The way this code is structured is a little bit different from the
SPIDriver implementation:
- We only open the bus once, no matter how many devices we have in it
- There's a single transfer() method which uses half-duplex mode
instead of full duplex. The reason is that for all cases in the
codebase we are using half-duplex transfers using the full-duplex
API, i.e. a single SPI msg with both tx and rx buffers. This is
cumbersome because the buffers need to be of the same size and the
receive buffer using an offset of the same length as the actux data
being written. This means the high level APIs need to copy buffers
around.
If later we have uses for a real full duplex case it's just a matter
of adding another transfer_fullduplex() method or something like
this.
- The methods are implemented in the SPIDevice class instead of having
proxy methods to SPIDeviceManager as is the case of SPIDriver
Also from now on we refer to the SPIDriver objects as "descriptors"
because they have the parameters of each device in the
SPIDeviceManager::devices[] table. When SPIDeviceDriver is completely
replaced we can rename them to SPIDeviceProperties.
Lucas De Marchi