Re: [hatari-devel] Re: [hatari-users] DSP emulation - MPY #immediate

[Laurent Sallafranque <laurent.sallafranque@xxxxxxx>]

Hi,

I'm not reading it.
I'll subscribe immediatly.

I've just answeared to Doug and Thomas, I copy my answear here for 
tracability.

-------

Hi Doug,

I've given a look at the mpy instruction again.

Are you sure of you here ?

I've tested the opcode $0114d0 in a DSP simulator I have here, and it 
returns me the correct opcode (ie mpy x0,#20,a)

But, it seems not to be a DSP 56001 instruction.
I don't think we use the same doc. Be careful, there's one doc on 
internet which clams to be for 56001 but is for DSP 56000 or something 
else.

I've done a quick try with qasm V0.13b and it return me an error on this 
line :
[90]    mpy    x0,#20,a

error at line 90: operand error

NB: I use it often to do some DSP tests and it generally compiles.

Are you sure your opcode compiles and run on a real falcon ?

Laurent

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Le 27/01/2013 17:36, Eero Tamminen a écrit :
> Hi,
>
> As Laurent hasn't commented this, maybe he's not reading
> the users mailing list. -> I forward this to hatari-devel.
>
> 	- Eero
>
> On perjantai 25 tammikuu 2013, Douglas Little wrote:
> > I think I see a bug (?) in the DSP56k emulation. I'm not absolutely sure
> > yet but I checked what I could against the DSP56001 User Manual before
> > posting...
> >
> >
> > When assembling the 'multiply immediate 2^-n' (i.e. the n-bit right
> > shift) instruction e.g.
> >
> >    mpy x0, #4, a
> >    move          a0,D    ; D = (x0>>4)
> >
> >    mpy x0, #(24-4), a
> >    move          a1,D    ; D = (x0<<4)
> >
> >
> > ...Hatari issues an illegal instruction error when executing the MPY
> > opcode. The disassembly looks like this:
> >
> > p:08bb  0114d0         (00 cyc)  dc $0114d0        <--- MPY x0,#20,a
> > p:08bc  0af080 000902  (07 cyc)  jmp p:$0902
> >
> >
> > The encoding for this instruction can be found on page A231 of the
> > DSP56000 Family Manual and $0114d0 seems to be the correct opcode
> > encoding. The same opcode can be found in the DSP56001 User Manual.
> >
> >
> > There is no hurry for this but would nice to be able to use this
> > instruction. It's the only way to shift N bits without clobbering an
> > extra register with another move :-)