Exercise: Reading A Sensor (Driven By Tests)

Setup

Clone, setup, and build https://github.com/jfasch/FH-STECE2022 (see instructions on the project page)

exercises/02-sensor: Exercise Structure

In exercises/02-sensor there exist the following directories,

  • bin/ has read-sensor.c - the main program (see below)

  • lib/ has the library - the sensor implementation

  • tests/ has the unit tests that define the sensor functionality

We start by running the tests - these remain unchanged, and fixing lib/sensor.c until all tests are green. Only then we implement bin/read-sensor.c.

tests/suite-sensor.cpp: Unit Tests (Requirements Definition)

In the tests/ directory,

$ pwd                           # <--- build directory
/home/jfasch/My-Builds/FH-STECE2022-x86_64
$ ./exercises/02-sensor/tests/02-sensor-tests
... OMG: all tests fail! ...

Now we can start to fix lib/sensor.c until the tests are green.

lib/sensor.c: Sensor Implementation

Fix until tests are green.

Hints

  • The relevant errno values are

    • ENOENT

    • EACCES

  • See man -s 3 sscanf for string to integer conversion.

  • Use the valgrind (The Valgrind Quick Start Guide) tool to check for errors.

    $ valgrind --track-fds=yes ./exercises/02-sensor/tests/02-sensor-tests
... leaks ...

  • Especially, try hard to close the file descriptor in any case.

bin/read-sensor.c: Sensor Reading Program (But Wait!)

The final goal is to have a program that can read a sensor value. In fact, it is supposed to read a file like /sys/bus/w1/devices/28-02131d959eaa/temperature that contains the temperature in milli degrees Celsius.

$ cat /sys/bus/w1/devices/28-02131d959eaa/temperature
21340
$ ./exercises/02-sensor/bin/read-sensor /sys/bus/w1/devices/28-02131d959eaa/temperature
21.34

But lets not use hardware until we go into the integration test phase. We can just as well read an ordinary file instead,

$ echo 21340 > /tmp/temperature
$ ./exercises/02-sensor/bin/read-sensor /tmp/temperature
21.34

That program should read the sensor file, and output the temperature in a floating point format, representing degrees in Celsius.

The program should not open and the file in its main() function, but rather use a function read_temperature() that we define in the next step.

Submission

The entire project source is submitted. You have a FH-STECE2022/ directory somewhere which is the cloned project’s root, and this is what’s in the submitted tar file.

$ tar -J -c -f submission.tar.xz FH-STECE2022/

  • Submit submission.tar.xz

Attention

  • Build outside the source tree!

  • Only source code is submitted!