Dual Display station - software description

Coding conventions

Software configuration: Using #define settings

By setting or removing #define precompiler statements, pieces of code can be easily added or removed. One example of this is enabling or disabling all debug functionality in a release:

#define DEBUG_ENABLED

All such statements are collected in the top of the file <main.h>.

Loading C strings from FLASH

The IAR C compiler for AVR processors is by default configured for reading strings from DATA segment (RAM). This requires the compiler to copy the strings from FLASH to RAM during initialisation/cstartup. After that, the stings can be used in normal "ANSI C style":

printf("Hello World!");

Loading the strings to RAM is required for the strings to be manipulated during run-time. But by using special-designed functions instead of printf(), this can be avoided. Printing strings is done with a separate function, which loads text from FLASH only.

This could be achieved by pre-defining all strings:

BYTE flash *string_example = "Hello World!";

... and it would be used this way:

print_string(string_example);

This is not an easy code to read. Instead, the string could be used the normal way by making a few configurations:

• The CSTR segment containing strings is configured as a CODE segment (FLASH) in the linker file <lnk3s4kb_MODIFIED.xcl>.
• The function using the strings must cast the pointer from RAM to FLASH type. This is because the pointer is actually pointing at the correct address in FLASH, but the compiler still believes it is a RAM pointer. For example:

void print_string(BYTE *string_temp)

{

BYTE flash *string;

string = (BYTE flash *)(WORD)string_temp;

...

}

"string_temp" is an invalid RAM pointer, but the FLASH pointer "string" can now be used normally instead.

• In some cases, pre-defined strings are preferred if a string is used multiple times. But now the problem is vice versa: The function is expecting a RAM pointer, but the pointer is in this case actually FLASH. So we have to cast the pointer to RAM to be able to compile the code:

BYTE flash *string_example = "Hello World!"; print_string( (BYTE *)(WORD)string_example );