Register R13

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ORG.incR allocates registers up to R11. R12 is MT, R14 is SP, and R15 is LNK. What about R13, may I use it, or does it have a special purpose as well?

[cfbsoftware]

Refer to Section 8.1 Layout and run-time organization of the Project Oberon (2013) Documentation:

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R13 base address for variables in the current module SB (static base)

However, the RISC5 compiler modification history states:

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20180720 - Update compiler: ORP.Mod.txt and ORG.Mod.txt
  Cash (* Cache? *) for base adr of global variables "curSB" has been removed from ORG.Mod.
  Removal of this optimization makes compiler simpler.

However, I would not recommend using R13 for your own purposes unless you intend to maintain your own customised version of the RISC5 compiler as well.

[gray]

Thanks for the pointers. I don't have intention to change the compiler to use R13, but I am grinding my teeth on an in-circuit debugger, and an otherwise unused register could be handy from assembly code.