在Altera SoC DE1板卡(🐞)上跑完整的卷(🦍)积(📖)神经网络
这次为大家详细展示一个利用卷积神经网络实现图(📩)片自动分类的例程。
神经网络的优点:自动从数据中学习经验知识,无需复杂的模型和算法。
缺点:有监督学习,需要大量的带标签数据;参(🧐)数(🏦)量太少时容易过拟合,泛(🍏)化能力差,参数量太大时训练收敛很(👠)慢(有可能需要几个月到(👅)几年)。
为了(😗)克服上述缺点,人们发掘了各种计算资源,包括多核CPU、GPU、DSP、ASIC、FPGA,甚至使(✒)用模(🛏)拟电路。
使用(😟)CPU实现卷积神经网络比较方便调试,但性能太差,一般人们(🗻)都选用更快的GPU实现。目前开源的框架(💏)大多都支持(➕)GPU,如伯克利大学Caffe和Google Convnet。
微软在2015年2月宣布(💣)使用Stratix V完成了CNN加速器,处理 CIFAR10 图片速度可达每秒2300多张。
这(⛓)里我们也使用CIFAR10图片数据,在Cyclone V板子上跑一个卷积神经网络CNN demo。由于板子上计算资源太少(DSP Slice只有80多个),实现完整的网络不太现(🚤)实,只能在FPGA上实现基本计算单元,然后由HPS统一调度。性(🚍)能预期不会太高,后面给出。
CIFAR10图片都是什么呢?先来张图!
有兴趣的朋友可以到官网下(🚬)载(CIFAR10官网)。上面提到过,CNN是有监督学习系统,需要(🏕)大量带label的数据,CIFAR10就是这样一个开放的(⏰)数据(🙈)库,提供了60000张不同类别的图片,分为10个(🎁)类(如上图左侧所示),每个类别有600张图。这个数据集不算特别大,适合在嵌入式平台上实现。而更大的数据集有ImageNet-1000(ImageNet官网),拥有120多万张高清无码大图,我下载到硬盘,占用了近200GB空间(只能忍痛将其他rmvb和avi删掉了)!
有朋友会问,不用这些(❣)数据行不行,我们的智能手机里面照片能不能用于CNN做训练?
答案是可以的,只是(🆕)你的数据集很不“均匀”,采样不够“完备”,训练出的模型是真实(💛)模型的“有偏估计”,而上述两个数据集经过了种种考验,已经是学术界公认(🌍)的优质数据集,一年一度的ILSVRC比赛就采用了这些数据集。
说完数据,再说模(🧢)型。先来看一张经典的CNN结构:
这是世界上第一个将CNN实用化的例子,实现了手写体字母(⏲)自动识别。在这个CNN模型中,可以看到输入是一张32 x 32的二维图像,经过卷积层(Convolution)、下采样层(Subsampling,也称Pooling)、全连接层(Full Connection,也称Inner Product)后,得到一组概率密度,我们选其中概率最大的(🧓)元素作为该(🌚)模型对输(📤)入图像的分类结果。所(〽)以实现CNN时,只需要实现三种基本算法:卷积、下采样、矩阵(🍖)乘。除(➗)此之(🐇)外,每层(🔙)输出都可选择是否经过非线性变换,常用的非(🥪)线性变(🥥)换有ReLU和Sigmoid,前者(😷)计算较为简单,使用较为广泛。
Caffe框架中提供了专门为cifar10数据定制(🌆)的模型,是用proto格式写的,我们的demo也基于这个模型。内容如下:
name: "CIFAR10_quick_test"input: "data"input_dim: 1input_dim: 3input_dim: 32input_dim: 32layers {name: "conv1"type: CONVOLUTIONbottom: "data"top: "conv1"blobs_lr: 1blobs_lr: 2convolution_param {num_output: 32pad: 2kernel_size: 5stride: 1}}layers {name: "pool1"type: POOLINGbottom: "conv1"top: "pool1"pooling_param {pool: MAXkernel_size: 3stride: 2}}layers {name: "relu1"type: RELUbottom: "pool1"top: "pool1"}layers {name: "conv2"type: CONVOLUTIONbottom: "pool1"top: "conv2"blobs_lr: 1blobs_lr: 2convolution_param {num_output: 32pad: 2kernel_size: 5stride: 1}}layers {name: "relu2"type: RELUbottom: "conv2"top: "conv2"}layers {name: "pool2"type: POOLINGbottom: "conv2"top: "pool2"pooling_param {pool: AVEkernel_size: 3stride: 2}}layers {name: "conv3"type: CONVOLUTIONbottom: "pool2"top: "conv3"blobs_lr: 1blobs_lr: 2convolution_param {num_output: 64pad: 2kernel_size: 5stride: 1}}layers {name: "relu3"type: RELUbottom: "conv3"top: "conv3"}layers {name: "pool3"type: POOLINGbottom: "conv3"top: "pool3"pooling_param {pool: AVEkernel_size: 3stride: 2}}layers {name: "ip1"type: INNER_PRODUCTbottom: "pool3"top: "ip1"blobs_lr: 1blobs_lr: 2inner_product_param {num_output: 64}}layers {name: "ip2"type: INNER_PRODUCTbottom: "ip1"top: "ip2"blobs_lr: 1blobs_lr: 2inner_product_param {num_output: 10}}layers {name: "prob"type: SOFTMAXbottom: "ip2"top: "prob"}复制代码
可见,上述模型经过了3个卷积层(conv1, conv2, conv3),每个卷积层后面都跟着下采样层((🏜)pool1, pool2, pool3),之后有两个全连接层(ip1, ip2),最后一层prob为SOFTMAX分类层(🔪),是计算概率密度的,这里我们不需要关(🗃)心。
下面三张图分别统计了CNN模型(👭)各层的参数量、(🌧)数据量(💱)和(🖍)计算量。
可以看(👮)出,卷积层的参数量很少,但数据量很大;全连接层刚好相反,参数量较大,但数据量很少。
通过计算(🕒)量统计发现conv2计算量最大,其次是conv3和conv1。全连接层的计算量相对卷积层较小,但不可忽略。其他层(pool1, pool2以及各级relu)由于计算量太小(🖇),本设计中没有将其实现为Open CL kernel,而是直接CPU端实现。
综上所述,我们重点实现两个算法:卷积和矩阵乘,分别对应卷积层、全连接层(🔵)的实现。
在DE1-SOC上我利用了友晶提供的Open CL BSP,支持C语言开发FPGA。
卷积层计算kernel函数如下:
__attribute__((num_compute_units(4)))__kernelvoid conv(__global float * a, __global float * b, __global float * c, const int M, const int N, const int K){int gx = get_global_id(0);int gy = get_global_id(1);float tmp=0.0f;for(int x = 0; x < K; x ++){for(int y = 0; y < K; y ++){tmp += a[(gx + x) * M + (gy + y)] * b[x * K + y];}}复制代码
全连接层计算(🗨)采用矩阵乘实现,kernel函数如下:
__attribute__((num_compute_units(4)))__kernelvoid gemm(__global float * a, __global float * b, __global float * c, const int M, const int N, const int K){int gx = get_global_id(0);int gy = get_global_id(1);int sy = get_global_size(1);int sx = get_global_size(0);int s = sx * sy;for(int x = gx; x < M; x += sx){for(int y = gy; y < N; y += sy){float tmp=0.0f;for(int z = 0; z < K; z++){tmp += a[z * M + x] * b[y * K + z];}c[y * M + x] = tmp;}}}复制代码
编译kernel函数需要使用Altera SDK for OpenCL,我用的版本是14.0.0.200,申请了两个月的license。编译使用命令行aoc,得到*.aocx文件。
Open CL编译输出报告中给出了资源占用情况:
+--------------------------------------------------------------------+; Estimated Resource Usage Summary ;+----------------------------------------+---------------------------+; Resource + Usage ;+----------------------------------------+---------------------------+; Logic utilization ; 83% ;; Dedicated logic registers ; 46% ;; Memory blocks ; 57% ;; DSP blocks ; 25% ;+----------------------------------------+---------------------------;复制代码
可见,逻辑资源、(🕉)存储器资源消耗较为明显,而DSP资源并未用尽,说明还有优化的空间。
编译主程序需要使用SoCEDS,我用的版本为14.0.2.274,也(😒)是命令行方式,在工程目录下执行make,结束后得到可执行文件cnn。
将这两个文件拷贝到SD卡,按照前面的博客对板子进行设置,将CNN的模型、CIFAR10数据也拷贝到SD卡中,板子上电(🎷),mount SD卡到/mnt,执行cnn,得到输出如下:
<div class="blockcode"><blockquote>Please input the number of images(1~100):100Loading data...OK!Constructing CNN...OK!Begin calculation...Elapsed Time = 141.861 s.Real Label = 3(cat), Calc Label = 3(cat), error count = 0Real Label = 8(ship), Calc Label = 8(ship), error count = 0Real Label = 8(ship), Calc Label = 8(ship), error count = 0Real Label = 0(airplane), Calc Label = 0(airplane), error count = 0Real Label = 6(frog), Calc Label = 6(frog), error count = 0Real Label = 6(frog), Calc Label = 6(frog), error count = 0Real Label = 1(automobile), Calc Label = 1(automobile), error count = 0Real Label = 6(frog), Calc Label = 6(frog), error count = 0Real Label = 3(cat), Calc Label = 3(cat), error count = 0Real Label = 1(automobile), Calc Label = 1(automobile), error count = 0Real Label = 0(airplane), Calc Label = 0(airplane), error count = 0Real Label = 9(truck), Calc Label = 9(truck), error count = 0Real Label = 5(dog), Calc Label = 5(dog), error count = 0Real Label = 7(horse), Calc Label = 7(horse), error count = 0Real Label = 9(truck), Calc Label = 9(truck), error count = 0Real Label = 8(ship), Calc Label = 8(ship), error count = 0Real Label = 5(dog), Calc Label = 5(dog), error count = 0Real Label = 7(horse), Calc Label = 7(horse), error count = 0Real Label = 8(ship), Calc Label = 8(ship), error count = 0Real Label = 6(frog), Calc Label = 6(frog), error count = 0Real Label = 7(horse), Calc Label = 7(horse), error count = 0Real Label = 0(airplane), Calc Label = 2(bird), error count = 1Real Label = 4(deer), Calc Label = 4(deer), error count = 1Real Label = 9(truck), Calc Label = 9(truck), error count = 1Real Label = 5(dog), Calc Label = 4(deer), error count = 2Real Label = 2(bird), Calc Label = 3(cat), error count = 3Real Label = 4(deer), Calc Label = 4(deer), error count = 3Real Label = 0(airplane), Calc Label = 0(airplane), error count = 3Real Label = 9(truck), Calc Label = 9(truck), error count = 3Real Label = 6(frog), Calc Label = 6(frog), error count = 3Real Label = 6(frog), Calc Label = 6(frog), error count = 3Real Label = 5(dog), Calc Label = 5(dog), error count = 3Real Label = 4(deer), Calc Label = 4(deer), error count = 3Real Label = 5(dog), Calc Label = 5(dog), error count = 3Real Label = 9(truck), Calc Label = 9(truck), error count = 3Real Label = 2(bird), Calc Label = 3(cat), error count = 4Real Label = 4(deer), Calc Label = 7(horse), error count = 5Real Label = 1(automobile), Calc Label = 9(truck), error count = 6Real Label = 9(truck), Calc Label = 9(truck), error count = 6Real Label = 5(dog), Calc Label = 5(dog), error count = 6Real Label = 4(deer), Calc Label = 4(deer), error count = 6Real Label = 6(frog), Calc Label = 6(frog), error count = 6Real Label = 5(dog), Calc Label = 5(dog), error count = 6Real Label = 6(frog), Calc Label = 6(frog), error count = 6Real Label = 0(airplane), Calc Label = 0(airplane), error count = 6Real Label = 9(truck), Calc Label = 9(truck), error count = 6Real Label = 3(cat), Calc Label = 5(dog), error count = 7Real Label = 9(truck), Calc Label = 9(truck), error count = 7Real Label = 7(horse), Calc Label = 7(horse), error count = 7Real Label = 6(frog), Calc Label = 6(frog), error count = 7Real Label = 9(truck), Calc Label = 9(truck), error count = 7Real Label = 8(ship), Calc Label = 8(ship), error count = 7Real Label = 0(airplane), Calc Label = 2(bird), error count = 8Real Label = 3(cat), Calc Label = 3(cat), error count = 8Real Label = 8(ship), Calc Label = 8(ship), error count = 8Real Label = 8(ship), Calc Label = 8(ship), error count = 8Real Label = 7(horse), Calc Label = 7(horse), error count = 8Real Label = 7(horse), Calc Label = 7(horse), error count = 8Real Label = 4(deer), Calc Label = 3(cat), error count = 9Real Label = 6(frog), Calc Label = 3(cat), error count = 10Real Label = 7(horse), Calc Label = 7(horse), error count = 10Real Label = 3(cat), Calc Label = 5(dog), error count = 11Real Label = 6(frog), Calc Label = 6(frog), error count = 11Real Label = 3(cat), Calc Label = 3(cat), error count = 11Real Label = 6(frog), Calc Label = 6(frog), error count = 11Real Label = 2(bird), Calc Label = 2(bird), error count = 11Real Label = 1(automobile), Calc Label = 1(automobile), error count = 11Real Label = 2(bird), Calc Label = 2(bird), error count = 11Real Label = 3(cat), Calc Label = 3(cat), error count = 11Real Label = 7(horse), Calc Label = 9(truck), error count = 12Real Label = 2(bird), Calc Label = 2(bird), error count = 12Real Label = 6(frog), Calc Label = 6(frog), error count = 12Real Label = 8(ship), Calc Label = 8(ship), error count = 12Real Label = 8(ship), Calc Label = 8(ship), error count = 12Real Label = 0(airplane), Calc Label = 0(airplane), error count = 12Real Label = 2(bird), Calc Label = 2(bird), error count = 12Real Label = 9(truck), Calc Label = 0(airplane), error count = 13Real Label = 3(cat), Calc Label = 3(cat), error count = 13Real Label = 3(cat), Calc Label = 2(bird), error count = 14Real Label = 8(ship), Calc Label = 8(ship), error count = 14Real Label = 8(ship), Calc Label = 8(ship), error count = 14Real Label = 1(automobile), Calc Label = 1(automobile), error count = 14Real Label = 1(automobile), Calc Label = 1(automobile), error count = 14Real Label = 7(horse), Calc Label = 7(horse), error count = 14Real Label = 2(bird), Calc Label = 2(bird), error count = 14Real Label = 5(dog), Calc Label = 7(horse), error count = 15Real Label = 2(bird), Calc Label = 2(bird), error count = 15Real Label = 7(horse), Calc Label = 7(horse), error count = 15Real Label = 8(ship), Calc Label = 8(ship), error count = 15Real Label = 9(truck), Calc Label = 9(truck), error count = 15Real Label = 0(airplane), Calc Label = 0(airplane), error count = 15Real Label = 3(cat), Calc Label = 4(deer), error count = 16Real Label = 8(ship), Calc Label = 8(ship), error count = 16Real Label = 6(frog), Calc Label = 6(frog), error count = 16Real Label = 4(deer), Calc Label = 4(deer), error count = 16Real Label = 6(frog), Calc Label = 6(frog), error count = 16Real Label = 6(frog), Calc Label = 6(frog), error count = 16Real Label = 0(airplane), Calc Label = 2(bird), error count = 17Real Label = 0(airplane), Calc Label = 0(airplane), error count = 17Real Label = 7(horse), Calc Label = 7(horse), error count = 17Classify Score = 83 %.上面的执行流程是这样的,首先输入测试(📦)样本数目(1到100),由于DE1板子FPGA端SDRAM容量较小,难以加载全部测试数据(10000张图片),故每次最多装(🕌)入100张图片。之后载入数据到HPS内存,然后开(♿)始构建CNN模型(🥛),构建过程中也实现(🔋)了Open CL的初始化。构建完毕,将输入图像依次通过CNN,得到一系列分类结果(🛎),与标签进行对比,统(🔎)计错(📇)误分类个数,计算分类准确率。
经过测试,分类准确率达到83%,与Caffe测试结果一致。
经过(🙄)以上测试,可(🔡)以得到结(🦐)论:
(1)使用(🍢)Open CL可以很方便地移植高级语言编写的算法;
(2)CNN在移植过程中需要考虑实际硬件,定制合适的模型和数据;
(3)Cyclone 5逻辑资源较少(85K,Open CL kernel占用了83%),如果希望进一步提高计算速度,一方面(📡)可以选用高(🔁)性(🐥)能器件(如Stratix V、Arria 10),另一方面可以使用RTL自己搭建计算系统。
以上图文内容均是EEWORLD论坛网友zhaoyongke原创,在此感谢。
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