General-purpose registers are represented by predefined symbols of the
form `rN' (for global registers), where N represents
a number between
15. The leading
letters may be in either upper or lower case; for example, `r13'
and `R7' are both valid register names.
Register names `PC', `SP' and `SR' cannot be used as register names and will be treated as variables. Use `r0', `r1', and `r2' instead.