OO Digital Pin class: single class or separate in and out classes

Andrew J said:

On the basis of your points above, what you are essentially describing is a variable: you can set a value and you can read a value.  I don't think that would benefit from being encapsulated by a class and methods

I'm not trying to encapsulate a variable. I'm trying to make GPIO pins act as if they are a variable.

You can set state by setting the value:

drive LED pin high:

led = true;

You can get current state (both out and in), by reading the value:

read LED or button pin:

state = led;

state = button;

led != led; // toggle led

led = button; // adapt led to the state of the button

While they act as variables, in the background they call the microcontroller APIs and write / read different registers.

Examples of the implementation of the "set" and "get":

IO &IO::operator= (bool high) {
	R_GPIO_PinWrite(this->pin, (gpio_level_t)high);
	return *this;
}

IO &IO::operator!= (IO &rhs) {
	R_GPIO_PinWrite(this->pin, (gpio_level_t)!((bool)rhs));
	return *this;
}

IO::operator bool() const {
	gpio_level_t l = R_GPIO_PinRead(this->pin);
	return (bool) l;
}

In essence, I abstracted gpio pins, that are controlled via several registers, into a single boolean "variable".

Andrew J said:

On the basis of your points above, what you are essentially describing is a variable: you can set a value and you can read a value.  I don't think that would benefit from being encapsulated by a class and methods

I'm not trying to encapsulate a variable. I'm trying to make GPIO pins act as if they are a variable.

You can set state by setting the value:

drive LED pin high:

led = true;

You can get current state (both out and in), by reading the value:

read LED or button pin:

state = led;

state = button;

led != led; // toggle led

led = button; // adapt led to the state of the button

While they act as variables, in the background they call the microcontroller APIs and write / read different registers.

Examples of the implementation of the "set" and "get":

IO &IO::operator= (bool high) {
	R_GPIO_PinWrite(this->pin, (gpio_level_t)high);
	return *this;
}

IO &IO::operator!= (IO &rhs) {
	R_GPIO_PinWrite(this->pin, (gpio_level_t)!((bool)rhs));
	return *this;
}

IO::operator bool() const {
	gpio_level_t l = R_GPIO_PinRead(this->pin);
	return (bool) l;
}

In essence, I abstracted gpio pins, that are controlled via several registers, into a single boolean "variable".

So you are doing more than just setting and reading values!  Clever way of doing it - I'm just not that good with C++.  Out of curiosity, how do the examples look without this C++ class?

Hi Andrew,

Quite a lot of microcontrollers have got complicated registers just to do a port action. I've not looked at the Renesas RX microcontroller that Jan is using, but for the Renesas RA microcontrollers, it uses 32-bit registers where each output is controlled by two bits, in the lower and the upper 16-bits, depending on if the desire is to set the output high or low (this is so that with the two bits there is effectively a mask capability, so that outputs that are not desired to be controlled can remain in a state without needing to first read the register and then ORing or ANDing, i.e. it's faster since no extra read is needed, nor any local variable storing the entire port state). Also with RA, completely separate registers are used for read operations.

Regarding reading output ports, it was valid in some older microcontrollers, e.g. 8051 had an system which was quite neat in some ways; some ports had pull-ups (like I2C) that could be enabled, but a read would show the physical signal level on the pin, i.e. if an external circuit was pulling the output low. I can't recall if it was allowed to be used like that or not, it's been ages since I've used it!, but it was nice that everything was easy to do with very few register operations.

Andrew J said:

Out of curiosity, how do the examples look without this C++ class?

example using Renesas register / bit mapping

#define R_LED1_On() (PORTH.PODR.BIT.B2 = 0)

#define R_LED1_Off() (PORTH.PODR.BIT.B2 = 1)

Example with their HAL API:

R_GPIO_PinWrite(GPIO_PORT_H_PIN_2, state ? GPIO_LEVEL_HIGH : GPIO_LEVEL_LOW);