Re: [f-cpu] register move in 1 x-bar cycle

[Yann Guidon <whygee@f-cpu.org>]

hi,

jaap stolk wrote:
> 
> hi,
> 
> this could be a simple typo, but
> according to the manual (chapter 6)
> a register move looks like this:
> 
> Fetch > Decod         > Xbar      > Register write
>        (+reg read)     (+schedule)
>        (+bypass check)
> 
> i would like to turn that into
> 
> Fetch > Decod         > Xbar    >  Xbar  > Register w.
>        (+reg read)     (+schedule)
>        (+bypass check)
> 
> ther will be no extra lost cycle (the next instuction
> will use a direct bypass instead of a delayed bypass)
> http://f-cpu.seul.org/whygee/parinux/conf_yg.html
> seems to conferm this.
> 
> i tryed doing it in one cycle in the c simulator,
> but it has the folowing complications:
> 
> -its a reversed bypass (so we need extra hardware
>  to bypass FROM the read bus TO the write bus)
> -we can't use the schedule queue for the register
>  write (schedule cycle is to late), so we have
>  to control the xbar directly from the decoder.
> -the x-bar needs to ignore these commands from the
>  decoder in normal operation.
> 
> can we change it into two x-bar cycles ?

you're right, the manual is not up to date.

btw : could we add a modification date to each instruction
in the manual ? This would help people understand
what document to trust if there is such another problem.

> jaap.
WHYGEE
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