#774 Out/in instructions

[Ragozini Arturo]

The z80 has In/out instructions that should be possible to inline with standard c sources in order to develop efficient code.
the __asm command is of reduced use when the port or the value have to be taken by the c environment
Other compilers use special instructions/functions that the compiler replaces by out/in outir/inir
could this be added to sdcc ?
I was trying to implement a macro using #define and ___asm___ but apparently there is no way to pass define parameters into asm code

[Philipp Klaus Krause]

You can place variables in the named address space __sfr (see section 3.5.2 in the manual). SDCC will use out/in to access them.

[Ragozini Arturo]

Thanks ! Does it support also outir and inir?

[Philipp Klaus Krause]

Currently, the code generation only uses in and out, no ini, ind, inir, indr, outi, outd, outir or outdr. It does use both variants of in and out, though.

[Ragozini Arturo]

I see also the the sfr solution cannot have the port number as a variable...

This statement
__sfr __at 0x98 DataPort;
does not accept a port number from a C variable

[Philipp Klaus Krause]

The correct way to handle this would be to have a pointer to I/O-space (so you could cast your variable to that pointer type). Unfortunately, that currently doesn't work:

https://sourceforge.net/p/sdcc/bugs/3160/

When that issue gets fixed, outi / outir / ini / inir might then be used to make the access more efficient.

[Ragozini Arturo]

Would it be possible, in general, to allow inline functions where the pre-compiler is able to replace strings or other parameters in the ASM statement?
I was trying something like this:

#define  outir(port,count,addr) __asm__("ld c,#port");__asm__("ld   b,#count");__asm__("ld  hl,#addr");__asm__("outir");

The macro fails, as the pre-compiler is not able to replace strings within the __asm__ instructions. I know that the above macro would give errors for non constants parameters, but it would simplify some loops I have now and the overhead of a function call would almost double the CPU cost of the action.

This is another a possible example: I need to access to banked data and I need to use the bank number. In asm it goes like this:

    // access paged data 
    __asm
    ld  a,#b_DataLevelMap
    ld (#0x9000),a                  ; memory mapper register
    ld (#_curr_bank),a
    __endasm;   

where DataLevelMap is a label in a different bank. I would like to define a small macro where the string "DataLevelMap" can be replaced with any other banked label.
I would define a macro like this:

#define  Pageswap(label) __asm__("ld a,#b_label");__asm__("ld (#0x9000),a");__asm__("ld (#_curr_bank),a");

The above macro fails, as the pre-compiler is not able to replace strings within the __asm__ instructions. The overhead of a function call would almost double the CPU cost of the action.

Are there workarounds?

[Sebastian Riedel]

Maybe use assembly macros? That will definitely ruin jr

void nofunction() __naked{
__asm
.macro moutir port,count,addr
ld c,#port
ld b,#count
ld hl,#addr
outir
.endm
__endasm;
}

called as

__asm
moutir 0 0 0
__endasm;

Or put them in an assembly file and include it in a header.

void nofunction() __naked{
__asm
.include "mymacros.inc"
__endasm;
}

I don’t know if there is a better solution, I usually don’t mix assembly and C.