wifi: wifi firmware version: ec61a20
I (568) wifi: config NVS flash: enabled
I (568) wifi: config nano formating: disabled
I (568) wifi: Init dynamic tx buffer num: 32
I (568) wifi: Init data frame dynamic rx buffer num: 32
I (578) wifi: Init management frame dynamic rx buffer num: 32
I (588) wifi: Init management short buffer num: 32
I (588) wifi: Init static rx buffer size: 1600
I (588) wifi: Init static rx buffer num: 10
I (598) wifi: Init dynamic rx buffer num: 32

Step 2: Ethernet Connects to Router/Switch/PC (with DHCP server enabled)

I (4518) example: Ethernet Link Up

Step 3: Start Wi-Fi AP

I (4618) phy: phy_version: 4100, 2a5dd04, Jan 23 2019, 21:00:07, 0, 0
I (4618) wifi: mode : softAP (30:ae:a4:c6:87:5b)
I (4628) wifi: Total power save buffer number: 16
I (4628) wifi: Init max length of beacon: 752/752
I (4628) wifi: Init max length of beacon: 752/752

Step 4: Wi-Fi station (e.g. mobile phone) connects to ESP32's Wi-Fi

I (10168) wifi: new:<1,0>, old:<1,0>, ap:<1,1>, sta:<255,255>, prof:1
I (10168) wifi: station: c4:0b:cb:ec:9a:84 join, AID=1, bgn, 20
I (10258) example: AP got a station connected

Now your mobile phone should get access to the Internet.

Troubleshooting

RMII Clock
- ESP32's MAC and the external PHY device need a common 50MHz reference clock (aka RMII clock). This clock can either be provided by an externally oscillator or generated from internal APLL. The signal integrity of RMII clock is strict, so it is highly recommended to add a 33Ω resistor in series to reduce possible ringing.
- ESP32 can generate a 50MHz clock using internal APLL. But if the APLL is already used for other purposes (e.g. I2S peripheral), then you have no choice but use an external RMII clock.
GPIO connections
- RMII PHY wiring is fixed and can not be changed through either IOMUX or GPIO Matrix. They're described as below:
GPIO RMII Signal ESP32 EMAC Function

GPIO21 TX_EN EMAC_TX_EN

GPIO19 TX0 EMAC_TXD0

GPIO22 TX1 EMAC_TXD1

GPIO25 RX0 EMAC_RXD0

GPIO26 RX1 EMAC_RXD1

GPIO27 CRS_DV EMAC_RX_DRV
Got error message WiFi send packet failed when running the example.
- Ethernet process packets faster than Wi-Fi on ESP32, so have a try to enlarge the value of FLOW_CONTROL_WIFI_SEND_DELAY_MS.
Got error message send flow control message failed or timeout when running the example.
- Enlarge the length of FLOW_CONTROL_QUEUE_LENGTH.
Wi-Fi station doesn't receive any IP via DHCP.
- All Layer 3 (TCP/IP functions) on the ESP32 are disabled, including the SoftAP DHCP server. This means that devices must be able to access another DHCP server (for example on a Wi-Fi router connected via ethernet) or should use statically assigned IP addresses.

GPIO	RMII Signal	ESP32 EMAC Function
GPIO21	TX_EN	EMAC_TX_EN
GPIO19	TX0	EMAC_TXD0
GPIO22	TX1	EMAC_TXD1
GPIO25	RX0	EMAC_RXD0
GPIO26	RX1	EMAC_RXD1
GPIO27	CRS_DV	EMAC_RX_DRV

(For any technical queries, please open an issue on GitHub. We will get back to you as soon as possible.)

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