#191 [Rabbit] Shadow values for I/O ports

[D-mo]

Trying to write a function that stores I/O port's value in a shadow variable...

This didn't work:

byte reg[256];
inline void reg_write(word num, byte val)
{
    if (num < sizeof(reg) / sizeof(reg[0])) reg[num] = val;
    __sfr __banked __at (num) = val; // ERROR!!!
}

This does work, but requires a function call:

byte reg[256];
void reg_write(word num, byte val) __sdcccall(1)
{
__asm
    ioi
    ld (hl), a
    ; TODO if hl < 256
    ex de, hl
    ld hl, #_reg
    add hl, de
    ld (hl), a
__endasm;
}

I'd like to make this function inline to eliminate call/ret, so I've made it inline. However, at the call site eg:

void main()
{
    reg_write(42, 69);
}

I do not see 42 and 69 being loaded into hl and a:

71 _main::
; NOTHING loaded into hl and a!!!
73  ioi
74  ld  (hl), a
75  ex  de, hl
76  ld  hl, #_reg
77  add hl, de
78  ld  (hl), a

Does anyone have any ideas how I can accomplish that?

[D-mo]

Using some ugly macromancy, I came up with this:

extern byte reg[256];

#define _define_register(name, addr) \
    enum { name = addr }; __sfr __banked __at (name) reg_ ## name; \
    inline void _reg_write_ ## name(byte val) { reg_ ## name = val; reg[name] = val; } \
    inline byte _reg_read_ ## name() { reg[name] = reg_ ## name; return reg[name]; }

#define reg_write(name, val) _reg_write_ ## name(val)
#define reg_read(name) _reg_read_ ## name()

_define_register(gcsr , 0x00)
_define_register(wdtcr, 0x08)
_define_register(wdttr, 0x09)
...

So, now I can do things like:

reg_write(gcsr, reg[gcsr] | 0x03);

If anyone can think of a better solution, please let me know.