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Author SHA1 Message Date
Lucas De Marchi 61ef653181 AP_HAL_Linux: implement SPIDevice
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.
2016-02-16 19:49:09 -02:00