Project 8: UART Telemetry Hub - Reliable Serial Diagnostics

Build a structured UART telemetry protocol with buffering, checksums, and host parsing.

Quick Reference

Attribute Value
Difficulty Level 1: Beginner
Time Estimate 4-8 hours
Main Programming Language C++
Alternative Programming Languages C
Coolness Level Level 2: Practical but solid
Business Potential 2. The “Support” Model
Prerequisites C/C++ basics, Teensyduino setup, basic electronics, ability to use a multimeter/logic analyzer
Key Topics UART framing, buffering, checksums

1. Learning Objectives

By completing this project, you will:

  1. Explain the core question for this project in your own words.
  2. Implement the main workflow and validate it with measurements.
  3. Handle at least two failure modes and document recovery.
  4. Produce a deterministic report that matches hardware behavior.

2. All Theory Needed (Per-Concept Breakdown)

UART Framing, Buffers, and Robust Telemetry

Fundamentals UART is asynchronous serial communication with start/stop bits and optional parity. Because there is no shared clock, baud accuracy matters. Reliability depends on correct framing, buffering, and error handling. A telemetry hub is a structured protocol, not just a stream of print statements.

Deep Dive into the concept UART frames are timed by the receiver’s baud clock. If baud rates differ too much, the receiver samples bits at the wrong times and framing errors occur. This risk increases at higher baud. Buffers decouple interrupt-driven receive from slower parsing logic. A ring buffer prevents data loss when parsing lags. On transmit, buffering avoids blocking critical code. A robust telemetry protocol includes a header, length, message type, and checksum. These allow resynchronization after errors and detection of corruption. Logging error counters for framing and CRC failures makes the system observable. This project builds that full path: firmware framing, host parsing, and deterministic logs.

How this fit on projects This concept directly powers the implementation choices and validation steps in this project.

Definitions & key terms

  • Baud rate: Symbols per second on the UART line.
  • Framing error: Receiver did not see a valid stop bit.
  • Ring buffer: Circular buffer used to store streaming data.
  • Parity: Optional error-checking bit in UART frames.

Mental model diagram (ASCII)

TX -> UART line -> RX buffer -> Parser

How it works (step-by-step)

  1. Configure UART baud rate and frame format.
  2. Implement RX ring buffer with overflow detection.
  3. Define message framing and checksum.
  4. Log and parse telemetry on the host.

Minimal concrete example

Serial1.begin(115200);
if (Serial1.available()) { int b = Serial1.read(); }

Common misconceptions

  • Serial print is always safe inside ISRs.
  • Baud mismatch doesn’t matter at low speeds.
  • A newline is enough framing for binary data.

Check-your-understanding questions

  • How does baud error accumulate over a frame?
  • Why do you need a ring buffer?
  • What is a good resync strategy?

Check-your-understanding answers

  • Sampling drift grows each bit and can miss the stop bit.
  • Without it, data is dropped when parsing is slow.
  • Use a fixed header marker and length field.

Real-world applications

  • Debug consoles
  • Telemetry links
  • Bootloader communication

Where you’ll apply it

References

  • UART chapter in MCU reference manual
  • Embedded protocol design notes

Key insights

Reliable UART is about buffering and framing, not just baud rate.

Summary

A telemetry hub is a structured protocol with deterministic logs.

Homework/Exercises to practice the concept

  • Inject a framing error and verify resync.
  • Measure buffer overflow rate at high message rates.

Solutions to the homework/exercises

  • Toggle a pin on framing error interrupt and count occurrences.
  • Increase message rate until overflow and log the threshold.

3. Project Specification

3.1 What You Will Build

Build a structured UART telemetry protocol with buffering, checksums, and host parsing.

3.2 Functional Requirements

  1. Implement ring buffers for RX/TX.
  2. Define framed messages with length and checksum.
  3. Build a host-side parser script.
  4. Log error counters and resync events.

3.3 Non-Functional Requirements

  • Performance: Meet the target timing/throughput for the project.
  • Reliability: Detect errors and recover without undefined behavior.
  • Usability: Provide clear logs and a repeatable workflow.

3.4 Example Usage / Output

./P08-uart-telemetry-hub-reliable-serial-diagnostics --run

3.5 Data Formats / Schemas / Protocols

Frame: [0xAA][len][type][payload][crc16]

3.6 Edge Cases

  • Dropped bytes in middle of frame
  • Baud mismatch causing framing errors
  • Buffer overflow at high rates

3.7 Real World Outcome

You will run the project and see deterministic logs and measurements that match physical hardware behavior.

3.7.1 How to Run (Copy/Paste)

cd project-root
make
./P08-uart-telemetry-hub-reliable-serial-diagnostics --run

3.7.2 Golden Path Demo (Deterministic)

Use a fixed input configuration and a known test signal. Capture output for 60 seconds and verify it matches expected values.

3.7.3 If CLI: exact terminal transcript

$ ./P08-uart-telemetry-hub-reliable-serial-diagnostics --run --seed 42
[INFO] UART Telemetry Hub - Reliable Serial Diagnostics starting
[INFO] Report saved to data/report.csv
[INFO] Status: OK
$ echo $?
0

Failure Demo (Deterministic)

$ ./P08-uart-telemetry-hub-reliable-serial-diagnostics --run --missing-device
[ERROR] Device not detected
$ echo $?
2

4. Solution Architecture

4.1 High-Level Design

Inputs -> Acquisition -> Processing -> Output/Log

4.2 Key Components

Component Responsibility Key Decisions
Acquisition Configure peripherals and capture data Use stable clock settings
Processing Convert raw data to meaningful values Apply calibration/filters
Output/Log Emit reports and logs CSV for reproducibility

4.3 Data Structures (No Full Code)

struct Sample {
    uint32_t timestamp_us;
    uint32_t value;
    uint32_t flags;
};

4.4 Algorithm Overview

Key Algorithm: Measurement + Report

  1. Initialize hardware and verify configuration.
  2. Capture data and record timestamps.
  3. Compute metrics and write report.

Complexity Analysis:

  • Time: O(n) in samples
  • Space: O(n) for log storage

5. Implementation Guide

5.1 Development Environment Setup

# Arduino IDE + Teensyduino must be installed
# Optional CLI workflow
arduino-cli core update-index
arduino-cli core install teensy:avr

5.2 Project Structure

project-root/
├── src/
│   ├── main.ino
│   ├── hw_config.h
│   └── measurements.cpp
├── tools/
│   └── analyze.py
├── data/
│   └── samples.csv
└── README.md

5.3 The Core Question You’re Answering

“How do I make serial telemetry robust and parseable?”

5.4 Concepts You Must Understand First

Stop and research these before coding:

  1. UART framing, buffering, checksums
  2. Data logging and measurement techniques
  3. Basic timing math and error analysis

5.5 Questions to Guide Your Design

  1. What framing marker will you use?
  2. How will you recover after a bad checksum?
  3. How large should your buffers be?

5.6 Thinking Exercise

Design a minimal frame format that can recover from byte loss.

5.7 The Interview Questions They’ll Ask

  1. What causes framing errors?
  2. Why use a ring buffer?
  3. How do you handle flow control?

5.8 Hints in Layers

  • Start with a simple fixed header byte.
  • Add CRC after the protocol is stable.
  • Log buffer high-water marks.

5.9 Books That Will Help

| Topic | Book | Chapter | |——-|——|———| | Serial basics | Arduino Workshop | Ch. 7 | | Embedded comms | Making Embedded Systems | Ch. 6 | | Checksum design | Serial Communications | Ch. 3 |

5.10 Implementation Phases

Phase 1: Foundation (2 hours)

Goals:

  • Implement ring buffer
  • Send simple frames

Tasks:

  1. Implement ring buffer
  2. Send simple frames

Checkpoint: Frames visible on host

Phase 2: Core Functionality (4 hours)

Goals:

  • Add CRC
  • Implement parser

Tasks:

  1. Add CRC
  2. Implement parser

Checkpoint: Reliable telemetry

Phase 3: Polish (2 hours)

Goals:

  • Add error counters
  • Document protocol

Tasks:

  1. Add error counters
  2. Document protocol

Checkpoint: Telemetry spec done

5.11 Key Implementation Decisions

| Decision | Options | Recommendation | Rationale | |———-|———|—————-|———–| | Buffering | Single buffer, double buffer | Double buffer | Avoids data loss during processing | | Logging format | CSV, binary | CSV | Human-readable while still scriptable | | Clock speed | Default, overclock | Default | Keeps peripherals in spec |

6. Testing Strategy

6.1 Test Categories

| Category | Purpose | Examples | |———-|———|———-| | Unit Tests | Validate math, parsing, and conversions | Timer math, CRC checks | | Integration Tests | Verify peripherals and pipelines | DMA -> buffer -> log | | Edge Case Tests | Handle boundary conditions | Brownout, missing sensor |

6.2 Critical Test Cases

{test_cases}

6.3 Test Data

Use a fixed test input pattern and record outputs to data/report.csv

7. Common Pitfalls & Debugging

7.1 Frequent Mistakes

| Pitfall | Symptom | Solution | |———|———|———-| {pitfalls}

7.2 Debugging Strategies

{debug_strats}

7.3 Performance Traps

Large buffers improve stability but increase latency. Measure both throughput and jitter to choose the right size.

8. Extensions & Challenges

8.1 Beginner Extensions

{ex_begin}

8.2 Intermediate Extensions

{ex_inter}

8.3 Advanced Extensions

{ex_adv}

9. Real-World Connections

9.1 Industry Applications

{industry_apps}

{open_source}

9.3 Interview Relevance

{interview_rel}

10. Resources

10.1 Essential Reading

{resources}

10.2 Video Resources

  • Embedded systems timing walkthrough (YouTube)
  • Teensy hardware deep dive (Conference talk)

10.3 Tools & Documentation

  • Teensyduino: Toolchain for Teensy boards
  • Logic Analyzer: Timing verification
  • Multimeter: Voltage and current measurement

{related_projects}

11. Self-Assessment Checklist

11.1 Understanding

  • I can explain the main concept without notes.
  • I can explain why the measurements match (or do not match) expectations.
  • I understand at least one tradeoff made in this project.

11.2 Implementation

  • All functional requirements are met.
  • All critical test cases pass.
  • Logs and reports are reproducible.
  • Edge cases are handled.

11.3 Growth

  • I documented lessons learned.
  • I can explain this project in a job interview.
  • I identified one improvement for next iteration.

12. Submission / Completion Criteria

Minimum Viable Completion: {comp_min}

Full Completion: {comp_full}

Excellence (Going Above & Beyond): {comp_ex}