Week 11: Networking & Communications

This error message is a Python traceback, which shows the sequence of function calls that led to a crash in the program.

What is a Traceback?

A traceback is Python’s way of telling you where something went wrong. It shows the call stack: a list of all the functions that were running before the error occurred.

In your case:

The script prog.py from the megaTinyCore package tried to program an ATtiny chip using the UPDI interface. It failed with:

pymcuprog.pymcuprog_errors.PymcuprogError: UPDI initialisation failed

This means the tool couldn’t establish a connection to the microcontroller using UPDI (Unified Program and Debug Interface).

Possible Causes:

• Wrong COM port selected
• Incorrect programmer or board setting
• Missing or incorrect 4.7kΩ pull-up resistor
• Target microcontroller not powered
• Communication speed too high
• Chip might have UPDI disabled (fuse change)

How to Fix It:

• Double-check your wiring and power supply
• Select the correct COM port and programmer (e.g., jtag2updi)
• Use a 4.7kΩ resistor between TX and UPDI
• Lower the UPDI baud rate
• Make sure the chip hasn’t had UPDI disabled

A traceback is an error report generated by Python when something goes wrong during program execution.

Why it’s Called a "Traceback"

It “traces back” through the function calls that led to the error. This helps you understand where and why your code crashed.

What it Shows:

• File name and line number where the error occurred
• The exact function call hierarchy
• The type of error (e.g., ZeroDivisionError, TypeError, etc.)

Example:

                            Traceback (most recent call last):
                            File "main.py", line 10, in 
                                divide()
                            File "main.py", line 5, in divide
                                result = 1 / 0
                            ZeroDivisionError: division by zero
                                        

This example shows a division by zero inside a function called by the main program. The traceback tells you exactly where the problem occurred.

When you reduced the clock speed and changed the supply voltage, you made your ATtiny microcontroller more stable during UPDI communication.

Why Lower Clock Speed Helped:

• High speeds (like 20 MHz) make the chip more sensitive to voltage dips and noise.
• Lowering to 16 MHz reduces timing errors and makes UPDI sync more reliable.

Why 3.3V Supply Helped:

• Many ATtiny chips are optimized for 3.3V operation.
• If your UPDI programmer is 3.3V and the chip runs at 5V, you get voltage mismatch.
• 3.3V keeps logic levels compatible, reducing chances of failed communication.

Summary:

• ✅ Lower clock = more stability
• ✅ 3.3V supply = better compatibility with your UPDI programmer
• ✅ Easier for programmer to sync and upload code without errors

The error you're seeing is caused by trying to pass a string literal (a const char*) to the version of Wire.write() that only accepts a single byte (uint8_t). The function you're calling doesn't match any overloaded version that takes a string.

✅ How to Fix It:

Use the correct overloaded version of Wire.write() that accepts a byte array or string:

Wire.write((const uint8_t*)"x is ", 5);

Or, to make it dynamic and safe:

const char* message = "x is ";
                        Wire.write((const uint8_t*)message, strlen(message));

This tells the compiler explicitly that you're sending a pointer to a string and how many bytes to write.

🔍 Why It Matters:

• Wire.write(uint8_t) → expects a single byte (like a number or a character)
• Wire.write(const uint8_t*, size_t) → used to send strings or byte arrays