The separate Schmitt trigger bit in the configuration is dropped, as
the Schmitt trigger is only every disabled when in `GPIO_DISCONNECT`
mode. So no need to encode the same information twice.
The `gpio_state_t` is improved to be a bitmask that holds the
MODER register value and a flag indicating whether open-drain mode
should be enabled.
Finally, `GPIO_DISCONNECT` is implemented. This is done by placing the
GPIO in analog mode, which by disabling the Schmitt trigger reduces
power consumption.
This commit optimizes the `gpio_conf_t` type in the following
regards:
- The "base" `gpio_conf_t` is stripped from members that only some
platforms support, e.g. drive strength, slew rate, and disabling of
the Schmitt Trigger are no longer universally available but
platform-specific extensions
- The `gpio_conf_t` is now crammed into a bit-field that is 8 bit or
16 bit wide. This allows for storing lots of them e.g. in
`driver_foo_params_t` or `uart_conf_t` etc.
- A `union` of the `struct` with bit-field members and a `bits` is used
to allow accessing all bits in a simple C statement and to ensure
alignment for efficient handling of the type
Co-authored-by: Gunar Schorcht <gunar@schorcht.net>
