The calculation of `_state_index` is broken for `port = 2`
_gpio_isr_map[n + (port<<1)];
Will not yield the right result. As a consequence, IRQs on Port 2
are not working.
The right thing here would be
_gpio_isr_map[n + (port ? 32 : 0)];
But we might just re-using the `_isr_map_entry()` function.
Also only iterate as many times as there are set interrupt bits.
- Fixed documentation
- Use bitwise operation instead of multiplication and addition in `GPIO_PIN()`
- Allow GPIOs to be configured as input via `gpio_init()`
- Fixed bugs in `gpio_init_mux`:
- `0x01 << ((pin & 31) * 2)` was used before to generate the bitmask, but
this would shift by 62 to the left. Correct is `0x01 << ((pin & 15) * 2)`
(See [datasheet](https://www.nxp.com/docs/en/user-guide/UM10211.pdf) at
pages 156ff)
- Only one of the two bits was cleared previously
- Changed strategy to access GPIO pins:
- Previous strategy:
- Set all bits in FIOMASK except the one for the pin to control to
disable access to them
- Set/clear/read all pins in the target GPIO port (but access to all but
the target pin is ignored because of the applied FIOMASK)
- New strategy:
- Set/clear/read only the target pin
- Advantages:
- Only one access to a GPIO register instead of two
- Proven approach: Access to GPIOs on lpc2387 is mostly done by
accessing the GPIO registers directy (e.g. see the sht11 driver).
Those accesses never touch the FIOMASK register
- No unwanted side effects: Disabling all but one pin in a GPIO port
without undoing that seems not to be a good idea
