Hello Peter,

> In the main routine a printf gets the wrong value:
>
> extern __data uint8 * __data sys_rstack;
>
> // string for LCD output
> #define STR_LEN 80
> __xdata uint8 str[STR_LEN];
>
> main()
> {
>         sprintf (str,"%x", (uint8) *sys_rstack);
>         lcd_print(2, str);
>
>       generates:
>                             707 ;       main.c:107: sprintf (str,"%x",
> (uint8) *
> sys_rstack);
>    01B4 A9 10               708         mov     r1,_sys_rstack
>    01B6 87 07               709         mov     ar7,@r1
>    01B8 C0 07               710         push    ar7
>    01BA 74 53               711         mov     a,#__str_3
>    01BC C0 E0               712         push    acc
>    01BE 74 7E               713         mov     a,#(__str_3 >> 8)
>    01C0 C0 E0               714         push    acc
>    01C2 74 80               715         mov     a,#0x80
>    01C4 C0 E0               716         push    acc
>    01C6 74 DC               717         mov     a,#_str
>    01C8 C0 E0               718         push    acc
>    01CA 74 01               719         mov     a,#(_str >> 8)
>    01CC C0 E0               720         push    acc
>    01CE E4                  721         clr     a
>    01CF C0 E0               722         push    acc
>    01D1 12 7D 15            723         lcall   _sprintf
>    01D4 E5 81               724         mov     a,sp
>    01D6 24 F9               725         add     a,#0xf9
>    01D8 F5 81               726         mov     sp,a
>                             727 ;       main.c:108: lcd_print(2, str);
>
> The code above appears to be loading the contents of
> sys_rstack (at 0x10 in data) in to r7 but something undesirable happens
> after that (which may well be operator error on my part).

Since you use an explicit cast to char on the parameter passed to a
varargs function (sprintf) the value is not passed as an int as normal.
This is an extension to save memory. But then your formatter must also
tell it to expect a char instead of an int as %x does. Maybe it's better
to just remove the inline cast.

HTH,
Maarten

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