Device Drivers external from Zephyr: Need to add access to the GPIO pins and other resources?

[KurtE]

Suppose one wishes to write a driver, that is external to the Zephyr "Bootloader" code.
How does one do that?

One solution is to build every possible driver into the Zephyr build, however I don't think they would all fit and if
they did probably would not leave very many resources left for an application. And it would probably not work,
as for example on A portenta H7, you might use any of the current carrier boards/shields and they probably cause conflicts between all such devices.

With the GIGA we currently have most all of the GPIO pins exported. But for example if one looks to maybe port something from MBED, like maybe the ArduCam library. They are addressed using pin names like:
#define DCMI_RESET_PIN (PA_1)
But this at least can currently be addressed by using pin 66...

But currently on the Portenta H7: it wants to use PE_3 which is not included in the current pin table,
which only includes the GPIO pins on the exterior of the H7, and not any of them on the high density
connectors on the bottom of the board (unless of course if they are one of the one on the exterior of the board).

Personally I believe the pin names such as used in the MBED version should be defined and/or those for example
that are defined as part of Micropython, such as shown in the page:
https://docs.arduino.cc/tutorials/portenta-h7/openmv-cheat-sheet/

Should be defined.

For now I will setup and hack up my own implementation. I currently have done that a few times with
Zephyr direct test apps, although to make it easier I modified the device tree overlay. But I am hoping
that we don't have to do that in the future...

[mjs513]

For now I will setup and hack up my own implementation. I currently have done that a few times with
Zephyr direct test apps, although to make it easier I modified the device tree overlay. But I am hoping
that we don't have to do that in the future...

I remember doing this a while back and it worked quite well.

[KurtE]

@mjs513 @pillo79 I am thinking the only way here to make progress on this, and get feedback and maybe something implemented and pulled in, is to create another PR, like the ones I did earlier with different options and see if anything gets
any traction.

Option 1, bypasses Zephyr, manipulate the GPIO registers directly...

Option 2, Have a complete list of all possible pins. Either extend current ones at end with all of them or have secondary list.
On some of my test apps, I do the following:
Add complete list, to device tree:

	zephyr,user {
		all-pin-gpios = 
					<&gpioa 0 0>, <&gpioa 1 0>, <&gpioa 2 0>, <&gpioa 3 0>, <&gpioa 4 0>, <&gpioa 5 0>, <&gpioa 6 0>, <&gpioa 7 0>,
				    <&gpioa 8 0>, <&gpioa 9 0>, <&gpioa 10 0>, <&gpioa 11 0>, <&gpioa 12 0>, <&gpioa 13 0>, <&gpioa 14 0>, <&gpioa 15 0>,
					<&gpiob 0 0>, <&gpiob 1 0>, <&gpiob 2 0>, <&gpiob 3 0>, <&gpiob 4 0>, <&gpiob 5 0>, <&gpiob 6 0>, <&gpiob 7 0>,
				    <&gpiob 8 0>, <&gpiob 9 0>, <&gpiob 10 0>, <&gpiob 11 0>, <&gpiob 12 0>, <&gpiob 13 0>, <&gpiob 14 0>, <&gpiob 15 0>,
					<&gpioc 0 0>, <&gpioc 1 0>, <&gpioc 2 0>, <&gpioc 3 0>, <&gpioc 4 0>, <&gpioc 5 0>, <&gpioc 6 0>, <&gpioc 7 0>,
				    <&gpioc 8 0>, <&gpioc 9 0>, <&gpioc 10 0>, <&gpioc 11 0>, <&gpioc 12 0>, <&gpioc 13 0>, <&gpioc 14 0>, <&gpioc 15 0>,
					<&gpiod 0 0>, <&gpiod 1 0>, <&gpiod 2 0>, <&gpiod 3 0>, <&gpiod 4 0>, <&gpiod 5 0>, <&gpiod 6 0>, <&gpiod 7 0>,
				    <&gpiod 8 0>, <&gpiod 9 0>, <&gpiod 10 0>, <&gpiod 11 0>, <&gpiod 12 0>, <&gpiod 13 0>, <&gpiod 14 0>, <&gpiod 15 0>,
					<&gpioe 0 0>, <&gpioe 1 0>, <&gpioe 2 0>, <&gpioe 3 0>, <&gpioe 4 0>, <&gpioe 5 0>, <&gpioe 6 0>, <&gpioe 7 0>,
				    <&gpioe 8 0>, <&gpioe 9 0>, <&gpioe 10 0>, <&gpioe 11 0>, <&gpioe 12 0>, <&gpioe 13 0>, <&gpioe 14 0>, <&gpioe 15 0>,
					<&gpioe 0 0>, <&gpioe 1 0>, <&gpioe 2 0>, <&gpioe 3 0>, <&gpioe 4 0>, <&gpioe 5 0>, <&gpioe 6 0>, <&gpioe 7 0>,
				    <&gpioe 8 0>, <&gpioe 9 0>, <&gpioe 10 0>, <&gpioe 11 0>, <&gpioe 12 0>, <&gpioe 13 0>, <&gpioe 14 0>, <&gpioe 15 0>,
					<&gpiof 0 0>, <&gpiof 1 0>, <&gpiof 2 0>, <&gpiof 3 0>, <&gpiof 4 0>, <&gpiof 5 0>, <&gpiof 6 0>, <&gpiof 7 0>,
				    <&gpiof 8 0>, <&gpiof 9 0>, <&gpiof 10 0>, <&gpiof 11 0>, <&gpiof 12 0>, <&gpiof 13 0>, <&gpiof 14 0>, <&gpiof 15 0>,
					<&gpiog 0 0>, <&gpiog 1 0>, <&gpiog 2 0>, <&gpiog 3 0>, <&gpiog 4 0>, <&gpiog 5 0>, <&gpiog 6 0>, <&gpiog 7 0>,
				    <&gpiog 8 0>, <&gpiog 9 0>, <&gpiog 10 0>, <&gpiog 11 0>, <&gpiog 12 0>, <&gpiog 13 0>, <&gpiog 14 0>, <&gpiog 15 0>,
					<&gpiog 0 0>, <&gpiog 1 0>, <&gpiog 2 0>, <&gpiog 3 0>, <&gpiog 4 0>, <&gpiog 5 0>, <&gpiog 6 0>, <&gpiog 7 0>,
				    <&gpiog 8 0>, <&gpiog 9 0>, <&gpiog 10 0>, <&gpiog 11 0>, <&gpiog 12 0>, <&gpiog 13 0>, <&gpiog 14 0>, <&gpiog 15 0>,
					<&gpioh 0 0>, <&gpioh 1 0>, <&gpioh 2 0>, <&gpioh 3 0>, <&gpioh 4 0>, <&gpioh 5 0>, <&gpioh 6 0>, <&gpioh 7 0>,
				    <&gpioh 8 0>, <&gpioh 9 0>, <&gpioh 10 0>, <&gpioh 11 0>, <&gpioh 12 0>, <&gpioh 13 0>, <&gpioh 14 0>, <&gpioh 15 0>,
					<&gpioi 0 0>, <&gpioi 1 0>, <&gpioi 2 0>, <&gpioi 3 0>, <&gpioi 4 0>, <&gpioi 5 0>, <&gpioi 6 0>, <&gpioi 7 0>,
				    <&gpioi 8 0>, <&gpioi 9 0>, <&gpioi 10 0>, <&gpioi 11 0>, <&gpioi 12 0>, <&gpioi 13 0>, <&gpioi 14 0>, <&gpioi 15 0>,
					<&gpioj 0 0>, <&gpioj 1 0>, <&gpioj 2 0>, <&gpioj 3 0>, <&gpioj 4 0>, <&gpioj 5 0>, <&gpioj 6 0>, <&gpioj 7 0>,
				    <&gpioj 8 0>, <&gpioj 9 0>, <&gpioj 10 0>, <&gpioj 11 0>, <&gpioj 12 0>, <&gpioj 13 0>, <&gpioj 14 0>, <&gpioj 15 0>,
					<&gpiok 0 0>, <&gpiok 1 0>, <&gpiok 2 0>, <&gpiok 3 0>, <&gpiok 4 0>, <&gpiok 5 0>, <&gpiok 6 0>, <&gpiok 7 0>;

	};

Code side I have:

extern "C" {

static const struct gpio_dt_spec pin_name_pins[] = {DT_FOREACH_PROP_ELEM_SEP(
    DT_PATH(zephyr_user), all_pin_gpios, GPIO_DT_SPEC_GET_BY_IDX, (, ))};

// clang-format off
typedef enum {
  PA_0, PA_1, PA_2, PA_3, PA_4, PA_5, PA_6, PA_7,
  PA_8, PA_9, PA_10, PA_11, PA_12, PA_13, PA_14, PA_15,
  PB_0, PB_1, PB_2, PB_3, PB_4, PB_5, PB_6, PB_7,
  PB_8, PB_9, PB_10, PB_11, PB_12, PB_13, PB_14, PB_15,
  PC_0, PC_1, PC_2, PC_3, PC_4, PC_5, PC_6, PC_7,
  PC_8, PC_9, PC_10, PC_11, PC_12, PC_13, PC_14, PC_15,


  PD_0, PD_1, PD_2, PD_3, PD_4, PD_5, PD_6, PD_7,
  PD_8, PD_9, PD_10, PD_11, PD_12, PD_13, PD_14, PD_15,
  PE_0, PE_1, PE_2, PE_3, PE_4, PE_5, PE_6, PE_7,
  PE_8, PE_9, PE_10, PE_11, PE_12, PE_13, PE_14, PE_15,
  PF_0, PF_1, PF_2, PF_3, PF_4, PF_5, PF_6, PF_7,
  PF_8, PF_9, PF_10, PF_11, PF_12, PF_13, PF_14, PF_15,
  PG_0, PG_1, PG_2, PG_3, PG_4, PG_5, PG_6, PG_7,
  PG_8, PG_9, PG_10, PG_11, PG_12, PG_13, PG_14, PG_15,
  PH_0, PH_1, PH_2, PH_3, PH_4, PH_5, PH_6, PH_7,
  PH_8, PH_9, PH_10, PH_11, PH_12, PH_13, PH_14, PH_15,
  PI_0, PI_1, PI_2, PI_3, PI_4, PI_5, PI_6, PI_7,
  PI_8, PI_9, PI_10, PI_11, PI_12, PI_13, PI_14, PI_15,
  PJ_0, PJ_1, PJ_2, PJ_3, PJ_4, PJ_5, PJ_6, PJ_7,
  PJ_8, PJ_9, PJ_10, PJ_11, PJ_12, PJ_13, PJ_14, PJ_15,
  PK_0, PK_1, PK_2, PK_3, PK_4, PK_5, PK_6, PK_7
} PinNames;
// clang-format on

typedef enum {
  LOW = 0,
  HIGH = 1,
  CHANGE = 2,
  FALLING = 3,
  RISING = 4,
} PinStatus;

typedef enum {
  INPUT = 0x0,
  OUTPUT = 0x1,
  INPUT_PULLUP = 0x2,
  INPUT_PULLDOWN = 0x3,
  OUTPUT_OPENDRAIN = 0x4,
} PinMode;

void pinMode(PinNames pinNumber, PinMode pinMode) {
  if (pinMode == INPUT) { // input mode
    gpio_pin_configure_dt(&pin_name_pins[pinNumber],
                          GPIO_INPUT | GPIO_ACTIVE_HIGH);
  } else if (pinMode == INPUT_PULLUP) { // input with internal pull-up
    gpio_pin_configure_dt(&pin_name_pins[pinNumber],
                          GPIO_INPUT | GPIO_PULL_UP | GPIO_ACTIVE_HIGH);
  } else if (pinMode == INPUT_PULLDOWN) { // input with internal pull-down
    gpio_pin_configure_dt(&pin_name_pins[pinNumber],
                          GPIO_INPUT | GPIO_PULL_DOWN | GPIO_ACTIVE_HIGH);
  } else if (pinMode == OUTPUT) { // output mode
    gpio_pin_configure_dt(&pin_name_pins[pinNumber],
                          GPIO_OUTPUT_LOW | GPIO_ACTIVE_HIGH);
  }
}

void digitalWrite(PinNames pinNumber, PinStatus status) {
  gpio_pin_set_dt(&pin_name_pins[pinNumber], status);
}

PinStatus digitalRead(PinNames pinNumber) {
  return (gpio_pin_get_dt(&pin_name_pins[pinNumber]) == 1) ? HIGH : LOW;
}

} // extern "C"

And calling code, looks like:

  // quick hack
  printk("Before manual setting RESET PWDN");
  pinMode(PE_3, OUTPUT); // reset
  digitalWrite(PE_3, HIGH);
  pinMode(PD_4, OUTPUT); //pwndn
  digitalWrite(PD_4, LOW); 

Option 3:
Similar to 2, but short list, just 1 for each GPIO...

		port-pin-gpios =	<&gpioa 0 0>,
					<&gpiob 0 0>,
					<&gpioc 0 0>,
					<&gpiod 0 0>,
					<&gpioe 0 0>,
					<&gpiof 0 0>,
					<&gpiog 0 0>,
					<&gpioh 0 0>,
					<&gpioi 0 0>,
					<&gpioj 0 0>,
					<&gpiok 0 0>;

The PinNames enum is more or less the same. Since every GPIO object except last one has 16 logical pads.
Except in the implementation I was playing with there were some added for the special pins in H7...

    PA_0C      = 0X00 | DUAL_PAD,
    PA_1C      = 0X01 | DUAL_PAD,
    PC_2C      = 0X02 | DUAL_PAD,
    PC_3C      = 0X03 | DUAL_PAD,

So the implementations for the functions translates to something like:

void digitalWrite(PinName pinNumber, PinStatus status) {
  if (pinNumber & DUAL_PAD) return;
  gpio_pin_set(arduino_ports[pinNumber >> 4].port, pinNumber & 0xf, status);
}

PinStatus digitalRead(PinName pinNumber) {
  if (pinNumber & DUAL_PAD) return LOW;
  return (gpio_pin_get(arduino_ports[pinNumber >> 4].port, pinNumber & 0xf) == 1) ? HIGH : LOW;
}

Can show the rest if interested....