Re: [avr-libc-dev] Error when using lagre memory addresses

[gouy yann]

hello,

I suspect you will ask to write a bug report for the problem not to be
forgiven!

regards.

   Yann

 --- Per Arnold Blåsmo <address@hidden> a écrit : 
> Hi,
> During my work with adapting avg-gcc to a new processor (AT90SC3232CS) I
> have discovered a problem regarding addressing that I think is not
> working in the generated code.
> 
> I would like some comments on this from some of you more expert than me
> on this :-)
> 
> Consider the following code:
> ----
> #include <avr/io.h>
> #include <avr/pgmspace.h>
> 
> #define FROMADDR 0x100000L
> #define TOADDR1 (uint8_t *)0x200
> #define TOADDR2    (uint8_t *)0x100
> 
> int main(void)
> {
>     uint8_t *p_to_addr1= TOADDR1;
>     uint8_t *p_to_addr2= TOADDR2;
>     uint32_t from_addr = FROMADDR;
>     uint8_t size = 255;
> 
>     while(size--){
>         *p_to_addr1++ = pgm_read_byte_far(from_addr++);
>     }
>     size=255;
>     *p_to_addr1 = TOADDR1;
>     while(size--){
>         *p_to_addr2++ = *p_to_addr1++;
>     }
> 
> }
> ----
> 
> Compile for an ATmega128 it gives the following assembly:
> (and yes I know it would not work in real life, but I try to show a
> point her :-)
> 
> ----
> int main(void)
> {
>   62:    cf ef           ldi    r28, 0xFF    ; 255
>   64:    dc e0           ldi    r29, 0x0C    ; 12
>   66:    de bf           out    0x3e, r29    ; 62
>   68:    cd bf           out    0x3d, r28    ; 61
>     uint8_t *p_to_addr1= TOADDR1;
>   6a:    00 e0           ldi    r16, 0x00    ; 0
>   6c:    12 e0           ldi    r17, 0x02    ; 2
>     uint8_t *p_to_addr2= TOADDR2;
>   6e:    ee 24           eor    r14, r14
>   70:    ff 24           eor    r15, r15
>   72:    68 94           set
>   74:    f0 f8           bld    r15, 0
>     uint32_t from_addr = FROMADDR;
>   76:    40 e0           ldi    r20, 0x00    ; 0
>   78:    50 e0           ldi    r21, 0x00    ; 0
>   7a:    60 e1           ldi    r22, 0x10    ; 16
>   7c:    70 e0           ldi    r23, 0x00    ; 0
>     uint8_t size = 255;
> 
>     while(size--){
>         *p_to_addr1++ = pgm_read_byte_far(from_addr++);
>   7e:    ce ef           ldi    r28, 0xFE    ; 254
>   80:    db 01           movw    r26, r22
>   82:    ca 01           movw    r24, r20
>   84:    4f 5f           subi    r20, 0xFF    ; 255
>   86:    5f 4f           sbci    r21, 0xFF    ; 255
>   88:    6f 4f           sbci    r22, 0xFF    ; 255
>   8a:    7f 4f           sbci    r23, 0xFF    ; 255
>   8c:    98 01           movw    r18, r16
>   8e:    0f 5f           subi    r16, 0xFF    ; 255
>   90:    1f 4f           sbci    r17, 0xFF    ; 255
>   92:    ab bf           out    0x3b, r26    ; 59   <= 0x3b = RAMPZ set
> to 0x10
>   94:    fc 01           movw    r30, r24
>   96:    87 91           elpm    r24, Z+
>   98:    f9 01           movw    r30, r18
>   9a:    80 83           st    Z, r24               <= this one should
> store to 0x0200 but stores to 0x100200 instead
>   9c:    c1 50           subi    r28, 0x01    ; 1
>   9e:    80 f7           brcc    .-32         ; 0x80
>     }
>     size=255;
>     *p_to_addr1 = TOADDR1;
>   a0:    f8 01           movw    r30, r16
>   a2:    10 82           st    Z, r1
>     while(size--){
>         *p_to_addr2++ = *p_to_addr1++;
>   a4:    ce ef           ldi    r28, 0xFE    ; 254
>   a6:    f8 01           movw    r30, r16
>   a8:    81 91           ld    r24, Z+            <= this one should
> load from 0x0200 but loads from 0x100200
>   aa:    8f 01           movw    r16, r30
>   ac:    f7 01           movw    r30, r14
>   ae:    81 93           st    Z+, r24            <= this one should
> store in 0x0100 but stores in 0x100100
>   b0:    7f 01           movw    r14, r30
>   b2:    c1 50           subi    r28, 0x01    ; 1
>   b4:    c0 f7           brcc    .-16         ; 0xa6
>     }
> 
> }
> 
> -----------
> 
> This code will not work as intended.
> 
> As you can see I use a 'from address' that is 24 bit put into a long (32
> bit).
> To read from this address I use 'pgm_read_byte_far'. 'pgm_read_byte_far'
> correctly uses
> RAMPZ (0x3b) to address the memory location ((RAMPZ:Z) = 0x100000).
> 
> The problem is that RAMPZ does not get reset after used. That clutters
> the use of Z later in the code.
> 
> My solution to this so far has been to include a line likethis:
> 
>     __asm__ volatile ("out     %0, 0x0" : : "I" (_SFR_IO_ADDR(RAMPZ)));
>     // Hack to reset RAMPZ after it is used
> 
> Anyone like to comment on this or/and suggest another work-around?
> 
> Per A.
> 
> 
> _______________________________________________
> AVR-libc-dev mailing list
> address@hidden
> http://lists.nongnu.org/mailman/listinfo/avr-libc-dev
>  


        

        
                
Découvrez le nouveau Yahoo! Mail : 250 Mo d'espace de stockage pour vos mails ! 
Créez votre Yahoo! Mail sur http://fr.mail.yahoo.com/