Address pointers with Program Counter

[Lonewolf10]

Hi,

I have some code that I have been working on for some time (due to many distractions...). Now that it is pretty much finished I am trying to convert it so that it is compatible with systems with fast memory.

Clearly I don't fully understand the limitations of using the program counter as I get the following errors when assembling (with DevPac 3.18):

Error: linker format restriction at line 1007 in file DD_L-Strikes.s33
 1007 01.0000009A 41FAC7C2                     lea.l   sprite0(pc),a0

Error: linker format restriction at line 1016 in file DD_L-Strikes.s33
 1016 01.000000AC 4BFA0000                     lea.l   screen(pc),a5

...and I know someone will ask to see example code, so here it is:

pre_title_screen:

    jsr         setup_screen2           ;setup screen and colours (logo_cop)

                                        ;*** Clear screen ***
    moveq       #4-1,d7                 ;bitplanes to clear (e.g. 4=4-1)
    lea.l       screen,a0               ;destination address
.next_plane
                                        ;clear 597 lines...
    move.w      #0,d0                   ;modulo (e.g. 40-width for Lowres)
    move.w      #%1001010101010100,d1   ;size of area, in BLTSIZE format
                                        ;(%hhhhhhhhhhwwwwww) h=lines,w=words
    jsr         clear_screen            ;clear main menu text from screen
    adda.l      IDAT_img_plane,a0       ;point to next bitplane
    dbra        d7,.next_plane

                                        ;*** Clear sprites 0-7 and 0b-7b ***
    lea.l       sprite0(pc),a0          ;start of data to clear
    move.w      #0,d0                   ;modulo (e.g. 40-width for Lowres)
    move.w      #%0010000000010111,d1   ;size of area, in BLTSIZE format
                                        ;(%hhhhhhhhhhwwwwww) h=lines,w=words
                                        ;5888 bytes = 2944 words
                                        ;           = 128 words * 23 'lines'
    jsr	        clear_screen

                                        ;*** Decode & display title image ***
    lea.l       screen(pc),a5           ;set destination
    move.l      a5,IDAT_img_dest
    lea.l       title+12,a6             ;address of sourcefile+offset to IHDR
    move.w      #1,IDAT_image_type      ;1=Ppaint, 2=MSpaint
    jsr	        decode_png

    WaitLine MAX_SCANLINE

What am I doing wrong?

[Don_Adan]

Try
lea Sprite1,A0
not
lea Sprite1(pc),A0

[Toni Wilen]

sprite0 and screen are probably in different section == pc relative addressing is not possible.

[hooverphonique]

yes, Toni is on the right track there..

[phx]

Toni is certainly right for the 'screen' reference. But 'sprite0' seems to be in the same section, although the distance is larger than 32K. Look at the $c7c2 in Devpac's output:

1007 01.0000009A 41FAC7C2                     lea.l   sprite0(pc),a0

Unfortunately both cases generate the same error message.

BTW, a PC-relative reference to a different section is not always illegal. This is just a problem for AmigaDOS, because you cannot predict the address of a section. The scatter-loader will allocate individual memory for each section and relocate it there.

The AtariST would have no problem with PC-referencing data-symbols from the text-section, as text, data and bss are always loaded as a single unit. Also Unixes have fixed section addresses.

I would like to know if Devpac-Atari (GenST) would show the same error...

[Lonewolf10]

Originally Posted by Toni Wilen

sprite0 and screen are probably in different section == pc relative addressing is not possible.

'sprite0' and 'screen' are both in a BSS section, at the end of the file. All the code is in a CODE section at the start of the file.
In short, you are correct

Originally Posted by phx

BTW, a PC-relative reference to a different section is not always illegal.

So it would work only if the address being referenced lies within the range (16KB?) of the current PC address?

[hooverphonique]

Originally Posted by Lonewolf10

So it would work only if the address being referenced lies within the range (16KB?) of the current PC address?

on amiga it is not possible to use a pc-relative address to a different section, because the assembler/linker cannot know up front, what the address offset between the two will be ;-)

[Lonewolf10]

Ok, thanks for all the help guys

[meynaf]

Originally Posted by phx

I would like to know if Devpac-Atari (GenST) would show the same error...

I did that all the time in my ST days, and Devpac 2 didn't show an error at all.