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What is r13 used for in PowerPC architecture

Question asked by jinyu zhang on Aug 15, 2018

Morning, everyone:


I am using the Codewarrior ver8.8 for debuging the MPC855T. I have found that in the interrupt processing function, once after restoring the r13, when it reach a global variation, the debug would send an Exception, which is a Machine check Exception. So what is the r13 used for, and how would restoring it cause the exception?


I also refer to the new found project. In the group runtime, there is a Interrupt vector file eppc_exception.asm. And found that the saved and restored GPRs not including the r13-r31. As I know, r14-r31 is the temporary registers, non-volatile.When an interrupt occurs, how protect the registers from altering? Does the Codewarrior compiler add some codes to save them?


Any discussion and reply will be appreciated.


Thanks and good day!