Lab 2: Basic I/O and ADC-based Readout of Temperature

ECSE444 Microprocessors

Lab 2: Basic I/O and ADC-based Readout of Temperature and Voltage
You have developed in the previous laboratory exercise a complete C/assembly code for the
STM32L4+ processor. This lab exercise will teach you to use the General-Purpose Input/Output
(GPIO) pins of the processor, as well as some of the built-in blocks that track the physical status of
the processor. There are two readily available physical parameters that the STM32L4+ processor
can read: its core temperature and its voltage.
The program that you are asked to build will allow you to switch between updating the readout of
the temperature and voltage each time the blue button is pressed on your development kit. The two
variables expressing these two physical values will be observable by means of “watched variables”
that the processor and the IDE allow you observing during the ongoing processor operation
This exercise relies on the previous laboratory exercise, all the classes and tutorials, and it will
focus on the use of basic hardware blocks within the processor. In addition to consulting the class
notes, you should consult the processor documentation to complete this exercise. Some specific
hints will be given in Tutorial 2 and the lectures leading to this lab exercise.
Background
GPIO Pins Use
You saw in the class that GPIO pins can be programmed to perform digital bit input reading, digital
pin output, various special functions, as well as the analog quantity reading/writing. You will
exercise the first two capabilities in this lab.
Output PIN – LED Driving
The simplest GPIO operation is that of outputting a zero or one, and you can test this operation by
driving the green LED light on your board. From section 6.12 of the board user manual available on
MyCourses, you will see the pin PB14 drives LED2. To drive that pin, you have to enable it in
Cube MX (started by double-clicking the .ioc file of your project) and declare as an output (by
selecting System Core-GPIO, and then the pin PB14). The tool will allow you to label this pin
with a useful mnemonic, as well as set some other parameter (e.g., pull-up or -down). Consider
carefully the suitable values for those by consulting the board schematic and the basic electric
circuits knowledge.
Input PIN – Button Readout
Similarly, you can locate the blue button pin and configure it as an input. Again, consult the circuit
schematic to deduce the default state (i.e., when button is not pressed) and the potential need for 
pull resistors to be included in the pin configuration.
Analog to Digital Converter (ADC)
STM32L4+ processors are equipped by flexible high-performance ADC converters, as described in
detail in Sec. 21.2 of the STM32L4+ Reference Manual, available on MyCourses. Commonly, an
ADC would read analog quantities via external pins, but it is simpler to first focus on reading out a)
the internal reference voltage and b) the internal temperature sensor.
The simplest way to obtain a correct value from an ADC is to start conversion and then read out the
value after the conversion is completed, and we will use this method.
Lab 2 - Exercise
You will perform this exercise in several stages and record the results obtained at each step in your
lab report.
Step 1
First, you will write a main C program that detects the pressing of the button and tests the LED2
display by toggling the value every time the button pressed. It is perfectly acceptable to have this
program run in an infinite loop generated by Cube MX after you configured the two GPIO pins.
You should take note of the commands added for initializing the GPIOs, as it illustrates a way by
which the Cube MX GUI generates correct code for your program.
Step 2
You will configure the ADC1 to read out the reference voltage and augment your code to convert
the value read to a correct voltage value. After generating the code from Cube MX, please take
notice of the control structures instantiated for ADC1 and the values generated (especially the
assignment of the reference voltage as the source for ADC conversion). You can test the obtained
values by observing that variable in your code – no need to interrupt the execution.
Step 3
Similar to Step 2, you should configure the ADC1 to read out the temperature, and then add a
correct conversion into your program variable, such that the value of that variable is the
temperature in degrees Celsius.
Step 4
This is the “detective” part of your exercise, where you will compare the code obtained in steps 2
and 3, such that your program control can switch the readouts between the voltage and the
temperature. It helps to consult the reference manual to find how to correctly initialize the readings
“on fly” to avoid the errors in the procedure.
Step 5
Produce the final program that alternates between the ADC readings and prepare it for the
demonstration to a TA. The LED light should help in understanding what the processor is doing.
Step 6 - optional
Activate interrupt generation by pressing blue button and adjust the code to perform action
associated with the button by interrupts.
Useful Notes
In realizing your code, you are free to use good C coding practices, such as the use of conditional
compiling for retargeting to different execution cases given above.
If you start your project by using the board support package (BSP) for your board, the clock and
pins will be properly selected for you. It is a good practice to check the clock and
The Debugger
While developing your code, you will spend substantial time using the debugger. Please follow the
instruction from your tutorials to ensure proper development and debug practices.
Experimental Results to Report
You are asked to reach the following milestones and include the results in your report.
1. Describe the configuration of pins such that the Step 1 is correctly run on the processor,
2. Describe the ADC1 configuration for Step 2,
3. Describe the ADC1 configuration for Step 3,
4. Document the code for programmable reconfiguration of ADC1.
5. Readable and concise code/pseudo-code for your final program execution
6. Test the temperature sensor readings by (non-destructive!) heating and cooling of the
processor. Fingers pressed on the processor can raise temperature a bit, and natural
convection will reduce it. You can also consider the use of a hair fan.
Final Report
Once you have all the parts working, include all the relevant data to your report, which will be due
first day in a week following the Lab 2 demonstration, but not later than 4 days after the demo.
Demonstration
The demonstration includes showing your source code and demonstrating a working program.
Your program should be capable of manipulating a variety of test cases and should flag errors
appropriately.
Report
The report should concisely explain your solution to the problem given, including the final code.
All code should be well documented. Your report should contain a performance evaluation and
correctness validation. More detail on the report will be given out in the class.
Due Dates
The first two labs will be completed in several phases, over the three weeks. First, you should take
time to understand the lab and ask any questions in regular lab sessions or through discussion
groups.
There will be the first lab demonstration on
Feb. 16-18th
,
by which time you should be able to explain to the TAs how you approach the exercise.
The final demonstration in which the parts are put together and run on test cases will be on
Feb. 23th and 25th
and will include showing your source code and demonstrating a working program for all test cases
that we will post.
The final report will be due on
Friday, Feb. 26th.