Re: [f-cpu] Supported Instructions

["Christophe" <christophe.avoinne@laposte.net>]

> >Well, instead of just having the IP, we can also get the values of the
> >concerned registers.
> >
> >For example, if we have : "mac r16,r4,r5", three SRs would have the contents
of
> >r16, r4 and r5 while triggering the invalid instruction interruption. Or
three
> >fields in our CMB to get those contents.
> >
> >Those SRs could have names like SR_REG1, SR_REG2 and SR_REG3.
> >
> >(hopefully there is only register operands for other instructions than
"load"
> >or "store")
>
> Do you think this is a good idea? IMO then you need to know
> (i.e. implement) about parts of the opcode already. The
> best method would be to just treat it as 'unknown' and
> let the emulation take control. In that case you are also
> free to add opcodes later that have not been thought of
> today, e.g. additional application specific opcodes that
> may only be implemented in few members of the f-cpu family
> or offsprings.

In fact, whatever is the opcode, F-CPU just extracts the three fields and give
us their contents. The opcode could never use one or two of those registers
(one or two operands instructions) so it doesn't make a difference. It is the
software to do whatever it wants with this info. So F-CPU really lets the
emulation take control, because it is only the emulation code which knows what
to do with. Such a feature could be disabled or better thought.

>
> <not to offend you or f-cpu>
> In leon for example I use some of the coprocessor opcodes
> for completely different things. It was not intended by
> the SPARC definition that way but helps me to get faster
> execution and debugging capabilities for my application.
> </not to offend you or f-cpu>

We are okay

> With f-cpu I would wish for such free opcode blocks just
> to be able to add e.g. special opcodes for grafical use
> when f-cpu is controlling a 3D grafic human interface in
> the future. Keep it free to be extendable even in ways
> that may not be very common today but may get very much
> wanted in the next 30 years (didn't YG intended that?).

Do such free opcode blocks trigger an exception anyhow ?


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