Astrobe Forum

Posted: **Fri Feb 04, 2022 9:13 am**

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?

Posted: **Fri Feb 04, 2022 10:34 am**

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)

If you then look at the RISC5 compiler modification history you will see the following entry for 2018:

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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.

https://people.inf.ethz.ch/wirth/news.txt

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.

Posted: **Mon Feb 07, 2022 6:34 am**

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.

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Register R13

Register R13

Re: Register R13

Re: Register R13