Nested loop doesn't iterate

Question

I am trying to brute force a CANBUS with ID's and values but my loop doesn't seem to change the ID.

I am expecting the following when changing ID's

0x100 FF FF FF FF FF FF FF FF
0x101 00 00 00 00 00 00 00 00

But I get

0x100 FF FF FF FF FF FF FF FF
0x100 00 00 00 00 00 00 00 00

I am not sure where I am going wrong

#include <SPI.h>
#include "mcp_can.h"

// Define the chip select pin for the MCP2515
#define CAN_CS 5

MCP_CAN CAN(CAN_CS); // Initialize MCP2515 with the CS pin

void setup() {
  Serial.begin(115200);

  // Initialize MCP2515
  if (CAN.begin(MCP_ANY, CAN_500KBPS, MCP_8MHZ) == CAN_OK) {
    Serial.println("MCP2515 Initialized Successfully!");
  } else {
    Serial.println("Error Initializing MCP2515...");
    while (1);
  }

  CAN.setMode(MCP_NORMAL);
}

void loop() {
  for (uint16_t id = 0x100; id <= 0x500; id++) { // Increment ID
    for (uint8_t byteValue = 0x00; byteValue <= 0xFF; byteValue++) { // Increment data bytes from 0x00 to 0xFF
      uint8_t data[8] = {byteValue, byteValue, byteValue, byteValue, byteValue, byteValue, byteValue, byteValue}; // Set all bytes to the current value

      // Send CAN message
      byte sendStatus = CAN.sendMsgBuf(id, 0, 8, data);

      // Keep the if condition unchanged
      if (sendStatus == CAN_OK) {
        Serial.print("Sent message with ID: 0x");
        Serial.print(id, HEX);
        Serial.print(" Data: ");
        for (int k = 0; k < 8; k++) {
          Serial.print(data[k], HEX);
          Serial.print(" ");
        }
        Serial.println();
      } else {
        Serial.print("Error sending message with ID: 0x");
        Serial.println(id, HEX);
      }

      delay(10); // Small delay between messages
    }

    // Print a separator after finishing all data bytes for the current ID
    Serial.println("----------------------------------------");
  }

  Serial.println("Finished all IDs from 0x100 to 0x500 with data bytes from 0x00 to 0xFF.");
  while (1); // Stop after completion
}

Answer 1

You outer loop "is not incrementing" might mean your inner loop never ends:

for (uint8_t byteValue = 0x00; byteValue <= 0xFF; byteValue++) {

Now what do we have in your for loop code:

• uint8_t byteValue -> byteValue can store values from 0 to 255 (0xFF)
• byteValue <= 0xFF -> maximum value is 255 and condition is basically less than 256 -> it's always true.
• uint8_t overflow is well defined 255+1 == 0 (unlike signed values)

Edit:

I tried to compile this loop and even without verbose compilation in the Arduino IDE it shows:

sketch_jan25a.ino: In function 'void loop()':
sketch_jan25a.ino:8:46: warning: comparison is always true due to limited range of data type [-Wtype-limits]

So don't ignore warnings in your code (there are also some warnings in Arduino core :D)