Block write and block read performance

[m-kru]

Block write (bwrite) and block read (bread) must be part of the interface. They might not be supported by the hardware if the maximum throughput is not needed. In such a case, the software implementation of bwrite/bread is simply an iterative call to the write/read.

To make deterministic and manageable solution the performance of bwrite/bread must be known compared to the write/read. The back-end makes call to the bwrite/bread whenever it needs an access to the consecutive registers starting from two registers. This implies, that single bwrite/bread must have at least the same performance as two writes/reads. If this condition is not met, everything will still work correctly, however the achieved performance will be worse. This soft requirement ease the implementation as the threshold when calling bwrite/bread makes sense is fixed, and there is no need to pass this extra information to the back-end when performance is crucial.