gnu as supports an additional directive to change the mips Instruction Set Architecture level on the fly: .set mipsn. n should be a number from 0 to 5, or 32, 32r2, or 64. The values other than 0 make the assembler accept instructions for the corresponding isa level, from that point on in the assembly. .set mipsn affects not only which instructions are permitted, but also how certain macros are expanded. .set mips0 restores the isa level to its original level: either the level you selected with command line options, or the default for your configuration. You can use this feature to permit specific r4000 instructions while assembling in 32 bit mode. Use this directive with care!
The directive .set mips16 puts the assembler into MIPS 16 mode, in which it will assemble instructions for the MIPS 16 processor. Use .set nomips16 to return to normal 32 bit mode.
Traditional mips assemblers do not support this directive.