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FPGA LZMA compressor

An FPGA-based LZMA compressor. For generic lossless data compression.

☁️ LZMA is a popular data compression algorithm, which is defaultly use by ".7z" and ".xz" format. It is also available in ".zip" format.

👍 LZMA usually has better compression ratio than DEFLATE and BZIP algorithm.

　

Features:

• Pure RTL design , universal for all FPGA platforms.
• Simple streaming input/output : input raw data stream, output compressed LZMA stream.
• LZMA dictionary size: 131072 bytes. The hash search engine support 4096 hash values × 8 hash entries.
• High compression ratio (see Evaluation of compression ratio)
• FPGA resource :
  • use 2275 LUTs and 55 BRAM36K on Xilinx 7 series
  • use 3484 LUTs and 1.8 Mbits BRAM on Altera Cyclone IV.
• Performance：
  • 118 MHz on the slowest speed-level device of Xilinx Artix7 (e.g. xc7a100tcsg324-1)
  • 250 MHz on the slowest speed-level device of Xilinx Zynq Ultrascale+ (e.g. xczu3eg-sbva484-1-e)
  • 83 MHz on the slowest speed-level device of Altera Cyclone IV E (e.g. EP4CE115F23C8)
  • 13 cycles to consume a input byte on average.

For current version, the compression ratio and FPGA resource are good enough, but the performance doesn't satisfy me (only similar to single-threaded compression on personal computers). Therefore, the current version may only be usefual for some embedded applications. I will optimize its performance in the future.

　

Evaluation of compression ratio

We use a 512KB data as input to compare several compressors, the result is as follows:

Compressor	Compress algorithm	Compress level	Compressed size
do not compress	-	-	512 KB
7ZIP software	GZIP, ".gz" format, DEFLATE algorithm	fast	287 KB
7ZIP software	GZIP, ".gz" format, DEFLATE algorithm	standard	281 KB
7ZIP software	GZIP, ".gz" format, DEFLATE algorithm	extreme	260 KB
7ZIP software	XZ, ".xz" format, LZMA2 algorithm	fast	262 KB
7ZIP software	XZ, ".xz" format, LZMA2 algorithm	standard	249 KB
7ZIP software	XZ, ".xz" format, LZMA2 algorithm	extreme	248 KB
FPGA-GZIP-compressor	GZIP, ".gz" format, DEFLATE algorithm	-	299 KB
FPGA-LZMA-compressor (this)	".lzma format", LZMA algorithm	-	255 KB

　

　

Module Usage

The design source code is in RTL directory. In which lzma_compressor_top.v is the top module.

Module in/out signals

The in/out signals of lzma_compressor_top.v are:

module lzma_compressor_top (
    input  wire        rstn,
    input  wire        clk,
    // input : raw data stream
    output wire        i_ready,
    input  wire        i_valid,
    input  wire        i_last,
    input  wire [ 7:0] i_data,
    // output : LZMA stream  // Note! need to add an additional 13-byte fixed header before the output stream to make up a complete "LZMA" file format. The 13 bytes are : {0x5E, 0x00, 0x00, 0x02, 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF}
    output wire        o_valid,
    output wire [ 7:0] o_data,
    output wire        o_last    // end of a LZMA stream
);

　

Reset

• reset when rstn=0
• On most FPGAs, it can actually work without resetting. On some FPGAs that do not support initial register, it is necessary to reset before use.

　

Input stream

The input interface is a standard 8-bit wide AXI-stream slave interface. We use it to input the data to be compressed.

• i_valid handshakes with i_ready . Successfully input 1 data only when i_valid=1 and i_ready=1 simultaneously (see following figure).
• i_data is one-byte input data.
• i_last is the boundary mark of the package, i_last=1 means that the current byte is the last byte of a packet, and the next transmitted byte is the first byte of the next packet. Each packet is compressed into an independent LZMA stream.

             _    __    __    __    __    __    __    __    __    __    __    __
    clk       \__/  \__/  \__/  \__/  \__/  \__/  \__/  \__/  \__/  \__/  \__/  \
                         _____________________________             _____
  i_valid    ___________/                             \___________/     \________
             _________________                   ________________________________
  i_ready                     \_________________/
                         _____ _______________________             _____
  i_data     XXXXXXXXXXXX__D1_X___________D2__________XXXXXXXXXXXXX__D3_XXXXXXXXX  

　

Output LZMA stream

The output interface is a simple 8-bit wide AXI-stream master interface without handshake.

• o_valid=1 means there's a valid output byte on o_data
• o_data is the data byte of compressed LZMA stream.
• o_last is the boundary mark of LZMA stream. When o_valid=1 and o_last=1 , the current byte is the last byte of a LZMA stream.
• When o_last=1 , o_valid must be 1 .

　

Add header for output LZMA stream

Each output stream is a independent LZMA stream, without any headers.

To let the output LZMA stream be recognized, we need to use "container formats" (i.e., add headers). Note that ".zip", ".xz", ".7z" are all container formats. (Here we do not introduce them).

A simpest way is to use the ".lzma" container format. Its format is simple:

".lzma" format = 13-byte header + LZMA stream

The 13-byte header is:

0x5E, 0x00, 0x00, 0x02, 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF

After this 13-byte header, we append the LZMA stream, i.e., the bytes outputted by my module.

We put all these bytes to a ".lzma" file, then the file can be recognized and decompressed by several LZMA softwares (see How to decompress the generated ".lzma" file for detail)

　

　

Simulation

The simulation source code is in SIM directory. In which tb_lzma_compressor.v is the top module.

The diagram of this testbench is as follows:

　

Among them, the random data packet generator (tb_random_data_source.v) will generate four types of data packets with different characteristics (random bytes with uniform distribution, random bytes with non-uniform distribution, randomly continuously changing data, and sparse data), which will be sent to the design under test (lzma_compressor_top) for compression.

tb_save_result_to_file.v module will store the compressed results into files. Each stream is stored into a independent .lzma file (it will also append the 13-byte header).

　

Simulate using iverilog

You can follow the following steps to simulate using iverilog:

• Install iverilog, see iverilog_usage
• In Windows, double click tb_lzma_compressor_run_iverilog.bat to run simulation. Where tb_lzma_compressor_run_iverilog.bat contains the simulation compilation and running commands.
• When simulation, the random packet generator will generate 20 packets by default, the simulation usually takes about one hour to complete. You can modify the macro FILE_COUNT in tb_random_data_source.v .
• The generated compressed LZMA data will be stored in sim_data directory as ".lzma" file.

　

Simulate using other simulators

Besides iverilog, you can also use other simulators. Just add all the .v files in RTL and SIM directories to the simulation project, and set tb_lzma_compressor.v to be the top-level file for simulation.

　

How to decompress the generated ".lzma" file

The data of the ".lzma" file is composed of a 13-byte header and LZMA compressed stream. Here we introduce how to use software to decompress ".lzma" file.

on Windows

On Windows, you can use the official 7ZIP/LZMA software to decompress the generated ".lzma" file. To get it, download the "LZMA SDK", extract it. In the "bin" directory, you can see "lzma.exe".

I've put the executable file "lzma.exe" into SIM directory.

To decompress a ".lzma" file, open CMD in SIM directory, and run command as format:

.\lzma.exe d [input_lzma_file] [output_file]

For example, run following command to decompress "sim_data\out001.hex.lzma" into "out001.hex":

.\lzma.exe d sim_data\out001.hex.lzma out001.hex

on Linux

On Linux, you can decompress ".lzma" file using the official "p7zip" software. You should firstly install it:

apt-get install p7zip

Then use following command to decompress the ".lzma" file.

7z x [input_lzma_file]

For example, the following command can decompress "sim_data/out001.hex.lzma".

7z x sim_data/out001.hex.lzma

The decompressed file will be "sim_data/out001.hex"

It may report a error : "ERROR: There are some data after the end of the payload data" . Just ignore it, because there may be a extra "0x00" at the end of ".lzma" file. It won't affect the normal data decompression.

　

　

See Also

The official code and document of LZMA & 7ZIP:

• [1] https://www.7-zip.org/sdk.html

To quickly understand the algorithm of LZMA, see:

• [2] wikipedia : https://en.wikipedia.org/wiki/Lempel%E2%80%93Ziv%E2%80%93Markov_chain_algorithm
• [3] A minimal LZMA data compressor & decompressor. Only hundreds of lines of C : https://github.com/WangXuan95/TinyLZMA

Other FPGA-based data compressors (based on GZIP/DEFLATE algorithm, the compression ratio is not better than LZMA):

• [4] FPGA-Gzip-compressor : https://github.com/WangXuan95/FPGA-Gzip-compressor
• [5] HDL-deflate : https://github.com/tomtor/HDL-deflate

　

　

　

　

　

　

FPGA LZMA compressor

一个基于 FPGA 的 LZMA 压缩器，用于通用数据压缩

☁️ LZMA 是一种常用的数据压缩算法。".7z" 和 ".xz" 格式默认使用的算法是 LZMA。".zip" 格式也支持 LZMA 算法。

👍 LZMA 的压缩率通常高于 GZIP/DEFLATE 和 BZIP

　

技术特点：

• 纯 RTL 设计，适用于各种 FPGA 平台。
• 极简的流式输入/输出接口 ，输入待压缩数据，输出LZMA压缩流。
• LZMA 字典大小: 131072 字节。哈希匹配搜索引擎包含 4096个哈希值 × 8个哈希entry
• 高压缩率 (详见 压缩率评估)
• FPGA 资源占用 :
  • 在 Xilinx 7 系列上占 2275 LUTs 和 55 BRAM36K
  • 在 Altera Cyclone IV 系列上占 3484 LUTs and 1.8 Mbits BRAM
• 性能：
  • 平均输入一个字节需要 13 周期
  • 在 Xilinx Artix7 的速度最慢的FPGA (-1 速率级别) 上达到 118 MHz ，平均性能约为 118/13 = 9MB/s
  • 在 Xilinx Zynq Ultrascale+ 的速度最慢的FPGA (-1 速率级别) 上达到 250 MHz ，平均性能约为 250/13 = 19MB/s
  • 在 Altera Cyclone IV E 的速度最慢的FPGA (8 速率级别) 上达到 83 MHz ，平均性能约为 83/13 = 6.3MB/s

当前版本的压缩率和FPGA资源消耗都足够好，但性能还不够让我满意 (7ZIP的LZMA快速压缩在个人计算机上使用单线程，性能约为约为5~10MB/s)。因此，当前版本可能仅适用于某些嵌入式应用。我将来会优化它的性能。

　

压缩率评估

我使用一个 512KB data 作为待压缩数据，比较该压缩器与其它压缩方案，结果见下表。

压缩器	压缩算法	压缩级别	压缩后大小
do not compress	-	-	512 KB
7ZIP 软件	GZIP, ".gz" 格式, DEFLATE 算法	极速压缩	287 KB
7ZIP 软件	GZIP, ".gz" 格式, DEFLATE 算法	标准压缩	281 KB
7ZIP 软件	GZIP, ".gz" 格式, DEFLATE 算法	极限压缩	260 KB
7ZIP 软件	XZ, ".xz" 格式, LZMA2 算法	快速压缩	262 KB
7ZIP 软件	XZ, ".xz" 格式, LZMA2 算法	标准压缩	249 KB
7ZIP 软件	XZ, ".xz" 格式, LZMA2 算法	极限压缩	248 KB
FPGA-GZIP-compressor	GZIP, ".gz" 格式, DEFLATE 算法	-	299 KB
FPGA-LZMA-compressor (本设计)	".lzma 格式", LZMA 算法	-	255 KB

　

　

模块使用方法

设计代码在 RTL 目录中. 其中 lzma_compressor_top.v 是顶层模块。

模块输入/输出信号

module lzma_compressor_top (
    input  wire        rstn,
    input  wire        clk,
    // input : raw data stream
    output wire        i_ready,
    input  wire        i_valid,
    input  wire        i_last,
    input  wire [ 7:0] i_data,
    // output : LZMA stream  // Note! need to add an additional 13-byte fixed header before the output stream to make up a complete "LZMA" file format. The 13 bytes are : {0x5E, 0x00, 0x00, 0x02, 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF}
    output wire        o_valid,
    output wire [ 7:0] o_data,
    output wire        o_last    // end of a LZMA stream
);

　

复位

• 当 rstn=0 时，模块复位
• 在大多数 FPGA 上其实可以不用复位就能工作。在少数不支持 initial 寄存器初始化的 FPGA 上，使用前必须复位。

　

输入接口

输入接口是标准的 8-bit 位宽的 AXI-stream slave，用来输入待压缩数据

• 所有信号都在 clk 的上升沿改变或被采样
• i_valid 和 i_ready 构成握手信号，只有同时=1时才成功输入了1个数据 (如下图)。
• i_data 是1字节的输入数据。
• i_last 是包 (AXI-packet) 的分界标志。当 i_valid=1 时，i_tlast=1 意味着当前传输的是一个包的末尾字节，而下一个传输的字节就是下一包的首字节。每个包会被压缩为一个独立的 LZMA 压缩流。

             _    __    __    __    __    __    __    __    __    __    __    __
    clk       \__/  \__/  \__/  \__/  \__/  \__/  \__/  \__/  \__/  \__/  \__/  \
                         _____________________________             _____
  i_valid    ___________/                             \___________/     \________
             _________________                   ________________________________
  i_ready                     \_________________/
                         _____ _______________________             _____
  i_data     XXXXXXXXXXXX__D1_X___________D2__________XXXXXXXXXXXXX__D3_XXXXXXXXX  

　

输出接口

输出接口是精简的、无握手的、8-bit 位宽的 AXI-stream master ，用来输出 LZMA 压缩流。

• 所有信号都在 clk 的上升沿改变或被采样
• o_valid=1 时， o_data 有效。
• o_data 是输出的 LZMA 压缩流中的一个字节。
• o_last 用来界定 LZMA 压缩流的边界。当 o_valid=1 且 o_last=1 ，说明当前字节是一个LZMA压缩流的最后一个字节。
• 当 o_last=1 时，一定有 o_valid=1

　

为输出LZMA压缩流添加文件头

每个输出的 LZMA 压缩流都是独立的，不带任何文件头。

为了让输出的LZMA流被各种解压软件识别，我们需要使用“容器格式”（即添加文件头或文件尾）。注意，“.zip”、“.xz”、“.7z” 都是容器格式。它们比较复杂，这里我们不介绍它们。

这里只介绍一种非常简单的容器格式 ： ".lzma" 格式。它的格式是：

.lzma" 格式 = 13字节文件头 + LZMA压缩流

其中，13字节文件头是固定的：

0x5E, 0x00, 0x00, 0x02, 0x00, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF

当我们将完整的 ".lzma" 格式的数据 (13字节文件头+LZMA压缩流) 保存到 ".lzma" 文件后，就可以用各种官方压缩软件来解压它，详见 如何解压 ".lzma" 文件 。

　

　

仿真

仿真相关的文件都在 SIM 目录里。其中 tb_lzma_compressor.v 是 testbench 的顶层。

testbench 的框图如下：

　

其中，随机数据包生成器 (tb_random_data_source.v) 将生成四种不同特征的数据包 (均匀分布的随机字节、非均匀分布的随意字节、随机连续变化的数据和稀疏数据) ，这些数据包将被发送到待测设计 (lzma_compressor_top) 进行压缩。

tb_save_result_to_file.v 模块将压缩后的结果存储到文件。每个 LZMA压缩流都会存储在一个独立的 ".lzma" 文件中 (该模块也负责附加13字节的文件头)。

　

使用 iverilog 仿真

你可以按照以下步骤进行 iverilog 仿真：

• 需要先安装 iverilog ，见教程：iverilog_usage 。
• 然后直接双击 tb_lzma_compressor_run_iverilog.bat 文件就能运行仿真 (仅限Windows) 。tb_lzma_compressor_run_iverilog.bat 包含了执行 iverilog 仿真的命令。
• 随机数据包生成器默认会生成 20 个数据包，每个数据包都会被压缩为一个 LZMA 压缩流。你可以通过修改 tb_random_data_source.v 里的宏名 FILE_COUNT 来修改数量。在20个文件的情况下，仿真一般要运行一小时才能结束。
• 仿真生成的 LZMA 压缩流会存放于 sim_data 目录 ，你可以通过修改 tb_save_result_to_file.v 里的宏名 OUT_FILE_PATH 来修改存放的目录。

　

使用其它仿真器

除了 iverilog ，你也可以用其它仿真器来仿真。只需要把 RTL 和 SIM 目录里的所有 .v 文件加入仿真工程，并以 tb_lzma_compressor.v 为仿真顶层进行仿真即可。另外，请注意 tb_save_result_to_file.v 里使用了相对路径来保存输出的 ".lzma" 文件，这会导致一些仿真器找不到正确的路径，因此你可能需要把它改成绝对路径。

　

如何解压 ".lzma" 文件

".lzma"文件的数据是由 13bytes 的文件头 + LZMA压缩流 构成的。下面介绍如何用软件解压 ".lzma"文件。

Windows

在 Windows 系统上，你可以使用 7ZIP/LZMA官方软件 来解压 ".lzma" 文件。获取方法：下载并解压 "LZMA SDK"。在 "bin" 目录中找到 "lzma.exe" 。

我已经将 "lzma.exe" 放入 SIM 目录。

要解压 ".lzma" 文件，请在 CMD 中运行如下格式的命令：

.\lzma.exe d [输入".lzma"文件] [输出文件]

例如，如下命令可以把 "sim_data\out001.hex.lzma" 解压为 "out001.hex" ：

.\lzma.exe d sim_data\out001.hex.lzma out001.hex

Linux

在 Linux 系统上，你可以使用 "p7zip" 软件来解压 ".lzma" 文件。

首先，运行以下命令来安装：

apt-get install p7zip

要解压 ".lzma" 文件，请运行如下格式的命令：

7z x [输入".lzma"文件]

例如，如下命令可以解压 "sim_data/out001.hex.lzma"

7z x sim_data/out001.hex.lzma

解压缩后的文件名为 "out001.hex"

它可能会报告："ERROR: There are some data after the end of the payload data"。不用管它，因为在".lzma"文件的末尾可能会有一个额外的"0x00"。它不会影响数据的正常解压。

　

　

参考链接

7ZIP/LZMA 官方代码和文档：

• [1] https://www.7-zip.org/sdk.html

以下资料可以帮你理解 LZMA 算法

• [2] wikipedia : https://en.wikipedia.org/wiki/Lempel%E2%80%93Ziv%E2%80%93Markov_chain_algorithm
• [3] 一个精简的LZMA压缩器/解压器，仅几百行C语言 : https://github.com/WangXuan95/TinyLZMA

其它开源的 FPGA 数据压缩器 (基于 GZIP/DEFLATE, 压缩率不及 LZMA)

• [4] FPGA-Gzip-compressor : https://github.com/WangXuan95/FPGA-Gzip-compressor
• [5] HDL-deflate : https://github.com/tomtor/HDL-deflate