[Libre-soc-bugs] [Bug 1135] add FPSCR and Rounding classes to ieee754fpu

[bugzilla-daemon at libre-soc.org]

https://bugs.libre-soc.org/show_bug.cgi?id=1135

--- Comment #4 from Luke Kenneth Casson Leighton <lkcl at lkcl.net> ---
log notes on how "speculative execution" is to work.

it is NOT repeat NOT to be implemented in the way that you describe.

it is to be implemented by performing a Shadow-Hold that does nothing
more complex than:

* hold off the write to the regfile until it is known
  - if the exception has occurred (in which case "CANCEL WRITE" is raised)
  - if there is NO CHANCE of the exception occurring
    (in which case "DROP SHADOW" is raised)

it's really very simple.

but what you need to write right now is the infrastructure that *when*
we get to doing OoO it is easy to do so because everything is in place...

but we are NOT repeat NOT going to smash down the entire 4 years of planning
and design work to create a completely new set of ideas by implementing
something that is unauthorised and has not been discussed or reviewed...
and neither are we going to implement something that would take SIX MONTHS
to perform that review.

please stick to the original micro-architectural plan that was put in place
*well over three years ago*.

and *do not* deviate from what i have written here, nor attempt *in any way*
to implement ANY form of "speculative" pipelining, system, infrastructure,
or design.

the components that i designed, as-designed may be used in *any* type of
micro-architecture.

we happen to be starting with the simplest because it is most straightforward
and gets results the fastest and with the least complications.

further grants can cover *incremental* improvements.

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