GD32F450设置定时器输入捕获下降沿触发DMA

首先，需要初始化定时器和DMA。具体代码如下：

/* 使能定时器时钟 */
rcu_periph_clock_enable(RCU_TIMER0);

/* 使能DMA时钟 */
rcu_periph_clock_enable(RCU_DMA0);

/* 配置定时器 */
timer_deinit(TIMER0);
timer_parameter_struct timer_initpara;
timer_struct_para_init(&timer_initpara);
timer_initpara.prescaler         = 71;
timer_initpara.alignedmode       = TIMER_COUNTER_EDGE;
timer_initpara.counterdirection = TIMER_COUNTER_UP;
timer_initpara.period            = 0xFFFF;
timer_initpara.clockdivision     = TIMER_CKDIV_DIV1;
timer_init(TIMER0, &timer_initpara);

/* 配置DMA */
dma_deinit(DMA0, DMA_CH0);
dma_parameter_struct dma_initpara;
dma_struct_para_init(&dma_initpara);
dma_initpara.direction         = DMA_PERIPHERAL_TO_MEMORY;
dma_initpara.memory_addr       = (uint32_t)&capture_value;
dma_initpara.memory_inc        = DMA_MEMORY_INC_ENABLE;
dma_initpara.memory_width      = DMA_MEMORY_WIDTH_32BIT;
dma_initpara.number            = 1;
dma_initpara.periph_addr       = (uint32_t)&TIMER_CAR(TIMER0);
dma_initpara.periph_inc        = DMA_PERIPH_INC_DISABLE;
dma_initpara.periph_width      = DMA_PERIPHERAL_WIDTH_32BIT;
dma_initpara.priority          = DMA_PRIORITY_ULTRA_HIGH;
dma_init(DMA0, DMA_CH0, &dma_initpara);

/* 配置定时器输入捕获 */
timer_input_capture_parameter_struct timer_icinitpara;
timer_ic_struct_para_init(&timer_icinitpara);
timer_icinitpara.icpolarity  = TIMER_IC_POLARITY_FALLING;
timer_icinitpara.icselection = TIMER_IC_SELECTION_DIRECTTI;
timer_icinitpara.icprescaler = TIMER_IC_PSC_DIV1;
timer_icinitpara.icfilter    = 0x0;
timer_input_capture_init(TIMER0, TIMER_CH_0, &timer_icinitpara);

接着，需要开启DMA传输和定时器。具体代码如下：

/* 使能DMA通道 */
dma_channel_enable(DMA0, DMA_CH0);

/* 使能定时器 */
timer_enable(TIMER0);

最后，在定时器中断处理函数中，读取捕获值并重新配置DMA传输。具体代码如下：

void TIMER0_IRQHandler(void)
{
    if (timer_interrupt_flag_get(TIMER0, TIMER_INT_CH0) != RESET)
    {
        /* 清除定时器中断标志 */
        timer_interrupt_flag_clear(TIMER0, TIMER_INT_CH0);

        /* 获取捕获值 */
        uint32_t capture_value = timer_channel_capture_value_register_get(TIMER0, TIMER_CH_0);

        /* 配置DMA传输 */
        dma_memory0_address_config(DMA0, DMA_CH0, (uint32_t)&capture_value);
        dma_channel_enable(DMA0, DMA_CH0);
    }
}

这样，当定时器0的输入捕获通道0检测到下降沿时，就会触发DMA传输了。需要注意的是，上述代码仅供参考，具体实现还需要根据实际需求进行调整。