ARM: Help with instruction ADD with Operand2

Hi,

New to ARM and I don't understand why following doesn't work.

Using Cortex-M3,uVision I get the error 'Expecting constant expression'

ADD R1,R2,R3,ASR R4

All instruction references I can find give the form 'ADD Rd,Rn, <Operand2>'
and listed under 'Operand2' is 'Rm LSL Rs' so the 'ASR R4' should be legal.

Any help to clear this up would be appreciated.

Thanks