Re: [hatari-devel] DSP question

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Hi again Doug,

I throw a quick eye into the hatari DSP code, and I think there could be a problem with the L bit of the SR with RTS and RTI instructions.

This should be verified, but I think that if you store a 56 bits accu to some 24bit destination with overflow, the L bit is set correctly, but later if there's a RTS or RTI instruction, the L bit is lost (no sticking behaviour in this special case).

I should verify this on a real falcon and on hatari, but this may be a bug to fix.
Is it what you encontered this afternoon ?



----- Mail original -----
De: "laurent sallafranque" <laurent.sallafranque@xxxxxxx>
À: hatari-devel@xxxxxxxxxxxxxxxxxxx
Envoyé: Vendredi 31 Juillet 2015 15:09:28
Objet: Re: [hatari-devel] DSP question

Hi Doug,

It is implemented into hatari and it should work OK.
So if you encounter a problem here, it's because of a bug into hatari.

I'll look at this in a few days if you really encountered a bug (just tell me).



----- Mail original -----
De: "Douglas Little" <doug694@xxxxxxxxxxxxxx>
À: hatari-devel@xxxxxxxxxxxxxxxxxxx
Envoyé: Vendredi 31 Juillet 2015 14:53:47
Objet: [hatari-devel] DSP question

Does anyone know if the CCR saturation arithmetic / limit flag is implemented in Hatari? 

i.e. when a 56bit accumulator is stored to some 24bit destination, overflows result in saturation and the L bit is set in the CCR and remains sticky until cleared. 

I'm seeing some indication that the L flag is not being set - or if it is set, the JLS jump condition is ignoring it (although I'll need to test it more carefully to be 100% sure). 


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