On Tue, Nov 20, 2012 at 6:21 PM, Julius Baxter <[email protected]>wrote:
> This is probably a contentious point, but why shouldn't writing to > unimplemented SPRs be alright? Does it say anything about this in the > spec? > I remember coming across this problem in the past, and I think my initial implementation of mtspr would trigger an error or something like that for unknown SPRs, because it wasn't clear what else should happen. Then I found the mtspr we're talking about now, and so I explicitly allowed zero to be written to the TTMR register without raising an error. At some point I changed it so they don't raise an error, but instead just print a warning to the screen and resume with no other effect. I think this is the only time an unimplemented SPR gets written to in libgloss, newlib, or libgcc. I don't think the manual explicitly states that writing unimplemented SPRs has no effect. A search of a few related terms didn't bring it up, and it's not in section 4.3. -Pete
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