this fixes an issue with DMA to SPI6 on STM32H7. On the H7 SRAM4 can
be used for DMA and BDMA to all devices except for SDMMC which uses
IDMA.
by separating out DMA of sdcard data from other data we can arrange
for DMA to all devices to work
Just setting up the periodic callback sampling time on initialization
may not work well for sensors that need to request for a sample with a
bus transaction, sleep and then read the new data. That's because the
function will be kept calling at a periodic rate, while the time in
which we can read the value is not really that sampling time, but rather
the time in which sensor was last read + the time spent in the function
before sending a new sample request.
Instead of creating a new type of thread to handle this case, just
implement the minimal and easy case of updating the period for this
callback, that can only be called from inside the callback function.
Andrew Tridgell
Hannes Verschore
Alexander Malishev
bugobliterator
Peter Barker
Lucas De Marchi