作者：巨大八爪鱼，本文转载自：巨大八爪鱼的博客

在FPGA里面，AXI DMA这个IP核的主要作用，就是在Verilog语言和C语言之间传输大批量的数据，使用的通信协议为AXI4-Stream。

Xilinx很多IP核都是基于AXI4-Stream协议的，例如浮点数Floating-point IP核，以及以太网Tri Mode Ethernet MAC IP核。要想将Verilog层面的数据搬运到C语言里面处理，就要使用DMA IP核。

本文以浮点数Floating-point IP核将定点数转换为浮点数为例，详细讲解AXI DMA IP核的使用方法。

浮点数IP核的输入输出数据都是32位，协议均为AXI4-Stream。C语言程序首先将要转换的定点数数据通过DMA发送给浮点数IP核，浮点数IP核转换完成后再通过DMA将单精度浮点数结果发回C语言程序，再通过printf打印出来。

定点数的数据类型为int，小数点定在第四位上，即：XXXXXXX.X。整数部分占28位，小数部分占4位。

转换后浮点数的数据类型为float，可以用printf的%f直接打印出来。

工程下载地址：https://pan.baidu.com/s/1SXppHMdhroFT8vGCIysYTQ（提取码：u7wf）

MicroBlaze C语言工程的建法不再赘述，请参阅：https://blog.csdn.net/ZLK1214/article/details/111824576

首先添加Floating-point IP核，作为DMA的外设端：（主存端为BRAM）

这里要注意一下，一定要勾选上TLAST，否则DMA接收端会出现DMA Internal Error的错误：

下面是Xilinx DMA手册里面对DMA Internal Error错误的描述：

添加AXI DMA IP核：

IP核添加好了，但还没有连线：

点击Run Connection Automation，自动连接DMA的S_AXI_LITE接口：

自动连接浮点数IP核的时钟引脚：

添加BRAM控制器：

最终的连线结果：

修改新建的BRAM的容量为64KB：

最终的地址分配方式：

保存Block Design，然后生成Bitstream：

Bitstream生成后，导出xsa文件：

Vitis Platform工程重新导入xsa文件：

修改C程序（helloworld.c）的代码：

（这里面XPAR_BRAM_2_BASEADDR最好改成0xc0000000，因为生成的xparameters.h配置文件里面BRAM号可能有变化） /****************************************************************************** * * Copyright (C) 2009 - 2014 Xilinx, Inc. All rights reserved. * * Permission is hereby granted, free of charge, to any person obtaining a copy * of this software and associated documentation files (the "Software"), to deal * in the Software without restriction, including without limitation the rights * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell * copies of the Software, and to permit persons to whom the Software is * furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in * all copies or substantial portions of the Software. * * Use of the Software is limited solely to applications: * (a) running on a Xilinx device, or * (b) that interact with a Xilinx device through a bus or interconnect. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL * XILINX BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF * OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE * SOFTWARE. * * Except as contained in this notice, the name of the Xilinx shall not be used * in advertising or otherwise to promote the sale, use or other dealings in * this Software without prior written authorization from Xilinx. * ******************************************************************************/

/* * helloworld.c: simple test application * * This application configures UART 16550 to baud rate 9600. * PS7 UART (Zynq) is not initialized by this application, since * bootrom/bsp configures it to baud rate 115200 * * ------------------------------------------------ * | UART TYPE BAUD RATE | * ------------------------------------------------ * uartns550 9600 * uartlite Configurable only in HW design * ps7_uart 115200 (configured by bootrom/bsp) */

#include #include #include "platform.h"

// DMA无法通过AXI Interconnect访问Microblaze本身的BRAM内存 // 只能访问挂接在AXI Interconnect上的内存 #define _countof(arr) (sizeof(arr) / sizeof(*(arr))) typedef struct { int numbers_in[40]; float numbers_out[40]; } BRAM2_Data;

static BRAM2_Data *bram2_data = (BRAM2_Data *)XPAR_BRAM_2_BASEADDR; static XAxiDma xaxidma;

int main(void) { int i, ret = 0; XAxiDma_Config *xaxidma_cfg;

init_platform();

printf("Hello World\n"); printf("Successfully ran Hello World application\n");

// 初始化DMA xaxidma_cfg = XAxiDma_LookupConfig(XPAR_AXIDMA_0_DEVICE_ID); XAxiDma_CfgInitialize(&xaxidma, xaxidma_cfg); ret = XAxiDma_Selftest(&xaxidma); if (ret != XST_SUCCESS) { printf("XAxiDma_Selftest() failed! ret=%d\n", ret); goto err; }

// 初始化DMA的输入数据 printf("numbers_in=%p, numbers_out=%p\n", bram2_data->numbers_in, bram2_data->numbers_out); for (i = 0; i numbers_in); i++) { bram2_data->numbers_in[i] = 314 * (i + 1); if (i & 1) bram2_data->numbers_in[i] = -bram2_data->numbers_in[i]; }

// DMA开始发送数据 (Length参数的单位为字节) ret = XAxiDma_SimpleTransfer(&xaxidma, (uintptr_t)bram2_data->numbers_in, sizeof(bram2_data->numbers_in), XAXIDMA_DMA_TO_DEVICE); if (ret != XST_SUCCESS) { printf("XAxiDma_SimpleTransfer(XAXIDMA_DMA_TO_DEVICE) failed! ret=%d\n", ret); goto err; }

// DMA开始接收数据 ret = XAxiDma_SimpleTransfer(&xaxidma, (uintptr_t)bram2_data->numbers_out, sizeof(bram2_data->numbers_out), XAXIDMA_DEVICE_TO_DMA); if (ret != XST_SUCCESS) { printf("XAxiDma_SimpleTransfer(XAXIDMA_DEVICE_TO_DMA) failed! ret=%d\n", ret); goto err; }

// 等待DMA发送完毕 i = 0; while (XAxiDma_Busy(&xaxidma, XAXIDMA_DMA_TO_DEVICE)) { i++; if (i == 200000) { // 必须确保DMA访问的内存是直接挂接在AXI Interconnect上的 // 否则这里会报DMA Decode Error的错误 (the address request points to an invalid address) printf("DMA Tx timeout! DMASR=0x%08lx\n", XAxiDma_ReadReg(xaxidma.RegBase + XAXIDMA_TX_OFFSET, XAXIDMA_SR_OFFSET)); goto err; } } printf("DMA Tx complete!\n");

// 等待DMA接收完毕 i = 0; while (XAxiDma_Busy(&xaxidma, XAXIDMA_DEVICE_TO_DMA)) { i++; if (i == 200000) { // floating-point IP核的配置里面一定要把A通道的tlast复选框勾选上, 使输入端和输出端都有tlast信号 // 否则s_axis_s2mm_tlast一直为0, DMA以为数据还没接收完, 就会报DMA Internal Error的错误 // (the incoming packet is bigger than what is specified in the DMA length register) printf("DMA Rx timeout! DMASR=0x%08lx\n", XAxiDma_ReadReg(xaxidma.RegBase + XAXIDMA_RX_OFFSET, XAXIDMA_SR_OFFSET)); goto err; } } printf("DMA Rx complete!\n");

err: for (i = 0; i numbers_out); i++) printf("numbers_out[%d]=%f\n", i, bram2_data->numbers_out[i]);

cleanup_platform(); return 0; }

C程序的运行结果：

Hello World Successfully ran Hello World application numbers_in=0xc0000000, numbers_out=0xc00000a0 DMA Tx complete! DMA Rx complete! numbers_out[0]=19.625000 numbers_out[1]=-39.250000 numbers_out[2]=58.875000 numbers_out[3]=-78.500000 numbers_out[4]=98.125000 numbers_out[5]=-117.750000 numbers_out[6]=137.375000 numbers_out[7]=-157.000000 numbers_out[8]=176.625000 numbers_out[9]=-196.250000 numbers_out[10]=215.875000 numbers_out[11]=-235.500000 numbers_out[12]=255.125000 numbers_out[13]=-274.750000 numbers_out[14]=294.375000 numbers_out[15]=-314.000000 numbers_out[16]=333.625000 numbers_out[17]=-353.250000 numbers_out[18]=372.875000 numbers_out[19]=-392.500000 numbers_out[20]=412.125000 numbers_out[21]=-431.750000 numbers_out[22]=451.375000 numbers_out[23]=-471.000000 numbers_out[24]=490.625000 numbers_out[25]=-510.250000 numbers_out[26]=529.875000 numbers_out[27]=-549.500000 numbers_out[28]=569.125000 numbers_out[29]=-588.750000 numbers_out[30]=608.375000 numbers_out[31]=-628.000000 numbers_out[32]=647.625000 numbers_out[33]=-667.250000 numbers_out[34]=686.875000 numbers_out[35]=-706.500000 numbers_out[36]=726.125000 numbers_out[37]=-745.750000 numbers_out[38]=765.375000 numbers_out[39]=-785.000000

接下来讲一下我们刚才禁用掉的Scatter Gather接口的用法。取消禁用后，之前的C代码就不能运行了。 之前没有启用Scatter Gather的时候，我们一次只能提交一个DMA请求，等这个DMA请求的数据传输完毕后，我们才能提交下一个DMA传输请求。 有了Scatter Gather接口，我们就可以一次性提交很多很多DMA请求，然后CPU去干其他的事情。这可以大大提高传输效率。 除此以外，Scatter Gather还可以将多个位于不同内存地址的缓冲区合并成一个AXI4-Stream数据包传输。

下面的示例演示了如何利用Scatter Gather功能批量收发3组数据包。 启用了Scatter Gather后，DMA里面多出了一个M_AXI_SG接口，点击Run Connection Automation，连接到AXI Interconnect上：

Vivado工程Generate Bitstream，然后导出xsa文件。回到Vitis后，必须把Platform工程删了重建，不然XPAR_AXI_DMA_0_INCLUDE_SG的值得不到更新。

原有的C程序不再可用，修改一下程序代码： /****************************************************************************** * * Copyright (C) 2009 - 2014 Xilinx, Inc. All rights reserved. * * Permission is hereby granted, free of charge, to any person obtaining a copy * of this software and associated documentation files (the "Software"), to deal * in the Software without restriction, including without limitation the rights * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell * copies of the Software, and to permit persons to whom the Software is * furnished to do so, subject to the following conditions: * * The above copyright notice and this permission notice shall be included in * all copies or substantial portions of the Software. * * Use of the Software is limited solely to applications: * (a) running on a Xilinx device, or * (b) that interact with a Xilinx device through a bus or interconnect. * * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL * XILINX BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, * WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF * OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE * SOFTWARE. * * Except as contained in this notice, the name of the Xilinx shall not be used * in advertising or otherwise to promote the sale, use or other dealings in * this Software without prior written authorization from Xilinx. * ******************************************************************************/

/* * helloworld.c: simple test application * * This application configures UART 16550 to baud rate 9600. * PS7 UART (Zynq) is not initialized by this application, since * bootrom/bsp configures it to baud rate 115200 * * ------------------------------------------------ * | UART TYPE BAUD RATE | * ------------------------------------------------ * uartns550 9600 * uartlite Configurable only in HW design * ps7_uart 115200 (configured by bootrom/bsp) */

#include #include #include "platform.h"

/* Xilinx的官方例程：C:\Xilinx\Vitis\2020.1\data\embeddedsw\XilinxProcessorIPLib\drivers\axidma_v9_11\examples\xaxidma_example_sg_poll.c */

// DMA无法通过AXI Interconnect访问Microblaze本身的BRAM内存 // 只能访问挂接在AXI Interconnect上的内存 #define _countof(arr) (sizeof(arr) / sizeof(*(arr))) typedef struct { int numbers_in[40]; float numbers_out[40]; } BRAM2_Data;

typedef struct { uint8_t txbuf[640]; uint8_t rxbuf[640]; } BRAM2_BdRingBuffer;

static BRAM2_Data *bram2_data = (BRAM2_Data *)0xc0000000; static BRAM2_BdRingBuffer *bram2_bdringbuf = (BRAM2_BdRingBuffer *)0xc0008000; static XAxiDma xaxidma;

int main(void) { int i, n, ret = 0; XAxiDma_Bd *bd, *p; XAxiDma_BdRing *txring, *rxring; XAxiDma_Config *cfg;

init_platform();

printf("Hello World\n"); printf("Successfully ran Hello World application\n");

// 初始化DMA cfg = XAxiDma_LookupConfig(XPAR_AXIDMA_0_DEVICE_ID); XAxiDma_CfgInitialize(&xaxidma, cfg); ret = XAxiDma_Selftest(&xaxidma); if (ret != XST_SUCCESS) { printf("XAxiDma_Selftest() failed! ret=%d\n", ret); goto err; }

if (!XAxiDma_HasSg(&xaxidma)) { printf("XPAR_AXI_DMA_0_INCLUDE_SG=%d\n", XPAR_AXI_DMA_0_INCLUDE_SG); printf("Please recreate and build Vitis platform project!\n"); goto err; }

// 初始化DMA的输入数据 printf("[0] numbers_in=%p, numbers_out=%p\n", bram2_data[0].numbers_in, bram2_data[0].numbers_out); printf("[1] numbers_in=%p, numbers_out=%p\n", bram2_data[1].numbers_in, bram2_data[1].numbers_out); printf("[2] numbers_in=%p, numbers_out=%p\n", bram2_data[2].numbers_in, bram2_data[2].numbers_out); for (i = 0; i { bram2_data[0].numbers_in[i] = 314 * (i + 1); bram2_data[1].numbers_in[i] = -141 * (i + 1); bram2_data[2].numbers_in[i] = -2718 * (i + 1); if (i & 1) { bram2_data[0].numbers_in[i] = -bram2_data[0].numbers_in[i]; bram2_data[1].numbers_in[i] = -bram2_data[1].numbers_in[i]; bram2_data[2].numbers_in[i] = -bram2_data[2].numbers_in[i]; } }

// 配置DMA发送描述符 txring = XAxiDma_GetTxRing(&xaxidma); n = XAxiDma_BdRingCntCalc(XAXIDMA_BD_MINIMUM_ALIGNMENT, sizeof(bram2_bdringbuf->txbuf)); ret = XAxiDma_BdRingCreate(txring, (uintptr_t)bram2_bdringbuf->txbuf, (uintptr_t)bram2_bdringbuf->txbuf, XAXIDMA_BD_MINIMUM_ALIGNMENT, n); if (ret != XST_SUCCESS) { printf("XAxiDma_BdRingCreate(txring) failed! ret=%d\n", ret); goto err; } printf("BdRing Tx count: %d\n", n);

ret = XAxiDma_BdRingAlloc(txring, 3, &bd); if (ret != XST_SUCCESS) { printf("XAxiDma_BdRingAlloc(txring) failed! ret=%d\n", ret); goto err; }

p = bd; for (i = 0; i { XAxiDma_BdSetBufAddr(p, (uintptr_t)bram2_data[i].numbers_in); XAxiDma_BdSetLength(p, sizeof(bram2_data[i].numbers_in), txring->MaxTransferLen); XAxiDma_BdSetCtrl(p, XAXIDMA_BD_CTRL_TXSOF_MASK | XAXIDMA_BD_CTRL_TXEOF_MASK); XAxiDma_BdSetId(p, i); p = (XAxiDma_Bd *)XAxiDma_BdRingNext(txring, p); }

ret = XAxiDma_BdRingToHw(txring, 3, bd); if (ret != XST_SUCCESS) { printf("XAxiDma_BdRingToHw(txring) failed! ret=%d\n", ret); goto err; }

// 配置DMA接收描述符 rxring = XAxiDma_GetRxRing(&xaxidma); n = XAxiDma_BdRingCntCalc(XAXIDMA_BD_MINIMUM_ALIGNMENT, sizeof(bram2_bdringbuf->rxbuf)); ret = XAxiDma_BdRingCreate(rxring, (uintptr_t)bram2_bdringbuf->rxbuf, (uintptr_t)bram2_bdringbuf->rxbuf, XAXIDMA_BD_MINIMUM_ALIGNMENT, n); if (ret != XST_SUCCESS) { printf("XAxiDma_BdRingCreate(rxring) failed! ret=%d\n", ret); goto err; } printf("BdRing Rx count: %d\n", n);

ret = XAxiDma_BdRingAlloc(rxring, 3, &bd); if (ret != XST_SUCCESS) { printf("XAxiDma_BdRingAlloc(rxring) failed! ret=%d\n", ret); goto err; }

p = bd; for (i = 0; i { XAxiDma_BdSetBufAddr(p, (uintptr_t)bram2_data[i].numbers_out); XAxiDma_BdSetLength(p, sizeof(bram2_data[i].numbers_out), rxring->MaxTransferLen); XAxiDma_BdSetCtrl(p, 0); XAxiDma_BdSetId(p, i); p = (XAxiDma_Bd *)XAxiDma_BdRingNext(rxring, p); }

ret = XAxiDma_BdRingToHw(rxring, 3, bd); if (ret != XST_SUCCESS) { printf("XAxiDma_BdRingToHw(rxring) failed! ret=%d\n", ret); goto err; }

// 开始发送数据 ret = XAxiDma_BdRingStart(txring); if (ret != XST_SUCCESS) { printf("XAxiDma_BdRingStart(txring) failed! ret=%d\n", ret); goto err; }

// 开始接收数据 ret = XAxiDma_BdRingStart(rxring); if (ret != XST_SUCCESS) { printf("XAxiDma_BdRingStart(rxring) failed! ret=%d\n", ret); goto err; }

// 等待收发结束 n = 0; while (n { // 检查发送是否结束 ret = XAxiDma_BdRingFromHw(txring, XAXIDMA_ALL_BDS, &bd); if (ret != 0) { n += ret; p = bd; for (i = 0; i { printf("DMA Tx%lu Complete!\n", XAxiDma_BdGetId(p)); p = (XAxiDma_Bd *)XAxiDma_BdRingNext(txring, p); }

ret = XAxiDma_BdRingFree(txring, ret, bd); if (ret != XST_SUCCESS) printf("XAxiDma_BdRingFree(txring) failed! ret=%d\n", ret); }

// 检查接收是否结束 ret = XAxiDma_BdRingFromHw(rxring, XAXIDMA_ALL_BDS, &bd); if (ret != 0) { n += ret; p = bd; for (i = 0; i { printf("DMA Rx%lu Complete!\n", XAxiDma_BdGetId(p)); p = (XAxiDma_Bd *)XAxiDma_BdRingNext(rxring, p); }

ret = XAxiDma_BdRingFree(rxring, ret, bd); if (ret != XST_SUCCESS) printf("XAxiDma_BdRingFree(rxring) failed! ret=%d\n", ret); } }

err: for (i = 0; i printf("numbers_out[%d]=%f,%f,%f\n", i, bram2_data[0].numbers_out[i], bram2_data[1].numbers_out[i], bram2_data[2].numbers_out[i]);

cleanup_platform(); return 0; }

程序运行结果：

Hello World Successfully ran Hello World application [0] numbers_in=0xc0000000, numbers_out=0xc00000a0 [1] numbers_in=0xc0000140, numbers_out=0xc00001e0 [2] numbers_in=0xc0000280, numbers_out=0xc0000320 BdRing Tx count: 10 BdRing Rx count: 10 DMA Tx0 Complete! DMA Tx1 Complete! DMA Tx2 Complete! DMA Rx0 Complete! DMA Rx1 Complete! DMA Rx2 Complete! numbers_out[0]=19.625000,-8.812500,-169.875000 numbers_out[1]=-39.250000,17.625000,339.750000 numbers_out[2]=58.875000,-26.437500,-509.625000 numbers_out[3]=-78.500000,35.250000,679.500000 numbers_out[4]=98.125000,-44.062500,-849.375000 numbers_out[5]=-117.750000,52.875000,1019.250000 numbers_out[6]=137.375000,-61.687500,-1189.125000 numbers_out[7]=-157.000000,70.500000,1359.000000 numbers_out[8]=176.625000,-79.312500,-1528.875000 numbers_out[9]=-196.250000,88.125000,1698.750000 numbers_out[10]=215.875000,-96.937500,-1868.625000 numbers_out[11]=-235.500000,105.750000,2038.500000 numbers_out[12]=255.125000,-114.562500,-2208.375000 numbers_out[13]=-274.750000,123.375000,2378.250000 numbers_out[14]=294.375000,-132.187500,-2548.125000 numbers_out[15]=-314.000000,141.000000,2718.000000 numbers_out[16]=333.625000,-149.812500,-2887.875000 numbers_out[17]=-353.250000,158.625000,3057.750000 numbers_out[18]=372.875000,-167.437500,-3227.625000 numbers_out[19]=-392.500000,176.250000,3397.500000 numbers_out[20]=412.125000,-185.062500,-3567.375000 numbers_out[21]=-431.750000,193.875000,3737.250000 numbers_out[22]=451.375000,-202.687500,-3907.125000 numbers_out[23]=-471.000000,211.500000,4077.000000 numbers_out[24]=490.625000,-220.312500,-4246.875000 numbers_out[25]=-510.250000,229.125000,4416.750000 numbers_out[26]=529.875000,-237.937500,-4586.625000 numbers_out[27]=-549.500000,246.750000,4756.500000 numbers_out[28]=569.125000,-255.562500,-4926.375000 numbers_out[29]=-588.750000,264.375000,5096.250000 numbers_out[30]=608.375000,-273.187500,-5266.125000 numbers_out[31]=-628.000000,282.000000,5436.000000 numbers_out[32]=647.625000,-290.812500,-5605.875000 numbers_out[33]=-667.250000,299.625000,5775.750000 numbers_out[34]=686.875000,-308.437500,-5945.625000 numbers_out[35]=-706.500000,317.250000,6115.500000 numbers_out[36]=726.125000,-326.062500,-6285.375000 numbers_out[37]=-745.750000,334.875000,6455.250000 numbers_out[38]=765.375000,-343.687500,-6625.125000 numbers_out[39]=-785.000000,352.500000,6795.000000