The new syntax requires that VU0 register names be prefixed with a '$' symbol and only single digit numerals be used for registers 0 through 9.
Numerical register names are to be used for the transfer instructions lqc2/sqc2/ctc2/cfc2/qmtc2/qmfc2.
The "vcallms" instruction only takes immediate expressions, now. The assembler divides the value given by 8 implicitly.
The "vcallmsr" instruction takes no arguments now. It didn't need the "vi27" operand, since it was set as part of the instruction. I don't think it was possible to change the register number.
This option enables support for legacy VU0 register name syntax.
The '$' symbol becomes optional.
Double digits can be used for registers 0 through 9.
VU0 register names can be used for transfer instructions.
This option enables integer and floating point register names to be used interchangeably for the ctc2/cfc2/qmtc2/qmfc2 instructions. Make sure to keep track.
This forces the assembler to output a hardware "ld/sd" instruction regardless of ABI/ISA. This simulates the prior behavior of the r5900 toolchain, but should only be used for debugging purposes.