Hi,
In my compeny we are develope Embedded SW on the AT89C51RD2. The SW include BL & APP that compile together (due to no enough flash space). The purpose of this SW is to be able to upgrade only the Application section by writing the flash memory (The BL section is stored from 0x0054 to 0x5000 in the flash and the app is from 0x5001 to 0xFFFF). In order to be able to do it, i seted all the function in the BL section and the constants to absolute address in the flash memory (By using ?CO?, ?PR? - linker directive) and the uninitialized global variables were seted to fixed address by using _at_ keybord. The global variables of the App (0x5000 - 0xFFFF) section are free to link by linker.
My questions are: 1. What happened with the uninitialized global variables, where are they stored ? I know the the compiler initilaized thaem to zero but is there BSS locaation ? if so where is it ? and is it posible to set it for a absolute address in the XDATA ? 2. If the first sw was compiled and burn to the device and i changed only the application section (global variable was added) and compile it again but i want burn only the application (0x5000 and above) by using __api_wr_code_page, how is the SW will know about the new address of the new global ? 3. Where is the address of the global variables were stored (not initilaized, i know that the init global variables data were save in the C_INITSEG segment and it is copy to the RAM after the STARTUP and befure the main)?
I know it is complicated (and my english is bit bad) but i realy need your help. Thanks.