CodeVisionAVR

3.17 Using an External Startup File

In every program the CodeVisionAVR C compiler automatically generates a code sequence to make the following initializations immediately after the AVR chip reset:

1.interrupt vector jump table

2.global interrupt disable

3.EEPROM access disable

4.Watchdog Timer disable

5.external SRAM access and wait state enable if necessary

6.clear registers R2 … R14

7.clear the SRAM

8.initialize the global variables located in SRAM

9.initialize the Data Stack Pointer register Y

10.initialize the Stack Pointer register SP

11.initialize the UBRR register if necessary

The automatic generation of code sequences 2 to 8 can be disabled by checking the Code Generation|Use an External Startup Initialization File check box in the Project|Configure|C Compiler|Code Generation dialog window. The C compiler will then include, in the generated .asm file, the code sequences from an external file that must be named STARTUP.ASM . This file must be located in the directory where your main C source file resides.

You can write your own STARTUP.ASM file to customize or add some features to your program. The code sequences from this file will be immediately executed after the chip reset.

A basic STARTUP.ASM file is supplied with the compiler distribution and is located in the ..\BIN directory.

Here's the content of this file:

;CodeVisionAVR C Compiler

;(C) 1998-2007 Pavel Haiduc, HP InfoTech s.r.l. ;EXAMPLE STARTUP FILE FOR CodeVisionAVR V1.24.1 OR LATER

;DISABLE THE WATCHDOG

LDI R31,0x18

OUT WDTCR,R31

OUT WDTCR,R30

OUT MCUCR,R30 ;MCUCR=0, NO EXTERNAL SRAM ACCESS

;CLEAR R2-R14

CodeVisionAVR

;CLEAR SRAM

LDI R24,LOW(__CLEAR_SIZE) LDI R25,HIGH(__CLEAR_SIZE) LDI R26,LOW(__CLEAR_START) LDI R27,HIGH(__CLEAR_START)

__CLEAR_SRAM: ST X+,R30 SBIW R24,1

BRNE __CLEAR_SRAM

RJMP __GLOBAL_INI_NEXT __GLOBAL_INI_END:

The __CLEAR_START and __CLEAR_SIZE constants can be changed to specify which area of SRAM to clear at program initialization.

The __GLOBAL_INI_TBL label must be located at the start of a table containing the information necessary to initialize the global variables located in SRAM. This table is automatically generated by the compiler.