Posted on November 16, 2017 at 03:15GCC can independently use the built-in DSP functions. But for this it is necessary to write the code explicitly. Instead of writing the names of variables in the explicit simple form a + = b * c, it is necessary to use their addresses. Approximately so a [x] + = b [x] * c [x]. The operation must be cyclic - to exclude optimization by the GCC. Otherwise, it loads the values of the variables into registers, and performs separate operations - it's so much easier for him.
Almost all DSP functions work with indirect addressing, in the sense that an address is used to load data - but not the data already in the registers. This must be taken into account.
The use of fractional numbers is a misunderstanding. GCC does not know how to work with types q15_t in automatic mode, it does not even understand what it is. Therefore, all operations with such numbers must be performed through built-in libraries. That does not always give a benefit in speed and quality.
A good result can be achieved in the case of self-assembly algorithm, it is almost always a pure assembler.
