Re: [Fx2lib-devel] Linker Options

[Dennis M. <de...@ub...>]

>
> The problem is more generic than that. Is there a way for the linker to fail when two sections (which may be abs sections or not) overlap. Setting the code/data etc sizes "--code-size" does protect against relative code sections from overrunning the boundary, but there is no protection for abs sections. 
>
> The problem is the FX2 has 2 alignment requirements, the vectors must be on a 256 byte page boundary and the various descriptors - in order to be sent automatically - need to be word aligned. The fx1 does not have the descriptor alignment limitation, so its descriptor can just be defined in regular .c files.
>
> One thing that can help is to move the interrupt vectors to low memory, the descriptors after that - which can be tucked tightly after the interrupt vectors (no page alignment issues, just word). And then you can move the starting --code-addr to after the descriptors. This does not eliminate the possible overlap, but does confine it to just one place.
>
> I think I remember using something like "--code-loc 0x0200 --code-size 0x1200 --xram-loc 0x1400 --xram-size 0x0030" on the fx2.
>   

I like the idea of putting the jump table first.  SDCC generates a bunch 
of interrupt code for the USB and gpif interrupts at the interrupt 
locations 13-whatever but these are redundant with the jump table (and 
unused).  Seems like it would be a good idea to overlay the jump table 
in that area.  I think the jump table takes less bytes than the 
interrupt code SDCC generates does.  

I'll play around with that when I get a second.  I think there is always 
going to be some responsibility on the person compiling the firmware to 
make sure their descriptor (yes the whole descriptor/strings etc) fit 
within the space allotted.  It might work fine for a while but then you 
might add some long device names or company names or something and find 
your firmware doesn't work any longer.

-Dennis