I am a audio expert with good knowledge in addembly.
I am using to assemnly in ARM/BlueCoreKalimba and also Simd.
Just tone generation , I am not sure why u need assembly , since C should be pretty good speed , unless your platform doesn't have a C compiler. I have a ARM platform ready for dev..but dont have another platform at hand.
What is ur platform? Do you have a documentation on the project.