On Sun, Dec 2, 2012 at 1:11 PM, Julius Baxter <[email protected]>wrote:
> 1. Accessing SPRs with insufficient privileges > > I reckon accessing SPRs which are only accessible in supervisor mode, > while in user mode, should basically do nothing - writing should > behave like a l.nop and reading should return zero, as if the SPR is > unimplemented. > > > http://opencores.org/or1k/Architecture_Specification#Accessing_SPRs_with_insufficient_privileges > Yes, this makes sense. On a related note, sometimes I wonder if the CY and OV bits should be directly readable from userspace, so that user code can use hardware overflow detection without relying on operating system support. The CY flag is indirectly readable with addc, but the OV flag is not. They could be duplicated into a read-only SPR that's accessible from user mode. > 2. Optional overflow/carry detection and (range) exception. > Good idea. > 3. Behaviour when AECR/AESR not present > This makes sense. > 4. "Signed" in name of l.add[ic] and l.sub > Looks good. -Pete
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