Zilog Z8F0130 - Manual (Page 281)

UM013037-1212 Deviations from ANSI C
Zilog Developer Studio II – Z8 Encore!
User Manual
257
Double Treated as Float
The Z8 Encore! C-Compiler does not support a double-precision floating-point type. The
type
double is accepted but is treated as if it were float .
const Keyword and ROM
The Z8 Encore! C-Compiler by default assumes const in RAM and places const vari-
ables without any storage qualifications in RData for the small model and EData for the
large model. With the
const in RAM option in affect, the C-Compiler follows the ANSI
C standard rules for const parameters.
However, the C-Compiler also provides a deprecated option to place such const variables
in ROM memory instead. When this option is selected, the treatment of the const key-
word is emphatically non-ANSI. Specifically, when this option is selected, the const key-
word is treated as equivalent to rom . Then, the function prototype
void foo (const char* src);
implies that the src string is in ROM memory, and any code that calls foo should pass
only a const or rom string as src string argument. This restriction comes because the Z8
Encore! microcontroller has different machine instructions for accessing its different
memory spaces (LDC, LD, and LDX). This is a deviation from ANSI C. The compiler
reports an “Incompatible data types” error for code that does not follow the preceding
restriction.
Under the ANSI standard, the const qualification on a parameter merely implies that the
function cannot modify the parameter and a non- const qualified argument can be passed
as the corresponding parameter.
The effect of this deviation from the standard is primarily that, in code that must be porta-
ble for all options of the compiler and linker (such as the source code for library functions
provided by the compiler), parameters cannot be declared
const .
On new applications, Zilog discourages this use of the const keyword to place data in
ROM. Zilog recommends declaring constant data (such as tables) using the rom keyword
instead. Where portability is a consideration, this can easily be done by preprocessor mac-
ros.
For example:
#ifdef __EZ8__

# define ROM rom

#else

# define ROM const

#endif

ROM struct TableElement[] table = { /* stuff */};