On Sun, Dec 2, 2012 at 6:46 PM, Peter Gavin <[email protected]> wrote: > 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.
Stefan has also mentioned previously that he'd like an easy way of transferring the SR[FLAG] bit to a GPR more easily. Perhaps we can come up with something to accommodate all of these flags. > >> >> 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 Thanks, Julius _______________________________________________ OpenRISC mailing list [email protected] http://lists.openrisc.net/listinfo/openrisc
