Why does ARMSim# not recognize instruction 'addw'?

For the below code, ARMSim# does not recognize '.arch armv7-r'. It says:
"unknown opcode or directive: .arch"It does not recognize 'addw' either, says:
"unknown opcode or directive: addw"I have check ARMTRM. 'addw' is a legal assembly code.
'.arch' is also used in some assembler.
How do you think ARMSim# want?
Thanks.
////////////////////
.arch armv7-r
.syntax unified
.text
.thumb
        .global foo
foo:        
@ Section A6.1.3 "Use of 0b1101 as a register specifier".@ R13 as the source or destination register of a mov instruction.
@ only register to register transfers without shifts are supported,
@ with no flag settingmov        sp,r0
mov        r0,sp@ Using the following instructions to adjust r13 up or down by a
@ multiple of 4:add        sp,sp,#0
addw        sp,sp,#0