Re: [Sdcc-user] help using z80 port

[candido l. r. <c.r...@rc...>]

On Saturday 27 December 2008 03:24:08 pm Richard Gray wrote:
> >From memory, I think the Z80's SP=0 at reset, so the chances are that
>
> initialising of this register is something you're going to want to do
> fairly early on in your code.
>
> There are a couple of ways at least of doing this, but I use my own crt0.s
> file and the --no-std-crt0 compiler switch. The other way is to modify the
> standard crt0.s and replace it with your own version (overwrite the
> standard one), and let the compiler switch default. You /could/ use a piece
> of inline asm in your main() to set SP too, but this is not very elegant
> because main() is itself a function call which would have had it's return
> address pushed onto the stack, albeit uninitialised. I recommend writing
> your crt0.s (copy the standard one and edit it for your own purposes), and
> manually relocate it yourself in your own build.
>
> It might be useful for me to describe how SDCC handles Z80 initialisation -
> and this I have largely found out by experiment: The first to execute (from
> a reset) is crt0.s which will usually start at location 0x0000, the first
> three bytes will then be your reset jump instruction, probably a JMP to
> 0x0100 (labelled 'init'), and then a bunch of definitions of your various
> restart vectors. At location 0x0100 you will probably want to set important
> registers such as SP and any MMU registers if you're using one of the weird
> 'enhanced' Z80's. After this there is a gsinit section (which is empty in
> crt0.s), into which the linker relocates global variable initialisation
> code if need be.
>
> I have found that my init section doesn't appear in the linker's load map
> for some reason, but the code does appear in the eventual .hex file. Just a
> warning incase you're confused!

Thanks  for your help and quick response, I will initialize the stack pointer, 
the only problem that I see with SDCC is that the documentation is not 
generic, it refers to the main port and only in passing  provides references 
about  the remainder ports. This  makes this the documentation a little 
confussing (well a lot :)


Thanks again