HLAs have no way of knowing what 'transaction' the bytes belong to; they simply receive a continuous stream of bytes with no separation based on CS/Enable. It would be great if the SPI result included a 'transaction' field that was an integer that incremented every time the CS/Enable line is deasserted/reasserted.
Ideally it would also be possible for an HLA to know when the CS/Enable line has been deasserted, even when no more bytes have been transferred. Without this it is not possible to 'terminate' the parsing of a frame that ends with the deassertion of CS/Enable.
Good point, we'll improve the API in a few weeks, and we'll take that into account