[参考译文] MSP430FR2355：extern 限定符不起作用？？

https://e2e.ti.com/support/microcontrollers/msp-low-power-microcontrollers-group/msp430/f/msp-low-power-microcontroller-forum/1013592/msp430fr2355-extern-specifier-not-working

有人能告诉我我下面缺少的是什么… 将 main.h 代码放置在 main.c 文件中并进行所有编译...但是我希望消除所有混乱并将结构定义放置在 main.h 中  当我这么做时、我会遇到大量类似如下的错误：

 第13行：警告#78-D：此声明没有存储类或类型说明符
 第13行：错误#66：预期为"；"

main.c

#include "main.h"

void main(void)
{
    extern DAC_Handle_t ControlVoltage;


    WDTCTL = WDTPW | WDTHOLD;

    DAC_Init(&ControlVoltage);


}

main.h

#ifndef INC_MAIN_H_
#define INC_MAIN_H_

#include "dac.h"

ControlVoltage.pDACx = DAC0;
ControlVoltage.DAC_Config.OA_Source = INTERNAL;
ControlVoltage.DAC_Config.OA_Speed = HIGH_SPEED;
ControlVoltage.DAC_Config.OA_InputConfig = NONINVERTING;
ControlVoltage.DAC_Config.OA_GainConfig = BUFFER;
ControlVoltage.DAC_Config.DAC_Value = 100;

#endif /* INC_MAIN_H_ */

dac.h --此文件位于 main.h 之外的单独文件夹下，但包含在编译器选项中。

#include <msp430.h>
#include <stdint.h>

typedef struct
{
    volatile uint16_t SACOA;       /*OpAmp input config register            Offset 0x00 */
    volatile uint16_t SACPGA;      /*OpAmp gain register                    Offset 0x02 */
    volatile uint16_t SACDAC;      /*DAC setup register                     Offset 0x04 */
    volatile uint16_t SACDAT;      /*DAC data register                      Offset 0x06 */
    volatile uint16_t SACDATSTS;   /*DAC flag status register               Offset 0x08 */
}DAC_RegDef_t;

typedef struct
{
    volatile uint16_t PMMCTL[3];   /*pmm control register                   Offset 0x00 - 0x04 */
}PMM_RegDef_t;

#define DAC0   (DAC_RegDef_t *)SAC0_BASE
#define DAC1   (DAC_RegDef_t *)SAC1_BASE
#define DAC2   (DAC_RegDef_t *)SAC2_BASE
#define DAC3   (DAC_RegDef_t *)SAC3_BASE
#define PMM    (PMM_RegDef_t *)PMM_BASE


typedef struct
{
    uint8_t OA_InputConfig;         /*values @OA_INPUT */
    uint8_t OA_GainConfig;          /*values @OA_GAIN */
    uint8_t OA_Source;                /*values @OA_SOURCE */
    uint8_t OA_Speed;               /*values @OA_SPEED */
    uint8_t DAC_Value;
}DAC_Config_t;

/*
 * @OA_INPUT
 */
#define INVERTING      0
#define NONINVERTING   1

/*
 * @OA_GAIN
 */
#define BUFFER          1
#define INV_GAIN1       BUFFER
#define INV_GAIN2       INV_GAIN1 + 1
#define INV_GAIN4       INV_GAIN2 + 1
#define INV_GAIN8       INV_GAIN4 + 1
#define INV_GAIN16      INV_GAIN8 + 1
#define INV_GAIN25      INV_GAIN16 + 1
#define INV_GAIN32      INV_GAIN25 + 1
#define NONINV_GAIN2    BUFFER
#define NONINV_GAIN3    NONINV_GAIN2 + 1
#define NONINV_GAIN5    NONINV_GAIN3 + 1
#define NONINV_GAIN9    NONINV_GAIN5 + 1
#define NONINV_GAIN17   NONINV_GAIN9 + 1
#define NONINV_GAIN26   NONINV_GAIN17 + 1
#define NONINV_GAIN33   NONINV_GAIN26 + 1

/*
 * @OA_SOURCE
 */
#define INTERNAL      0
#define EXTERNAL      1

/*
 * @OA_SPEED
 */
#define HIGH_SPEED  0
#define LOW_SPEED   1

/*
 * handle structure for GPIO pin
 */
typedef struct
{
    DAC_RegDef_t *pDACx; /*holds base address of GPIO port to which pin belongs */
    DAC_Config_t DAC_Config; /*holds GPIO pin configuration settings */
}DAC_Handle_t;


/*
 * general
 */
#define SPEED 9
#define UNLOCK 0xA5

void DAC_Init(DAC_Handle_t *pDACHandle);

#endif /* DRIVERS_INC_DAC_H_ */