General-purpose registers are represented by predefined symbols of the
form r
N (for global registers), where N represents
a number between 0 and 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.
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