Temperature Display: LED Via A PWM Controller

See also

• PWM Userspace Interface (using PCA9685)

Standup Records

2023-11-20

• Use raw file IO (see :doc: Files And File Descriptors)

• Do not do the export (making /sys/class/pwm/pwmchip0/pwm0 available to userspace) dance; rather place that responsibility on a “system-setup phase” (that we don’t have).

  “System setup” will have to be done manually before an application run. At the time that this becomes too cumbersome, define how we want it.

• Look out for something like

  class PercentageDisplay
  {
  public:
      // ...
      virtual void show_percentage(unsigned int) = 0;
      // ...
  };
  

• Refactoring round (just like (DONE) Switch Interface): put everything display-like under its hood

2023-12-14

• src_demos/? Move things to toolcase/base/!

• What’s the relationship between, e.g.

  • src_demos/LEDStripeDisplay.h and toolcase/base/display-led-stripe.h

  • src_demos/PWMDisplay.h and toolcase/base/pwm_controller.h

  ⟶ unify!

Requirements

Implement a class that implements PWM control according to PWM Userspace Interface (using PCA9685).

When done, try hard to unify (by defining an interface that both implement) that class with the LEDStripeDisplay that we have in our project. Hint: both are used to show percentages.

Implementation

See also

• PWM Userspace Interface (using PCA9685)

• Write a class PWMDisplay that has methods

  • (Constructor). Configures the PWM channel; parameters channel (int) and period (unsigned long?).

    • Export the PWM channel. Write 5 (or whatever the channel is) into /sys/class/pwm/export. Note that one has to wait a bit until the pwm5 directory becomes visible.

    • Configure the period. Write 10000000 (or whatever period was configured) into the period file.

  • void set_percentage(unsigned long percentage);

    Compute the appropriate duty cycle and write that into the duty_cycle file.

  • Use unbuffered IO, like in Files And File Descriptors, and in the exercise Exercise: Copy A File

Testing

It is hard to come up with automatic tests for real hardware. (Although the file operations could somehow be verified.)

Write a test program in bin/ that you use interactively/manually.

Future (Not Part Of This Development Cycle)

(None)