The 10 bit DAC on the lpc23xx is very simple.
It only has one channel and can only be mapped to a single pin (P0.26).
After setting the pin mode to DAC no further configuration in needed.
Enable IDLE and Deep Powerdown mode.
IDLE is pretty straightforward - insteady of busy waiting, the CPU will
enter an idle state from which it will resume on any event.
Deep Power Down shuts off the entite system except for the battery backup
power domain.
That means the CPU will reset on resume and can be woken by e.g. RTC.
SLEEP and POWERDOWN disable the PLL and the PLL and Flash respectively.
This requires some proper wake-up handling.
Since this turned out to be a major time sink and those modes are never
currently never used in RIOT outside of tests, I left this as an exercise
for a future reader.
This converts the hard-coded UART driver to the new ways.
- allow the board to configure the RX & TX pins
- allow for more than one UART
- allow setting the baudrate
- implement poweron()/poweroff() functions
- 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
