Re: [f-cpu] Error in f-cpu_opcodes.m4 or in manual

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

hi,

Cedric BAIL wrote:

>Cool, someone read the manual ;-)
>
>>I think there was an error here :
>>    
>>
>>In the f-pu_opcodes.m4 the 3 bit for encoding the operation of the 
>>logic.xxx instruction was reserved int the opcode.
>>
>>In the manual the 3 bit field was in the flag part of the instruction 
>>and all form share the same opcode.
>>    
>>
>>What is the good form ?
>>    
>>
>
>I think that it's logical to have this information in the flag part and I don't
>see any reason to see them in the opcode part.
>  
>
i see a good reason for putting some of the information in the opcode.
we have to encode the "combine" and the mux flags and also
have a form with 8-bit immediate data. Since this needs 2 bits more than
the 6-bit register field, some informations has to be pushed back into
the opcode field.

Finally, the .m4 files are often  more up to date than the manual.
This is not always true (now that Cédric maintains it) but the ROP2
operations have been redesigned, tested and refined several times
so i'm confident in the code.

But if at least i had time to read the new version of the manual.....

>Cedric
>
YG

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