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Applies to: C51 C Compiler
Information in this article applies to:
I have noticed that the Reset vector jumps to some assembler code, yet my project is entirely written in C. What is this assembler code? Is it junk?
The reset vector jumps to the startup code (which initializes the stack pointer among other things) which is written in assembler. The startup code calls the main function. If you step through this code in dScope, you should see that eventually your main function is called.
The startup code may be found in the file LIBSTARTUP.A51 in your C51 installation. Also, if you have some global or other static variables that are initialized when declared, then the code in the file LIBINIT.A51 will be called before the main function to initialize these variables. These files are included automatically when using C.
If you look at the address that the reset vector jumps to, you should see that it matches the start address of the ?C_C51STARTUP segment in the .m51 file. For example, below the start address is 0737H:
TYPE BASE LENGTH RELOCATION SEGMENT NAME ----------------------------------------------------- * * * * * * * D A T A M E M O R Y * * * * * * * REG 0000H 0008H ABSOLUTE "REG BANK 0" DATA 0008H 0015H UNIT _DATA_GROUP_ 001DH 0003H *** GAP *** BIT 0020H.0 0001H.1 UNIT _BIT_GROUP_ 0021H.1 0000H.7 *** GAP *** IDATA 0022H 0001H UNIT ?STACK * * * * * * * C O D E M E M O R Y * * * * * * * CODE 0000H 0003H ABSOLUTE 0003H 02FDH *** GAP *** CODE 0300H 0355H UNIT ?PR?PRINTF?PRINTF CODE 0655H 008EH UNIT ?C?LIB_CODE CODE 06E3H 0027H UNIT ?PR?PUTCHAR?PUTCHAR CODE 070AH 0025H UNIT ?PR?MAIN?HELLO CODE 072FH 0008H UNIT ?CO?HELLO CODE 0737H 0006H UNIT ?C_C51STARTUP 073DH 38C3H *** GAP *** CODE 4000H 0001H UNIT ?PR?ISR41?HELLO
Article last edited on: 2005-07-15 13:22:21
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