This patch implements the real time clock module for the QN908X cpus.
This module is very straightforward with only the one notable drawback
that it doesn't have a match register like the CTIMER block to implement
the alarm function. Instead, this driver can only use the interrupt
generated ever 1 second to implement the alarm match comparison in
software.
The QN908x CPU has several timer modules: one RTC (Real-Time Clock) that
can count from the 32kHz internal clock or 32.768 kHz external clock,
four CTIMER that use the APB clock and have four channels each and one
SCT timer with up to 10 channels running on the AHB clock.
This patch implements a timer driver for the CTIMER blocks only, which
is enough to make the xtimer module work. Future patches should improve
on this module to support using the RTC CNT2 32-bit free-running
counter unit and/or the SCT timer.
The QN908x has four FLEXCOMM interfaces that support a subset of UART,
SPI or I2C each one. This patch adds generic support for dealing with
the FLEXCOMM initialization and interrupts and adds a driver for
RX/TX support in UART.
With this patch is now possible to use a shell on the device over UART.
The NXP QN908x CPU family is a Cortex-M4F CPU with integrated USB,
Bluetooth Low Energy and in some variants NFC. This patch implements the
first steps for having support for this CPU.
While the QN908x can be considered the successor of similar chips from
NXP like the KW41Z when looking at the feature set, the internal
architecture, boot image format and CPU peripherals don't match those
in the Kinetis line. Therefore, this patch creates a new directory for
just the QN908x chip under cpu/qn908x.
The minimal set of peripherals are implemented in this patch to allow
the device to boot and enable a GPIO: the gpio and wdt peripheral
modules only.
The wdt driver is required to boot and disable the wdt. On reset, the
wdt is disabled by the chip, however the QN908x bootloader stored in
the internal ROM enables the wdt and sets a timer to reboot after 10
seconds, therefore it is needed to disable the wdt in RIOT OS soon
after booting. This patch sets it up such that when no periph_wdt module
is used the Watchdog is disabled, but if the periph_wdt is used it must
be configured (initialized) within the first 10 seconds.
Tests performed:
Defined a custom board for this CPU and compiled a simple application
that blinks some LEDs. Manually tested with periph_wdt and with
periph_wdt_cb as well.
