If a write to a full tsrb is attempted with disabled interrupts
or in a interrupt then a deadlock will occure. To avoid this make
space in the ringbuffer by synchrnously writing to uart.
The DMA stream will automatically disable itself as soon as the transfer
is finished. No need to do this an additional time after the transfer is
finished
This combines a number of register writes in the SPI
acquire and transfer code. The DMA enable for SPI is moved to the
acquire function, switching between DMA and regular transfer between
acquires is not possible.
This commit adds two new functions to the DMA peripheral code for the
stm32. The setup function allows for a one-time setup of peripheral
config. The prepare function does the per-transfer setup. This allows
for a single setup call during the peripheral lock step and a
per-transfer call to the prepare function.
This commit removes a number of assert statements that should already
have been hit before. This is the reason that the assert in the
acquire function is left.
The FCR register content might change during mem-to-mem DMA transfers,
Forcing it back in the acquire should be sufficient to ensure proper
operations.
