FPGA专家教您如何在FPGA设计中使用HLS

Luke Miller并非一开始就是HLS（高层次综合）的倡导者。在使用早期的工具版本的时候，他似乎有过一些糟糕的经历。他写道： “……我的心筑起心墙，我需要帮助。”幸运的是，现在的他似乎已经通过了一个12步HLS培训活动， 现在可以利用Xilinx Vivado HLS有效地开展工作了。

SemiWiki 有了一位新的博主，被称为“The FPGA Expert（FPGA专家）”。通过LinkedIn简单搜索，我得知这位FPGA专家是Luke Miller，他最近发表了一篇博文，介绍如何使用高层次综合（HLS）开发从C到其他HLL版本的各种加速硬件。 虽然不像“手把手的菜谱”那样具体详尽，但依然非常有趣。

Miller曾经在IBM公司担任过ASIC设计师，在Lockheed担任过硬件师（工程师/架构师），目前是一位拥有军事和航空设计经验的PE。Miller的网站名为FPGA Expert，上面有一段特别的讲述其个人经历的视频，其中描述了多项军事、航空和医疗项目（飞机、雷达和医疗成像），所以，我猜他应该拥有非常丰富的FPGA设计经验。他的网站证实了这个猜想。 Miller似乎也非常了解HLS。他写道：

“设计时间的加速并非从C到VHDL的转换， 真正起到关键因素的是仿真域 —您再也无需通过RTL逐件验证每项设计。”
Luke Miller并非一直都是HLS（高层次综合）的倡导者。在使用早期的工具版本的时候，他似乎有些糟糕的经历。。他写道：“……我的心筑起心墙，我需要帮助。”幸运的是，他似乎已经通过了一个12步HLS培训活动， 现在可以通过Xilinx Vivado HLS有效地开展工作了。

点击此处，阅读Miller有关HLS的建议：“高层次综合 —它真的行！ （ High Level Synthesis – It’s for Real） ”%96-%92s-real.html

下面是Miller的全文供参考：

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High Level Synthesis – It’s for Real
by
theFPGAexpert
Published on 04-11-2013 06:30 PM

It was spring 2010 and I was asked to attend an HLS (High Level Synthesis) meeTIng. To be honest I cringed, after my bad relaTIonship with Accel DSP and broken promises my heart was all walled up and needed counseling. But my management had a way of making me an offer I could not refuse, like keeping my job. So reluctantly I went. Does your employer do lunch and learns instead of real training? You know what that equals right? A 1/8 pay cut, but let’s play nice.

Anyways after the usual introducTIons at the meeTIng they began to get into the meat of the tool. I quickly diverted and asked if we could see the tool in action and move away from the power point and boy did they. First up was a cookie cutter FIR filter but it worked, really! Then they moved into floating point designs etc. This HLS was the greatest thing since sliced bread. I saw its potential and I needed to try it. We all agreed on an evaluation period. Now I am by no means the best coder in the world, but even the best would have a hard time beating the HLS tool with respect to design time, area and latency.

What HLS is not: It is not a coder in a box, thus sit down the software guy and have him designing FPGAs. You need to understand the FPGA, no exceptions or you will have a fat, slow design. The C or its variant will need to be restructured, smartly, thus helping the tool out so it can perform better. It is not a button you press and you have a bit image. I know how program managers think.

I leverage HLS tools in this fashion. I view it as Xilinx Corgen on steroids which are driven by a C file. The speed up in design time is not in the translation from C to VHDL but really is in the simulation domain. You are no longer verifying designs piece by piece using RTL. For example, I design a Beamfomer in C. I compile it and then run ‘a.exe’ and verify that the answer matches the expects. That took about a second. For many PRIs of data that could of taken hours in ModelSim. Catching on? I then bring up the HLS tool and pull in the C file and the tool reports the latency, area, clock frequency etc. From that information I can determine which FPGA to use. I then start using directives to optimize the area / latency by using unrolls and pipeline directives. About an hour later my beamformer is done. I then simulate the RTL at my top level but I already know the math works and the tool took care of the boundary conditions. The goal of this article is by no means a recipe on HLS usage but hopefully entices you to check it out, you won’t be sorry.