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Re: ARM SWI

From: Nick Clifton <nickc at redhat dot com>
To: Vijay Deep <vijaykpk at gwu dot edu>
Cc: newlib at sources dot redhat dot com
Date: Fri, 31 Dec 2004 13:31:36 +0000
Subject: Re: ARM SWI
References: <Pine.GSO.4.33.0412281408210.10812-100000@acad1>

Hi Vijay,

	Can anyone tell what does %1, %2, %a3 mean in the following line
"mov r0, %1; mov r1, %2; swi %a3; mov %0, r0".

This is GCC's extended asm syntax. Please check the GCC manual for more information.

%1 means "substitute the second argument here". In this case that would be the register containing the variable "reason".

%2 means "subsititute the third argument here". So this would be the register containing the variable "arg".

%a3 mean "subsitute the fourth argument here, as if it were an address, not a register name". So in this case the value of the variable "AngelSWI" will be substituted.

%0 means "substitute the first argument here", ie the register which will contain the variable "value" after the asm() statement has completed executing.

Cheers
  Nick

References:
- ARM SWI
  - From: Vijay Deep

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