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Phase 3: I2C

Learning Objectives

  • I2C communication
  • Object-oriented programming in C++
  • Basic driver development
  • Fixed point data formatting
  • Waveform analysis with a logic analyzer

Summary

Now that you can communicate between the microcontroller (uC) and your computer, you can start playing with other communication protocols and report the results back over UART. The first one we'll cover is Inter-Integrated Circuit, abbreviated I2C, which is read as "eye-two-cee" or "eye-squared-cee". You'll use this protocol to communicate between the uC and an integrated circuit (IC) used for temperature sensing.

For this phase, you'll need a little more hardware. Specifically, you'll need a Firmware Test Board (FTB) and a click board with the TMP117 chip on it. A click board is a small board with an IC meant to 'click' into the spot on the FTB for easy testing.

To get this phase working, you will need to modify targets/phase3/main.cpp and src/dev/TMP117.cpp. The header file include/dev/TMP117.hpp has been provided for you.

At the end, you'll also need a Saleae Logic Analyzer to see the I2C waveforms. For more information on the Saleae Logic Analyzer, visit our webpage, or ask a senior member to explain.

Task Breakdown

  1. Learn about I2C through a short video (10 min) or if you have a poor attention span, a really short video (1 min).
  2. Read the I2C documentation.
  3. Read the datasheets/datasheets.md section about the TMP117 datasheet.
  4. Write the constructor and implementation for readTemp() in TMP117.cpp.
  5. Write the target code to call these functions and print temperatures over UART.
  6. Read the Saleae documentation.
  7. Use the Saleae to decode the waveforms on SDA and SCL and confirm the data matches what is output over UART.

Suggestions

  • Read the FTB documentation.
  • Set up the UART code before finishing your TMP117 implementation, so you can use the target to test.
  • Combine the two bytes you read into a single 16-bit integer.
  • Avoid floating point math, i.e. instead of 2 * .05, do (2 * 5) / 100
  • Look at the I2C sample in EVT-core for an example.

Completion

When believe you've gotten everything working, try holding your thumb against the TMP chip to heat it up. Then, blow on it to cool it down. Does the reported value update appropriately? Once you're satisfied with your code's performance, call over a senior member and show them your work. Also be sure to show them the waveform recorded by the Saleae. Once they say it looks good, you can move on to the next phase.