Nios II Assembler Editor

Use any text editor to create a file with a .s extension and feed the file to gcc - as you would with a C file.

In practise the compiler generated code won't be that much larger/slower than carefully wrtitten C, and it less likely to have obscure bugs.

You might need to understand the constraints the language puts on the compiler, and modify the C appropriately (especially if trying to get rid of pipeline stalls), but the C generated code will be more maintainable.

It can be worth looking at the generated code to check that nothing silly is happening.