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README.md

TWAI Network Example

(See the README.md file in the upper level 'examples' directory for more information about examples.)

This example demonstrates how to use the TWAI driver to program a target (ESP32, ESP32-S2, ESP32-S3 or ESP32-C3) as a TWAI node, and have the two nodes (Network Master and Network Slave) communicate on a TWAI network. The Listen Only node is optional and acts as a network monitor meaning that it only receives messages and does not influence the bus in any way (i.e. doesn't not acknowledge or send error frames).

Note that concept of master/slave in this example refers to which node initiates and stops the transfer of a stream of data messages.

How to use example

Hardware Required

This example requires at least two targets (e.g., an ESP32 or ESP32-S2) to act as the Network Master and Network Slave. The third target (Listen Only) is optional. Each target must be connected to an external transceiver (e.g., a SN65HVD23X transceiver). The transceivers must then be interconnected to form a TWAI network.

The following diagram illustrates an example network:

    ----------   ----------   --------------
   |  Master  | |  Slave   | | Listen Only  |
   |          | |          | |              |
   | TX    RX | | TX    RX | | TX    RX     |
    ----------   ----------   --------------
     |      |     |      |     |      |
     |      |     |      |     |      |
    ----------   ----------   ----------
   | D      R | | D      R | | D      R |
   |          | |          | |          |
   |  VP230   | |  VP230   | |  VP230   |
   |          | |          | |          |
   | H      L | | H      L | | H      L |
    ----------   ----------   ----------
     |      |     |      |     |      |
     |      |     |      |     |      |
  |--x------|-----x------|-----x------|--| H
            |            |            |
  |---------x------------x------------x--| L

Note: If you don't have an external transceiver, you can still run the TWAI Self Test example

Configure the project

For each node in the TWAI network (i.e., Master, Slave, Listen Only)...

Set the target of the build (where {IDF_TARGET} stands for the target chip such as eszp32 or esp32s2).
Then run menuconfig to configure the example.

idf.py set-target {IDF_TARGET}
idf.py menuconfig

Under Example Configuration, configure the pin assignments using the options TX GPIO Number and RX GPIO Number according to how the target was connected to the transceiver. By default, TX GPIO Number and RX GPIO Number are set to the following values:
- On the ESP32, TX GPIO Number and RX GPIO Number default to 21 and 22 respectively
- On the ESP32-S2, TX GPIO Number and RX GPIO Number default to 20 and 21 respectively
- On the ESP32-S3, TX GPIO Number and RX GPIO Number default to 20 and 21 respectively
- On the ESP32-C3, TX GPIO Number and RX GPIO Number default to 2 and 3 respectively

Build and Flash

For each node, build the project and flash it to the board, then run monitor tool to view serial output:

idf.py -p PORT flash monitor

(Replace PORT with the name of the serial port to use.)

(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

Network Master

I (345) TWAI Master: Driver installed
I (345) TWAI Master: Driver started
I (345) TWAI Master: Transmitting ping
I (3105) TWAI Master: Transmitted start command
I (3105) TWAI Master: Received data value 339
...
I (5545) TWAI Master: Received data value 584
I (5545) TWAI Master: Transmitted stop command
I (5595) TWAI Master: Driver stopped
I (6595) TWAI Master: Driver started
I (6595) TWAI Master: Transmitting ping
I (7095) TWAI Master: Transmitted start command
I (7095) TWAI Master: Received data value 738
...
I (9535) TWAI Master: Received data value 983
I (9535) TWAI Master: Transmitted stop command
I (9585) TWAI Master: Driver stopped
I (10585) TWAI Master: Driver started
I (10585) TWAI Master: Transmitting ping
I (11085) TWAI Master: Transmitted start command
I (11085) TWAI Master: Received data value 1137
...
I (13525) TWAI Master: Received data value 1382
I (13525) TWAI Master: Transmitted stop command
I (13575) TWAI Master: Driver stopped
I (14575) TWAI Master: Driver uninstalled

Network Slave

Slave starting in 3
Slave starting in 2
Slave starting in 1
I (6322) TWAI Slave: Driver installed
I (6322) TWAI Slave: Driver started
I (6462) TWAI Slave: Transmitted ping response
I (6712) TWAI Slave: Start transmitting data
I (6712) TWAI Slave: Transmitted data value 339
...
I (9162) TWAI Slave: Transmitted data value 584
I (9212) TWAI Slave: Transmitted stop response
I (9312) TWAI Slave: Driver stopped
I (10312) TWAI Slave: Driver started
I (10452) TWAI Slave: Transmitted ping response
I (10702) TWAI Slave: Start transmitting data
I (10702) TWAI Slave: Transmitted data value 738
...
I (13152) TWAI Slave: Transmitted data value 983
I (13202) TWAI Slave: Transmitted stop response
I (13302) TWAI Slave: Driver stopped
I (14302) TWAI Slave: Driver started
I (14442) TWAI Slave: Transmitted ping response
I (14692) TWAI Slave: Start transmitting data
I (14692) TWAI Slave: Transmitted data value 1137
...
I (17142) TWAI Slave: Transmitted data value 1382
I (17192) TWAI Slave: Transmitted stop response
I (17292) TWAI Slave: Driver stopped
I (18292) TWAI Slave: Driver uninstalled

Network Listen Only

I (326) TWAI Listen Only: Driver installed
I (326) TWAI Listen Only: Driver started
I (366) TWAI Listen Only: Received master ping
...
I (1866) TWAI Listen Only: Received master ping
I (1866) TWAI Listen Only: Received slave ping response
I (2116) TWAI Listen Only: Received master start command
I (2116) TWAI Listen Only: Received data value 329
...
I (4566) TWAI Listen Only: Received data value 574
I (4566) TWAI Listen Only: Received master stop command
I (4606) TWAI Listen Only: Received slave stop response
I (5606) TWAI Listen Only: Received master ping
I (5856) TWAI Listen Only: Received master ping
I (5856) TWAI Listen Only: Received slave ping response
I (6106) TWAI Listen Only: Received master start command
I (6106) TWAI Listen Only: Received data value 728
...
I (8556) TWAI Listen Only: Received data value 973
I (8556) TWAI Listen Only: Received master stop command
I (8596) TWAI Listen Only: Received slave stop response
I (9596) TWAI Listen Only: Received master ping
I (9846) TWAI Listen Only: Received master ping
I (9846) TWAI Listen Only: Received slave ping response
I (10096) TWAI Listen Only: Received master start command
I (10096) TWAI Listen Only: Received data value 1127
...
I (12546) TWAI Listen Only: Received data value 1372
I (12546) TWAI Listen Only: Received master stop command
I (12586) TWAI Listen Only: Received slave stop response
I (12586) TWAI Listen Only: Driver stopped
I (12586) TWAI Listen Only: Driver uninstalled

Example Breakdown

The communication between the Network Master and Network Slave execute the following steps over multiple iterations:

Both master and slave go through install and start their TWAI drivers independently.
The master repeatedly sends PING messages until it receives a PING_RESP (ping response message) from the slave. The slave will only send a PING_RESP message when it receives a PING message from the master.
Once the master has received the PING_RESP from the slave, it will send a START_CMD message to the slave.
Upon receiving the START_CMD message, the slave will start transmitting DATA messages until the master sends a STOP_CMD. The master will send the STOP_CMD after receiving N DATA messages from the slave (N = 50 by default).
When the slave receives the STOP_CMD, it will confirm that it has stopped by sending a STOP_RESP message to the master.