通过设置全局变量I2S0,I2S1触发DMA机制的疑问求解答

在跟踪esp32-web-camera的代码时，看到了通过设置全局变量I2S0,I2S1，触发DMA的机制，对于结构体i2s_dev_t的各字段不是很理解，不懂哪里有这方面的文档，另外通过设置变量I2S0而实现DMA机制，能不能帮忙描述下？

以下是样例中，ll_cam.c中设置I2S0的代码
bool ll_cam_start(cam_obj_t *cam, int frame_pos)
{
    I2S0.conf.rx_start = 0;

    I2S_ISR_ENABLE(in_suc_eof);

    I2S0.conf.rx_reset = 1;
    I2S0.conf.rx_reset = 0;
    I2S0.conf.rx_fifo_reset = 1;
    I2S0.conf.rx_fifo_reset = 0;
    I2S0.lc_conf.in_rst = 1;
    I2S0.lc_conf.in_rst = 0;
    I2S0.lc_conf.ahbm_fifo_rst = 1;
    I2S0.lc_conf.ahbm_fifo_rst = 0;
    I2S0.lc_conf.ahbm_rst = 1;
    I2S0.lc_conf.ahbm_rst = 0;

    I2S0.rx_eof_num = cam->dma_half_buffer_size / sizeof(dma_elem_t);
    I2S0.in_link.addr = ((uint32_t)&cam->dma[0]) & 0xfffff;

    I2S0.in_link.start = 1;
    I2S0.conf.rx_start = 1;
    return true;
}