TWAI: Add receive example

This commit addes an example showing how to receive messages using the TWAI
driver interface and a CAN transceiver. Specifically, the example demonstrates:

- How to configure and install the TWAI drvier
- How to poll for TWAI events (i.e., alerts) using twai_read_alerts()
- How to handle the various events (such as TWAI_ALERT_RX_DATA)

Closes #7430

Author: designer2k2

libraries/ESP32/examples/TWAI/TWAIreceive/TWAIreceive.ino

@@ -0,0 +1,127 @@
+/* ESP32 TWAI receive example.
+  Receive messages and sends them over serial.
+
+  Connect a CAN bus transceiver to the RX/TX pins.
+  For example: SN65HVD230
+
+  TWAI_MODE_LISTEN_ONLY is used so that the TWAI controller will not influence the bus.
+
+  The API gives other possible speeds and alerts:
+  https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/peripherals/twai.html
+
+  Example output from a can bus message:
+  -> Message received
+  -> Message is in Standard Format
+  -> ID: 604
+  -> Byte: 0 = 00, 1 = 0f, 2 = 13, 3 = 02, 4 = 00, 5 = 00, 6 = 08, 7 = 00
+
+  Example output with alerts:
+  -> Alert: A (Bit, Stuff, CRC, Form, ACK) error has occurred on the bus.
+  -> Bus error count: 171
+  -> Alert: The RX queue is full causing a received frame to be lost.
+  -> RX buffered: 4  RX missed: 46 RX overrun 0
+
+  created 05-11-2022 by Stephan Martin (designer2k2)
+*/
+
+#include "driver/twai.h"
+
+// Pins used to connect to CAN bus transceiver:
+#define RX_PIN 21
+#define TX_PIN 22
+
+// Intervall:
+#define POLLING_RATE_MS 1000
+
+static bool driver_installed = false;
+
+void setup() {
+  // Start Serial:
+  Serial.begin(115200);
+
+  // Initialize configuration structures using macro initializers
+  twai_general_config_t g_config = TWAI_GENERAL_CONFIG_DEFAULT((gpio_num_t)TX_PIN, (gpio_num_t)RX_PIN, TWAI_MODE_LISTEN_ONLY);
+  twai_timing_config_t t_config = TWAI_TIMING_CONFIG_500KBITS();  //Look in the api-reference for other speed sets.
+  twai_filter_config_t f_config = TWAI_FILTER_CONFIG_ACCEPT_ALL();
+
+  // Install TWAI driver
+  if (twai_driver_install(&g_config, &t_config, &f_config) == ESP_OK) {
+    Serial.println("Driver installed");
+  } else {
+    Serial.println("Failed to install driver");
+    return;
+  }
+
+  // Start TWAI driver
+  if (twai_start() == ESP_OK) {
+    Serial.println("Driver started");
+  } else {
+    Serial.println("Failed to start driver");
+    return;
+  }
+
+  // Reconfigure alerts to detect frame receive, Bus-Off error and RX queue full states
+  uint32_t alerts_to_enable = TWAI_ALERT_RX_DATA | TWAI_ALERT_ERR_PASS | TWAI_ALERT_BUS_ERROR | TWAI_ALERT_RX_QUEUE_FULL;
+  if (twai_reconfigure_alerts(alerts_to_enable, NULL) == ESP_OK) {
+    Serial.println("CAN Alerts reconfigured");
+  } else {
+    Serial.println("Failed to reconfigure alerts");
+    return;
+  }
+
+  // TWAI driver is now successfully installed and started
+  driver_installed = true;
+}
+
+static void handle_rx_message(twai_message_t& message) {
+  // Process received message
+  if (message.extd) {
+    Serial.println("Message is in Extended Format");
+  } else {
+    Serial.println("Message is in Standard Format");
+  }
+  Serial.printf("ID: %x\nByte:", message.identifier);
+  if (!(message.rtr)) {
+    for (int i = 0; i < message.data_length_code; i++) {
+      Serial.printf(" %d = %02x,", i, message.data[i]);
+    }
+    Serial.println("");
+  }
+}
+
+void loop() {
+  if (!driver_installed) {
+    // Driver not installed
+    Serial.println("TWAI driver not installed!");
+    return;
+  }
+  // Check if alert happened
+  uint32_t alerts_triggered;
+  twai_read_alerts(&alerts_triggered, pdMS_TO_TICKS(POLLING_RATE_MS));
+  twai_status_info_t twaistatus;
+  twai_get_status_info(&twaistatus);
+
+  // Handle alerts
+  if (alerts_triggered & TWAI_ALERT_ERR_PASS) {
+    Serial.println("Alert: TWAI controller has become error passive.");
+  }
+  if (alerts_triggered & TWAI_ALERT_BUS_ERROR) {
+    Serial.println("Alert: A (Bit, Stuff, CRC, Form, ACK) error has occurred on the bus.");
+    Serial.printf("Bus error count: %d\n", twaistatus.bus_error_count);
+  }
+  if (alerts_triggered & TWAI_ALERT_RX_QUEUE_FULL) {
+    Serial.println("Alert: The RX queue is full causing a received frame to be lost.");
+    Serial.printf("RX buffered: %d\t", twaistatus.msgs_to_rx);
+    Serial.printf("RX missed: %d\t", twaistatus.rx_missed_count);
+    Serial.printf("RX overrun %d\n", twaistatus.rx_overrun_count);
+  }
+
+  // Check if message is received
+  if (alerts_triggered & TWAI_ALERT_RX_DATA) {
+    // One or more messages received. Handle all.
+    twai_message_t message;
+    while (twai_receive(&message, 0) == ESP_OK) {
+      handle_rx_message(message);
+    }
+  }
+}