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:
* 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:
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:
1. Both master and slave go through install and start their TWAI drivers independently.
2. 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.
3. Once the master has received the **PING_RESP** from the slave, it will send a **START_CMD** message to the slave.
4. 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).
