On Tue, Dec 04, 2012 at 02:10:42PM +0200, Stefan Kristiansson wrote: > On Mon, Dec 03, 2012 at 03:17:26PM -0500, Peter Gavin wrote: > > Another problem is that l.nop REPORT requires that register 3 be read by > > the pipeline. That's not possible without heavily altering the pipeline > > design--the register addresses accessed by any given instruction need to be > > available immediately without any decoding overhead. So if we introduce a > > debug UART we need to rethink the instructions used to output to it. I > > would suggest adding a separate instruction just for that purpose. > > How is that any different than any other instruction that is using registers > as > source for their data? > I agree that there will be some overhead if actually implemented in hardware, > but so would any other instruction outputting to a debug uart. > > Or am I completely missing your point here?
Actually, reading your message again and giving this some more thought I kind of see what you mean, if you want to have the register output ready when you are doing the instruction decoding, you're kind of screwed since you don't have the register address in the l.nop instruction. Stefan _______________________________________________ OpenRISC mailing list [email protected] http://lists.openrisc.net/listinfo/openrisc
