STM32F407配置了ADC，连续采样转换，但实际效果是打开AD后只采集一次，配置情况见如下代码段，不知道什么原因，大神帮忙看看。

GPIO_InitTypeDef GPIO_InitStructure;
ADC_InitTypeDef ADC_InitStruct;

RCC_APB2PeriphClockCmd(RCC_APB2Periph_ADC2, ENABLE);    
RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOC, ENABLE);   

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_0; 
GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AN;
GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
GPIO_Init(GPIOC, &GPIO_InitStructure);

ADC_InitStruct.ADC_Resolution = ADC_Resolution_12b;
ADC_InitStruct.ADC_ScanConvMode = DISABLE;
ADC_InitStruct.ADC_ContinuousConvMode = ENABLE;
ADC_InitStruct.ADC_ExternalTrigConvEdge = ADC_ExternalTrigConvEdge_None;
ADC_InitStruct.ADC_DataAlign = ADC_DataAlign_Right;
ADC_InitStruct.ADC_NbrOfConversion = 1;        
ADC_Init(ADC2, &ADC_InitStruct);

ADC_RegularChannelConfig(ADC2, ADC_Channel_10, 1, ADC_SampleTime_15Cycles);
ADC_ContinuousModeCmd(ADC2, ENABLE);
ADC_Cmd(ADC2, ENABLE);

ADC_SoftwareStartConv(ADC2);