raiden00pl commented on pull request #1788:
URL: https://github.com/apache/incubator-nuttx/pull/1788#issuecomment-692935987
> But that's not really documented is it? Sounds more like a side-effect.
Yes, this is just side-effect, that sets up the first GPIO to reset state.
I think now there is a more proper way to disconnect peripheral from pin -
you just define pin as in the reset state, eg
`#define GPIO_SPI1_SCK (GPIO_INPUT|GPIO_PORTA|GPIO_PIN5) // no alternate
function configured`
But this can't be done this way for NRF52, there must be a special flag in
pincfg to avoid PSEL configuration.
So maybe in other arch there is no GPIO_DISABLED flag because it is not
required there to achieve the given functionality.
> But besides the pinmux (which would be simply predefined _1, _2 values for
a given pin), pins are always mapped at buid-time with macros. It is not
necessary to define all possible values for nRF52, the macros allow a
peripheral to know what pin to use, not the other way around. So you don't need
all possible peripheral cases for a pin.
All supported NRF52 peripherals that use GPIO require logic like this to
configure PSEL
```
/* Setect TX pins for UART */
pin = GPIO_PIN_DECODE(config->txpin);
port = GPIO_PORT_DECODE(config->txpin);
regval = (pin << UART_PSELTXD_PIN_SHIFT);
regval |= (port << UART_PSELTXD_PORT_SHIFT);
putreg32(regval, base + NRF52_UART_PSELTXD_OFFSET);
```
so this is done at runtime.
I don't quite understand where this PR introduce more runtime GPIO
configuration than it is already done in code.
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