Homework: PWM Controller (2026-03-16)

Getting

• Update your fork (see Distributed git: Update Your Fork From Upstream)

• Massage googletest submodule. This has to be done only once.

  $ git submodule init
  $ git submodule update
  

Exercise (Test Driven Development - TDD)

• New exercise: /exercises/pwm/_codebergaccountname_/

  • DO NOT MODIFY anything but pwm.{h,cpp}

  • Test driven development

  $ pwd
  /home/jfasch/My-Builds/FH-STECE2024-x86_64/exercises/pwm/_codebergaccountname_
  $ ./pwm-suite._codebergaccountname_
  Running main() from /home/jfasch/My-Projects/FH-STECE2024/googletest/googletest/src/gtest_main.cc
  [==========] Running 9 tests from 1 test suite.
  [----------] Global test environment set-up.
  [----------] 9 tests from pwm_test
  [ RUN      ] pwm_test.init_ok
  /home/jfasch/My-Projects/FH-STECE2024/exercises/pwm/_codebergaccountname_/test_pwm.cpp:52: Failure
  Value of: ok
    Actual: false
  Expected: true
  
  [  FAILED  ] pwm_test.init_ok (0 ms)
  [ RUN      ] pwm_test.init_nok
  [       OK ] pwm_test.init_nok (0 ms)
  [ RUN      ] pwm_test.set_period_ok
  /home/jfasch/My-Projects/FH-STECE2024/exercises/pwm/_codebergaccountname_/test_pwm.cpp:67: Failure
  Value of: ok
    Actual: false
  Expected: true
  
  [  FAILED  ] pwm_test.set_period_ok (0 ms)
  [ RUN      ] pwm_test.set_period__no_read_permissions_on_file
  /home/jfasch/My-Projects/FH-STECE2024/exercises/pwm/_codebergaccountname_/test_pwm.cpp:88: Failure
  Value of: ok
    Actual: false
  Expected: true
  
  [  FAILED  ] pwm_test.set_period__no_read_permissions_on_file (0 ms)
  [ RUN      ] pwm_test.get_period_ok
  /home/jfasch/My-Projects/FH-STECE2024/exercises/pwm/_codebergaccountname_/test_pwm.cpp:108: Failure
  Value of: ok
    Actual: false
  Expected: true
  
  [  FAILED  ] pwm_test.get_period_ok (0 ms)
  [ RUN      ] pwm_test.set_duty_cycle_ok
  /home/jfasch/My-Projects/FH-STECE2024/exercises/pwm/_codebergaccountname_/test_pwm.cpp:124: Failure
  Value of: ok
    Actual: false
  Expected: true
  
  [  FAILED  ] pwm_test.set_duty_cycle_ok (0 ms)
  [ RUN      ] pwm_test.get_duty_cycle_ok
  /home/jfasch/My-Projects/FH-STECE2024/exercises/pwm/_codebergaccountname_/test_pwm.cpp:137: Failure
  Value of: ok
    Actual: false
  Expected: true
  
  [  FAILED  ] pwm_test.get_duty_cycle_ok (0 ms)
  [ RUN      ] pwm_test.activate_deactivate_ok
  /home/jfasch/My-Projects/FH-STECE2024/exercises/pwm/_codebergaccountname_/test_pwm.cpp:153: Failure
  Value of: ok
    Actual: false
  Expected: true
  
  [  FAILED  ] pwm_test.activate_deactivate_ok (0 ms)
  [ RUN      ] pwm_test.is_active_ok
  /home/jfasch/My-Projects/FH-STECE2024/exercises/pwm/_codebergaccountname_/test_pwm.cpp:172: Failure
  Value of: ok
    Actual: false
  Expected: true
  
  [  FAILED  ] pwm_test.is_active_ok (0 ms)
  [----------] 9 tests from pwm_test (2 ms total)
  
  [----------] Global test environment tear-down
  [==========] 9 tests from 1 test suite ran. (2 ms total)
  [  PASSED  ] 1 test.
  [  FAILED  ] 8 tests, listed below:
  [  FAILED  ] pwm_test.init_ok
  [  FAILED  ] pwm_test.set_period_ok
  [  FAILED  ] pwm_test.set_period__no_read_permissions_on_file
  [  FAILED  ] pwm_test.get_period_ok
  [  FAILED  ] pwm_test.set_duty_cycle_ok
  [  FAILED  ] pwm_test.get_duty_cycle_ok
  [  FAILED  ] pwm_test.activate_deactivate_ok
  [  FAILED  ] pwm_test.is_active_ok
  
   8 FAILED TESTS
  

• Running single tests and not all at once (handy for occasional strace debugging sessions)

  $ strace ./pwm-suite.jfasch --gtest_filter=pwm_test.set_period__no_read_permissions_on_file
  

Additional Information: PWM On Linux

• See how a PWM controller is handled on Linux: Talk to Chip Using the sysfs Interface

Additional Information: C++

bool

• bool is a dedicated type, don’t have to misfit int

std::string

See also

From std::string:

• Convenient Operators: Addition, Comparison, And Such

• Compatibility With C Strings

• Conversion To Numbers: std::sto*()

• Conversion To String: std::to_string()

• C++ strings (std::string) are convenient

• Operators (see Convenient Operators: Addition, Comparison, And Such)

• ⟶ Concatentation, assignment (see Conversion To Numbers: std::sto*() and Conversion To String: std::to_string())

• Drawback: system calls like open are defined in C ⟶ needs explicit conversion back and forth (see Compatibility With C Strings)

std::filesystem::path

See also

From std::filesystem

• Paths: Concatentation, Comparison

• PWM in sysfs uses paths heavily

• ⟶ std::filesystem::path

• Conversion to C string: path.c_str(), just like std::string