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I'm trying to configure some software that has different start addresses based on how the FLASH gets updated. If FLASH is updated via a UART then the code should start at 0 otherwise it should start at 24K. I thought the following would work - where FLASH_VIA_UART is defined in the C51 preprocessor symbols menu.
#ifdef FLASH_VIA_UART #define RUNTIME_CODE_START_ADDRESS (RUNTIME_CODE_START_AT_0H) #else #define RUNTIME_CODE_START_ADDRESS (RUNTIME_CODE_START_AT_24kH) #endif
However, this doesn't work. Instead I have to hardcode it by commenting out everything but the 2nd line. Then the software works fine.
The RUNTIME_CODE_START_ADDRESS define could be used in other defines and macros so I suspect that there is a scope problem or something. Note that this code is in a .h file which is then used in multiple files.
Rather than just have the flag defined or not, it may be "safer" to require it to have a specific value - that way you can catch any problems where the definition is accidentally missing; eg,
#ifdef FLASH_VIA_UART // It's defined - check its value, and use it if valid #if FLASH_VIA_UART == 2 #define RUNTIME_CODE_START_ADDRESS (RUNTIME_CODE_START_AT_0H) #elif FLASH_VIA_UART == 3 #define RUNTIME_CODE_START_ADDRESS (RUNTIME_CODE_START_AT_24kH) #else #error Invalid value for FLASH_VIA_UART #endif #else // It's not defined #error FLASH_VIA_UART must be defined #endif
Note that I've avoided 0 and 1 as values - as these are likely to be used by (some) compilers when the symbol is defined without a specific value...