PG021

AXI DMA：AXI Direct Memory Access

AXI DMA为内存和AXI4-Stream外设之间提供了高带宽的直接内存访问，其可选的S/G功能可以将CPU从数据搬运任务中解放出来。

 AXI DMA通过AXI4-LITE接口对寄存器做一些配置和获取

MM2S：MemoryMap to Stream 存储器映射（AXI4-Full）到AXI4-Stream

S2MM：Stream to MemoryMap 存储器映射 AXI4-Stream到AXI4-Full

MM2S和S2MM传输完成后都会产生中断

 时钟

m_axi_mm2s_aclk for mm2s interface

m_axi_s2mm_aclk for s2mm interface

s_axi_lite_aclk for axi4-lite control interface

m_axi_sg_clk for Scatter Gather Interface

AXI DMA编程顺序：

Direct Register Mode（简单DMA）

此模式提供了在MM2S和S2MM通道上进行简单DMA传输的配置，只需要较少的FPGA资源。 

通过访问DMACR、源地址或目的地址寄存器和长度寄存器发起DMA传输。

当传输完成后，如果使能了产生中断输出，那么DMASR寄存器相关联的通道位会有效。

DMA的MM2S（存储器映射到Stream）通道的启动顺序

1. Start the MM2S channel running by setting the run/stop bit to 1 (MM2S_DMACR.RS = 1).

2. If desired, enable interrupts by writing a 1 to MM2S_DMACR. IOC_IrqEn and MM2S_DMACR.Err_IrqEn.

3. Write a valid source address to the MM2S_SA register.

4. Write the number of bytes to transfer in the MM2S_LENGTH register.

DMA的S2MM（Stream到存储器映射）通道的启动顺序

1. Start the S2MM channel running by setting the run/stop bit to 1 (S2MM_DMACR.RS = 1).

2. If desired, enable interrupts by writing a 1 to S2MM_DMACR.IOC_IrqEn and S2MM_DMACR.Err_IrqEn.

3. Write a valid destination address to the S2MM_DA register

4. Write the length in bytes of the receive buffer in the S2MM_LENGTH register