WARNING L16: UNCALLED SEGMENT, IGNORED FOR OVERLAY PROCESS

问题遇到的现象和发生背景

直接复制ADC,DAC转换的例程还是出现这类警告？？

运行结果及报错内容

WARNING L16: UNCALLED SEGMENT, IGNORED FOR OVERLAY PROCESS
SEGMENT: ?PR?I2C_START?I2C
UNRESOLVED EXTERNAL SYMBOL
SYMBOL: _DAC_PCF8591
MODULE: \Objects\DAC_self.obj (DAC_SELF)
REFERENCE MADE TO UNRESOLVED EXTERNAL
SYMBOL: _DAC_PCF8591
MODULE: .Objects\DAC_self.obj (DAC_SELF)
ADDRESS: 08B7H
Program Size: data=23.2 xdata=0 code=775
creating hex file from ".\Objects\DAC_self"
".\Objects\DAC_self" - 0 Error(s), 9 Warning(s)
Build Time Elapsed: 00:00:01

我的解答思路和尝试过的方法

明明原程序可以，复制过来就有警告？

WARNING L16: UNCALLED SEGMENT, IGNORED FOR OVERLAY PROCESS
SEGMENT: ?PR?I2C_START?I2C
意思是说I2C_START没有用到，这个要注意，I2C通信中Stary信号必不可少，所以你要检查下你的I2C相关，是不是有通信漏掉了Start信号

UNRESOLVED EXTERNAL SYMBOL
SYMBOL: _DAC_PCF8591
MODULE: \Objects\DAC_self.obj (DAC_SELF)
DAC_self.c文件中的_DAC_PCF8591有声明，但找不到定义