Zahada C atmel studio

[Tomáš Mazouch]

Vypada to, ze blbec je prekladac, protoze pouzije BRGE na unsigned. To, 
ze se skok provede, je OK, protoze podle Atmeliho popisu instrukcni sady 
ma BRGE skocit, pokud je N XOR V == 0 (coz je).

   TomM


Dne 3.5.2014 17:14, Jaroslav Buchta napsal(a):
> Tak vzhledem k pocasi se nimram s krokovanim v assembleru a 
> posloupnost je takovato (c je v R11):
>
>             DrawChar(c, x, y, FontTahoma_12);
> 00001354  MOV R24,R11        Copy register
> 00001355  MOVW R22,R16        Copy register pair
> 00001356  MOVW R20,R14        Copy register pair
> 00001357  MOVW R18,R8        Copy register pair
> 00001358  CALL 0x000011D1        Call subroutine
>             x += w + 2;
> 0000135A  ADIW R28,0x02        Add immediate to word
> 0000135B  ADD R16,R28        Add without carry
> 0000135C  ADC R17,R29        Add with carry
>             c++;
> 0000135D  INC R11        Increment
>             if (c >= 0x80) c = 0x20;
> 0000135E  BRGE PC+0x04        Branch if greater or equal, signed
> 0000135F  CLR R11        Clear Register
> 00001360  SET         Set T in SREG
> 00001361  BLD R11,5        Bit load from T to register
>         while (y < 320)
> 00001362  LDI R24,0x40        Load immediate
>
> posloupnost instrukci je tedy spravna, ale:
>
> INC R11 nastavi
> pro 0x20-0x7E priznaky N=0, V=0, S=0 - skok se provede
> pro 0x7F priznaky N=1, V=1, S=0 - skok se PROVEDE COZ JE SPATNE!!!
> pro 0x80 v dalsi iteraci pak N=1, V=0, S=1 a skok se konecne 
> neprovede, c se nastavi na 0x20 ale ten znak 0x80 to predtim vytiskne 
> a protoze neni v tabulce, mam na displeji kousek rozsypaneho caje...
>
> Je to zavada prekladace, nebo je to nekde v errata zavada procesoru 
> ATMEGA16 ??? (docela stary kousek) Podminka je snad napsana spravne. 
> Prekladac je normalne nainstalovan jako soucast atmel studia a verze + 
> parametry:
>
> Building file: .././Test1.c
>         Invoking: AVR/GNU C Compiler : 
> (AVR_8_bit_GNU_Toolchain_3.4.1_830) 4.6.2
>         "C:\Program Files (x86)\Atmel\Atmel Studio 
> 6.0\extensions\Atmel\AVRGCC\3.4.1.95\AVRToolchain\bin\avr-gcc.exe" 
> -funsigned-char -funsigned-bitfields -O1 -fpack-struct -fshort-enums 
> -g2 -Wall -c -std=gnu99 -MD -MP -MF "Test1.d" -MT"Test1.d" 
> -MT"Test1.o"  -mmcu=atmega16   -o"Test1.o" ".././Test1.c"
>         .././Test1.c: In function 'TestSquare':
>
> Kdyz se c definuje jako volatile, prelozi se to takto:
>
>             c++;
> 00001362  LDD R24,Y+1        Load indirect with displacement
> 00001363  SUBI R24,0xFF        Subtract immediate
> 00001364  STD Y+1,R24        Store indirect with displacement
>             if (c >= 0x80) c = 0x20;
> 00001365  LDD R24,Y+1        Load indirect with displacement
> 00001366  TST R24        Test for Zero or Minus
> 00001367  BRGE PC+0x03        Branch if greater or equal, signed
>
> coz uz funguje samozrejme OK.
>
> Dne 3. 5. 2014 16:45, Lukas Burda napsal(a):
>> A kdyz to w deklarujete na zacatku? Takhle mi to kdysi dalalo s gcc
>> nejaky problem, ale uz prd vim o co vlastne slo. Jen jsem si odnesl
>> zvyk to tak nedelat.
>>
>> L.
>>
>>
>>
>> Saturday, May 3, 2014, 1:56:21 PM, you wrote:
>>
>>> Muze mi nekdo vysvetli, proc v Atmel studiu se mi pri nasledujicim kodu
>>>           int16_t x = 0;
>>>           int16_t y = CharHeight(FontTahoma_12)+2;
>>>           uint8_t c = 0x20;
>>>           DrawChar(0x7f, x, y, FontTahoma_12);
>>>           while (y < 320)
>>>           {
>>>               uint8_t w = CharWidth(c, FontTahoma_12);
>>> <-----------------------------------------
>>>               if (x + w > 240)
>>>               {
>>>                   x = 0;
>>>                   y += CharHeight(FontTahoma_12) + 2;
>>>                   continue;
>>>               }
>>>               DrawChar(c, x, y, FontTahoma_12);
>>>               x += w + 2;
>>>               c++;
>>>               if (c >= 0x80) c = 0x20;
>>>           }
>>> dostane do oznacene funkce hodnota c =0x80??? Evidentne je to
>>> optimalizaci (O1), pokud ji vypnu, funguje to OK, asi by pomohly i jine
>>> finty na promenne (volatile atp.) ale co je sakra spatne? Pri krokovani
>>> to ruzne poskakuje po radcich a nezjistim nic.
>>> Mozna jsem jen pri sobote slepej nebo si na necem sedim, pujdu se 
>>> projet
>>> na kole radsi ;-)
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