2012/12/4 Stefan Kristiansson <[email protected]>: > 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.opencores.org/listinfo/openrisc
Would it help to use 5 bits in the nop immediate for a register number? -- Olof Kindgren ______________________________________________ ORSoC Website: www.orsoc.se Email: [email protected] ______________________________________________ FPGA, ASIC, DSP - embedded SoC design _______________________________________________ OpenRISC mailing list [email protected] http://lists.openrisc.net/listinfo/openrisc
