Merge request https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/1499 
was reviewed by Christian Mauderer

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Christian Mauderer commented on a discussion on cpukit/include/dev/gpio/gpio.h: 
https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/1499#note_159746

 > + * @retval -1 An error occurred.  The errno is set to indicate the error.
 > + */
 > +int rtems_gpio_pin_irq_enable(int fd, uint32_t pin,

What I meant is more or less: Do we need something like the 
`RTEMS_INTERRUPT_SHARED` flag of the `rtems_interrupt_handler_install`? Use 
case would be that you can create a shared interrupt line with that. For 
example, you can add three SPI-UART chips to one interrupt line with a 
hardware-OR-construction. If you have that, it's much simpler for the UART 
driver if it can simply install three interrupt handlers to one interrupt pin.

--
  
Christian Mauderer commented on a discussion on cpukit/include/dev/gpio/gpio.h: 
https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/1499#note_159747

 > +   */
 > +  RTEMS_GPIO_DIRECTION_OUTPUT
 > +} rtems_gpio_direction;

For energy saving reasons, it can often be useful to set all unused pins into a 
low power mode. If the manufacturer doesn't have any specific requirements, 
that usually means to just make sure that the pin doesn't float. Otherwise, the 
input gates toggle all the time from random noise and need a bit of energy each 
time they toggle.

For most controllers that just means that you set the pin to a driven output or 
an input with pull-up or down. But I have seen a controller (I think a small 
Kinetis) where the manufacturer said that there is a special "analog" state for 
the pins where they are disconnected. So you had to actively initialize the pin 
to that state to save energy.


-- 
View it on GitLab: 
https://gitlab.rtems.org/rtems/rtos/rtems/-/merge_requests/1499
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