Lpc2000

Not really an LPC2100 issue, but this is a helpful group.. I need some
remedial help in thumb/arm interoperability in GCC, particularly with
assembler gets involved.  For instance, how __asm__ macros for basics
like enable()/restore() know what mode the calling code is using.  Also,
for assembler routines in .s files (context switch, etc.) it seems that
the architecture would best support the *caller* knowing whether a
routine is ARM/Thumb, although this is not the way it seems to work.

Are there any good code examples that get into the hows and whys of
issues like these?