/* NXP QN908x specific information for the `periph` drivers */
/**

@defgroup    cpu_qn908x NXP QN908x
@ingroup     cpu
@brief       NXP QN908x BLE-enabled Cortex-M4F MCU specific implementation

The NXP QN908x family of chips such as the QN9080 feature a Cortex-M4F,
Bluetooth Low Energy, USB 2.0 and in some SKUs like the QN9080SIP NFC as well.
The CPU is designed to be ultra-low-power and high-performance, allowing
applications with small battery capacity. It includes an optional DC-DC and LDO,
low power sleep timers, I2C, SPI, ADC, SPIFI and several other peripherals.


@defgroup    cpu_qn908x_cpuid NXP QN908x CPUID
@ingroup     cpu_qn908x
@brief       NXP QN908x CPUID driver

No configuration is necessary. The CPUID value is based on the factory assigned
default Bluetooth address in the read-only flash section which may not be the
Bluetooth address used by the Bluetooth module if a different one was programmed
there.


@defgroup    cpu_qn908x_gpio NXP QN908x GPIO
@ingroup     cpu_qn908x
@brief       NXP QN908x GPIO driver

The GPIO driver uses the @ref GPIO_PIN(port, pin) macro to declare pins.

No configuration is necessary.


@defgroup    cpu_qn908x_i2c NXP QN908x I2C
@ingroup     cpu_qn908x
@brief       NXP QN908x I2C driver

There are several FLEXCOMM interfaces in this chip, but only two of these
support I2C (FLEXCOMM1 and FLEXCOMM2) which are mapped as I2C0 and I2C1,
respectively. A single FLEXCOMM interface can only be used for one of the I2C,
UART or SPI interfaces, so for example USART1 and I2C0 can't be used at the
same time since they are both the same FLEXCOMM1 interface.

### I2C configuration example (for periph_conf.h) ###

    static const i2c_conf_t i2c_config[] = {
        {
            .dev          = I2C0,
            .pin_scl      = GPIO_PIN(PORT_A, 6),  // or A8, A12, A20
            .pin_sda      = GPIO_PIN(PORT_A, 7),  // or A9, A13, A21
            .speed        = I2C_SPEED_FAST,
        },
        {
            .dev          = I2C1,
            .pin_scl      = GPIO_PIN(PORT_A, 2),  // or A5, A23, A27
            .pin_sda      = GPIO_PIN(PORT_A, 3),  // or A4, A22, A26
            .speed        = I2C_SPEED_FAST,
        },
    };
    #define I2C_NUMOF           ARRAY_SIZE(i2c_config)


@defgroup    cpu_qn908x_timer NXP QN908x Standard counter/timers (CTIMER)
@ingroup     cpu_qn908x
@brief       NXP QN908x timer driver

The QN908x have 4 standard counter/timers (CTIMER). These timers allow to count
clock cycles from the APB clock with a 32-bit prescaler, effectively dividing
the APB clock frequency by a configurable number up to 2^32, allowing a great
range of timer frequencies selected at runtime. Each timer has 4 independent
channels to match against which can generate an interrupt.

TODO: These CTIMERs and the SCT timers can both be used as PWM as well, with
different set of capabilities. Boards should be able to split these CTIMER and
SCT blocks between pwm and timer functions.

### Timer configuration example (for periph_conf.h) ###

    #define TIMER_NUMOF           4


@defgroup    cpu_qn908x_rtc NXP QN908x Real-Time-Clock (RTC)
@ingroup     cpu_qn908x
@brief       NXP QN908x RTC driver

The RTC block in the QN908x can be driven by the external 32.768 kHz crystal or
by the internal 32 kHz RCO oscillator clock, whichever is selected as the
`CLK_32K` clock source. The RTC has an internal "second counter" calibrated
depending on the frequency of the clock source selected at the time the RTC
clock is initialized by calling @ref rtc_init.

The RTC function in this cpu doesn't have a match against a target value to
generate an interrupt like the timer peripheral, instead, the alarm function in
the rtc.h interface is implemented by an interrupt generated every second which
checks the target value in software. Keep in mind that while the RTC can operate
while the cpu is the power-down 0 mode, using the alarm functionality during
that time means that the cpu will wake up every second for a brief moment,
potentially impacting the power consumption.

No RTC-specific configuration is necessary.


@defgroup    cpu_qn908x_uart NXP QN908x UART
@ingroup     cpu_qn908x
@brief       NXP QN908x UART driver

There are several FLEXCOMM interfaces in this chip, but only two of these
support UART (FLEXCOMM0 and FLEXCOMM1). The default UART mode is 8n1 and can
be changed with the uart_mode() function. If only RX or only TX is desired, the
other pin can be set to GPIO_UNDEF.

### UART configuration example (for periph_conf.h) ###

    static const uart_conf_t uart_config[] = {
        {
            .dev          = USART0,
            .rx_pin       = GPIO_PIN(PORT_A, 17),  // or A5
            .tx_pin       = GPIO_PIN(PORT_A, 16),  // or A4
        },
        {
            .dev          = USART1,
            .rx_pin       = GPIO_PIN(PORT_A, 9),  // or A13
            .tx_pin       = GPIO_PIN(PORT_A, 8),  // or A12
        },
    };
    #define UART_NUMOF          ARRAY_SIZE(uart_config)


@defgroup    cpu_qn908x_wdt NXP QN908x Watchdog timer (WDT)
@ingroup     cpu_qn908x
@brief       NXP QN908x Watchdog timer (WDT)

The Watchdog timer in the NXP QN908x starts disabled on reset: the clock bit
`CLK_WDT_EN` is enabled in the `CLK_EN` register on reset so the timer is
running but the interrupt and reset functions are disabled. However, after the
read-only bootloader ROM in the QN908x transfer the control flow to the user
application (the RIOT kernel) the Watchdog is enabled with a timeout of 10
seconds.

If your board does not include the `periph_wdt` module, the Watchdog will be
disabled at `cpu_init()` time and there's no configuration necessary. However,
if your board or application does include it, the Watchdog will be left
configured with the 10 second timeout set by the Bootloader and you need to
call `wdt_setup_reboot()` or `wdt_setup_reboot_with_callback()` within the first
10 seconds.

The WDT block supports different clock sources which would be configured by the
board since they depend on whether the optional crystals are populated in your
board. Nevertheless, the millisecond values passed to `wdt_setup_reboot*` are
internally converted to clock ticks using the clock configured at the time the
function was called. `wdt_setup_reboot*()` can be called multiple times to
change the WDT parameters or after changing the WDT clock source, but in any
case `wdt_start()` must be called after it to start the WDT operation.

Once the WDT triggers, it is not possible to avoid the device reboot and calling
wdt_kick() from the WDT callback (if any) or after the callback was called will
not have any effect. Note that, however, if the WDT callback returns before the
configured CONFIG_WDT_WARNING_PERIOD the CPU will continue executing the code
before the WDT interrupt occurred. If this is not desired, an infinite loop at
the end of the WDT callback, after the safety operations have been performed is
advisable.

*/