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Re: [f-cpu] Reamrks and suggestions about the manual



I agree with all your remark but I think this must be clrified in the 
manual.

Michael Riepe wrote:
> On Sun, Jul 07, 2002 at 02:36:01PM +0200, Thomas Lavergne wrote:
> 
>>Here's some remarks about the ISA decritpion in the manual, some are 
>>little write error, other are remarks about coding of the ISA...
>>
>>Page 94
>>-------
>>
>>You have these two form defined at the start :
>>   addsubs r3, r2, r1
>>   saddsubs r3, r2, r1
>>
>>but no explication of the s suffixe later
> 
> 
> That might mean `saturated'.
> 
> [...]
> 
>>Page 139
>>--------
>>
>>You don't explain the encoding of the flags xtcs, I suppose it was the 
>>same than for the bitop operand but it could be could to say it.
>>
>>At the top of the page you say 'logici.xxxx' so I understand this style 
>>of codding 'logici.0111' like for the logic operand but ater you say 
>>'logici.s' like for bitop, we must clarify this and I think it was best 
>>to have the same form for logic and logici even if we don't have all the 
>>function of logic in logici.
> 
> 
> The `logic[i].xxxx' instruction is obsolete. And it's rather hard to
> grok right because the function encoding is non-intuitive - e.g. does
> `logic.0010 A, B, C' mean `A and not B' or `B and not A'? Is `logic.0001'
> an AND or NOR operation? Both variants are possible, depending on the
> interpretation of the function field.
> 
> ROP2 instructions and bitop use the same function encoding for the
> AND/ANDN/XOR/OR functions (using bits stolen from the 8-bit opcode field).
> According to the VHDL source, the encoding is
> 
> 	000 - and  (ROP2/bitop)
> 	001 - andn (ROP2/bitop)
> 	010 - xor  (ROP2/bitop)
> 	011 - or   (ROP2/bitop)
> 	100 - nor  (ROP2 only)
> 	101 - xnor (ROP2 only)
> 	110 - orn  (ROP2 only)
> 	111 - nand (ROP2 only)
> 
> [...]
> 
>>Page 184
>>--------
>>
>>loopentry use a non standard form (op[8], 0[18], r1[6])
> 
> 
> `loopentry r1' is a special case; it's equivalent to `loadaddri 0, r1'.
> That is, the encoding is (op[8], flags[2], imm[16], r1[6]) with an
> immediate of zero and both flags cleared (D=0 because it's not a data
> address, S=0 because the immediate is not negative).
> 



-- 
Thomas Lavergne                       "Le vrai rêveur est celui qui rêve
                                        de l'impossible."  (Elsa Triolet)
thomas.lavergne@laposte.net
d-12@laposte.net    ICQ:#137121910     http://assoc.wanadoo.fr/thallium/

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