学习KEA之ADC之四：FIFO

小咪咪 2023-02-21 11:40 6阅读 0赞

> 作者：曾Jerry 或 大橙员, 250359225@qq.com

[学习KEA之ADC之一：基本介绍][KEA_ADC]  
[学习KEA之ADC之二：查询方式][KEA_ADC 1]  
[学习KEA之ADC之三：中断方式][KEA_ADC 2]  
[学习KEA之ADC之四：FIFO][KEA_ADC_FIFO]  
[学习KEA之ADC之五：自动比较功能][KEA_ADC 3]

## FIFO的意义 ##

要是不使用FIFO功能的话，在多路采集时，ADC会频繁进入中断，这样对MCU来说是个负担，所以需要开启FIFO功能，这样在所有通道采集完后才进入一次中断，提高了效率。

## FIFO有关寄存器 ##

当ADC\_SC4\[AFDEP\]不为0时，便使能了FIFO。 ADC\_SC4\[AFDEP\]也决定了FIFO的深度，其中这个深度最大是8。  
![在这里插入图片描述][20200702194809696.png]

FIFO的模拟输入通道 和 结果通道 是由ADC\_SC1\[ADCH\] 决定的：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ZlaW1lbmcxMTY_size_16_color_FFFFFF_t_70]  
假如FIFO的深度为3，在初始化ADC\_SC1\[ADCH\]时，依次设置了AD7、AD12和AD14，则最终FIFO转换的结果也是对应了AD7、AD12和AD14。有个要注意的是：若ADC\_SC4\[ASCANE\]=1，则开启了扫描方式，只对第一次设置的通道AD7采样，也就是最终的FIFO转换的3个结果都是AD7的。

当FIFO所有通道转换完成的时候，相应的结果将会存取在FIFO的结果通道，不过最终还是通过ADC\_R寄存器来获得。同时，ADC\_SC1\[COCO\]还会置1；如果开启了中断（ADC\_SC1\[AIEN\]=1），还会发生ADC中断。

笔者在调试时，发现寄存器设置的顺序会有影响，建议的顺序如下：

1.  SIM\_SCGC：使能ADC模块
2.  ADC\_APCTL1：把GPIO设置AD管脚
3.  ADC\_SC4：设置FIFO扫描方式、FIFO深度
4.  ADC\_SC3：设置ADC时钟和转换位数
5.  ADC\_SC2：设置软件或硬件启动、参考源
6.  ADC\_SC1：设置单次或连续采样、中断，最后才设置ADC\_SC1\_ADCH

## FIFO的转换时序 ##

FIFO可以由软件或硬件触发，这个由ADC\_SC2\[ADTRG\]决定。

FIFO还有单次采样（Single） 和 连续（Continuous）采样模式，这个由ADC\_SC2\[ADCO\]决定:

*  Single: ADC启动后，采样一次就结束了
 *  Continuous: ADC启动后，会一直地采样  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ZlaW1lbmcxMTY_size_16_color_FFFFFF_t_70 1]  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ZlaW1lbmcxMTY_size_16_color_FFFFFF_t_70 2]  
    ![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ZlaW1lbmcxMTY_size_16_color_FFFFFF_t_70 3]

## FIFO中断例程 ##

/** * FIFO, Continuous, AD7, AD12, AD14, interrupt * * */
    void ADC_Init(void)
    { 
    	SIM_SCGC |= SIM_SCGC_ADC_MASK;   /* Enable bus clock in ADC*/
    
    	ADC_APCTL1 |= ADC_APCTL1_ADPC(1<<7 | 1<<12 | 1<<14); /* Channel selection */
    
    	ADC_SC4 |= ADC_SC4_AFDEP(0b010); /* 3-level FIFO is enabled */
    
    	ADC_SC3 |= ADC_SC3_ADICLK(0b00); /* Bus clock selected, 20 MHz */
    	ADC_SC3 |= ADC_SC3_MODE(0b10);   /* 12-bit mode operation */
    
    	ADC_SC2 |= 0x00;                 /* Software Conversion trigger, disable compare function*/
    	ADC_SC2 |= ADC_SC2_REFSEL(0b01); /* Select VDD and VSS as voltage reference source*/
    
    	ADC_SC1 |= ADC_SC1_ADCO_MASK;    /* Continuous mode operation */
    	ADC_SC1 |= ADC_SC1_AIEN_MASK;    /* ADC Interrupt Enabled */
    
    
    	ADC_SetChannel(7);  /* Enable ADC by setting ADCH bits as low*/
    	ADC_SetChannel(12);
    	ADC_SetChannel(14);
    }
    
    
    /*****************************************************************************//*! * * @brief set ADC channel. * * @param[in] u8Channel adc channel to conversion. * * @return none * * @ Pass/ Fail criteria: none *****************************************************************************/
    void ADC_SetChannel(uint8_t u8Channel)
    { 
        uint32_t u32temp;
    
        u32temp = ADC_SC1;
        u32temp &= ~ADC_SC1_ADCH_MASK;
    
        ADC_SC1 = u32temp | ADC_SC1_ADCH(u8Channel);
    }
    
    /*********************************************************************************************** * * @brief ADC0_IRQHandler - Interrupt for ADC channels, Calls user function. * @param none * @return none * @note 在中断中，不需要查询ADC_SC2_FEMPTY_MASK的 ************************************************************************************************/
    void ADC0_IRQHandler(void)
    { 
    	u16ADC_ConversionBuff[0] = ADC_R;
    	u16ADC_ConversionBuff[1] = ADC_R;
    	u16ADC_ConversionBuff[2] = ADC_R;
    
    	u8ADC_ConversionFlag = 1;
    }

## FIFO查询例程 ##

/** * FIFO, Continuous, AD7, AD12, AD14, no interrupt * * */
    void ADC_Init(void)
    { 
    	SIM_SCGC |= SIM_SCGC_ADC_MASK;   /* Enable bus clock in ADC */
    
    	ADC_APCTL1 |= ADC_APCTL1_ADPC(1<<7 | 1<<12 | 1<<14); /* Channel selection */
    
    	ADC_SC4 &= ~ADC_SC4_ASCANE_MASK; /* FIFO scan mode disabled */
    	ADC_SC4 |= ADC_SC4_AFDEP(0b010); /* 3-level FIFO is enabled */
    
    	ADC_SC3 |= ADC_SC3_ADICLK(0b00); /* Bus clock selected, 20 MHz */
    	ADC_SC3 |= ADC_SC3_MODE(0b10);   /* 12-bit mode operation */
    
    	ADC_SC2 |= 0x00;                 /* Software Conversion trigger, disable compare function*/
    	ADC_SC2 |= ADC_SC2_REFSEL(0b01); /* Select VDD and VSS as voltage reference source*/
    
    	ADC_SC1 |= ADC_SC1_ADCO_MASK;    /* Continuous mode operation */
    	ADC_SC1 &= ~ADC_SC1_AIEN_MASK;    /* Disable ADC Interrupt */
    
    	ADC_SetChannel(7);  /* Enable ADC by setting ADCH bits as low*/
    	ADC_SetChannel(12);
    	ADC_SetChannel(14);
    }
    
    void ADC_SetChannel(uint8_t u8Channel)
    { 
        uint32_t u32temp;
    
        u32temp = ADC_SC1;
        u32temp &= ~ADC_SC1_ADCH_MASK;
    
        ADC_SC1 = u32temp | ADC_SC1_ADCH(u8Channel);
    }
    
    /*********************************************************************************************** * * @brief ADC_FIFO_Poll * @param none * @return none * @note The ADC_SC1[COCO] bit will be set only when all conversions indicated by the analog input channel FIFO complete * whatever software or hardware trigger is set ************************************************************************************************/
    void ADC_FIFO_Poll(uint16_t *buff)
    { 
    	while(!(ADC_SC1 & ADC_SC1_COCO_MASK));
    
    	buff[0] = ADC_R;
    	buff[1] = ADC_R;
    	buff[2] = ADC_R;
    }

## 小结 ##

如果采样次数很多，要求速度比较快的，尽量选择FIFO。

## 附录 ##

完整代码：  
[KEAZN64\_ADC5\_FIFO\_POLL.zip][KEAZN64_ADC5_FIFO_POLL.zip]  
[KEAZN64\_ADC5\_FIFO\_Interrupt.zip][KEAZN64_ADC5_FIFO_Interrupt.zip]

OVER~~

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[KEA_ADC]: https://blog.csdn.net/feimeng116/article/details/106949471
[KEA_ADC 1]: https://blog.csdn.net/feimeng116/article/details/106998567
[KEA_ADC 2]: https://blog.csdn.net/feimeng116/article/details/107003190
[KEA_ADC_FIFO]: https://blog.csdn.net/feimeng116/article/details/107037460
[KEA_ADC 3]: https://blog.csdn.net/feimeng116/article/details/107099831
[20200702194809696.png]: https://img-blog.csdnimg.cn/20200702194809696.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ZlaW1lbmcxMTY_size_16_color_FFFFFF_t_70]: https://img-blog.csdnimg.cn/20200702195455135.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ZlaW1lbmcxMTY=,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ZlaW1lbmcxMTY_size_16_color_FFFFFF_t_70 1]: https://img-blog.csdnimg.cn/2020070220151271.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ZlaW1lbmcxMTY=,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ZlaW1lbmcxMTY_size_16_color_FFFFFF_t_70 2]: https://img-blog.csdnimg.cn/20200702201528963.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ZlaW1lbmcxMTY=,size_16,color_FFFFFF,t_70
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ZlaW1lbmcxMTY_size_16_color_FFFFFF_t_70 3]: https://img-blog.csdnimg.cn/20200702201557736.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ZlaW1lbmcxMTY=,size_16,color_FFFFFF,t_70
[KEAZN64_ADC5_FIFO_POLL.zip]: https://download.csdn.net/download/feimeng116/12571139
[KEAZN64_ADC5_FIFO_Interrupt.zip]: https://download.csdn.net/download/feimeng116/12571137
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ZlaW1lbmcxMTY_size_16_color_FFFFFF_t_70 4]: https://img-blog.csdnimg.cn/20200702205236938.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2ZlaW1lbmcxMTY=,size_16,color_FFFFFF,t_70