Setting up a DMA transfer can take longer than sending out a buffer
byte by byte if the buffer is small.
DMA only shows advantages for large buffers, using it for every transfer
will cause a net slowdown.
Since we did not come up with a good way to determine the treshold based
on the SPI frequency, just use a fixed buffer for now so that DMA can be
used without slowing things down overall.
`pm_set()` gets called by the idle thread whose stack is too small
for normal DEBUG()/printf().
Use DEBUG_PUTS() instead to print the static debug strings.
The currently supported SAM0 MCUs (samd21, saml21, saml1x) share the same
Timer peripheral, yet each of them carries it's own copy of the Timer
driver.
This introduces a new timer driver that is common for all sam0 MCUs and
uses structs for configuration instead of defines.
The currently supported SAM0 MCUs (samd21, saml21, saml1x) share the
same RTC peripheral, yet each of them carries it's own copy of the RTT
driver.
Unify the drivers and move them to sam0_common.
The currently supported SAM0 MCUs (samd21, saml21, saml1x) share the
same RTC peripheral, yet each of them carries it's own copy of the RTC
driver.
Unify the drivers and move them to sam0_common.
