Special Characters
A register name can optionally be prefixed by a ‘ % ’ character. So register %r0 is equivalent to r0 in the assembly code.
The presence of a ‘ # ’ character within a line (but not at the start of a line) indicates the start of a comment that extends to the end of the current line.

Note: if a line starts with a ‘ # ’ character then it can also be a logical line number directive (see Comments ) or a preprocessor control command (see Preprocessing ).

Prefixing an operand with an ‘ @ ’ specifies that the operand is a symbol and not a register. This is how the assembler disambiguates the use of an ARC register name as a symbol. So the instruction
          mov r0, @r0

moves the address of symbol r0 into register r0 .

The ‘ ` ’ (backtick) character is used to separate statements on a single line.

Used as a separator to obtain a sequence of commands from a C preprocessor macro.