基于FPGA的mif文件创建与使用

基于FPGA的mif文件创建与使用

　1 引言


　　在一些需要特殊运算的应用电路中，只读存储器ROM是关键元件，设计人员通常利用ROM创建各种查找表，从而简化电路设计，提高电路的处理速度和稳定性。FPGA是基于SRAM的可编程器件。掉电后FPGA上的配置信息将全部丢失，所以由FPGA构造的数字系统在每次上电后要依赖于外部存储器来主动配置或在线被动配置。真正意义上的ROM应具有掉电后信息不丢失的特性，因此利用FPGA实现的ROM只能认为器件处于用户状态时具备ROM功能。使用时不必要刻意划分，而ROM单元的初始化则是设计人员必须面对的问题。本文讨论FPGA的ROM初始化问题，详细介绍mit文件的创建与使用。

　　2 基于FPGA的ROM的实现


　　基于MAX+PLUSⅡ软件平台，FPGA可编程器件实现ROM功能比较简单。只需运行MAX+PLUSⅡ，选择图形输入，在新建页的空白处双击并在弹出的对话框中选择d：＼maxplus2＼max2lib＼mega_lpm，调用软件提供的参数可调库(mega_lpm)，找出参数化ROM宏模块(lpm_rom)，如图1所示。表1列出lpm_ROM宏模块的端口及参数设置。


　　根据需要选择必要的Address[]、q[]两个端口创建加法运算的查找表。引入lpm_ROM宏模块后，一定要把LPM_ADDRESS_CONTROL设置为″UNREGISTERED″，否则编译报错。本系统设计选用了Altera公司的FLEX10K系列的FPGA(EPF10K10LC84-4)，其模块结构如图2所示。

　　引入lpm_ROM宏模块后，开始ROM的初始化，这是运用lpm_ROM宏模块做为系统开发的关键。ROM初始化就是要在对应的地址赋初始值以实现查找表的功能。在系统编译之前一定要先设置LPM_FILE参数。实际上就是要加入一个mif文件或hex文件。以下详细讨论在MAX+PLUSⅡ环境下mif文件的创建和使用。

　　3 lpm_ROM初始化及mif文件

　　3.1 mif文件的格式及创建

　　3.1.1 mif文件格式

　　mif文件是在编译和仿真过程中作为存储器(ROM或RAM)初始化输入的文件，即memory initialization file。mif文件格式为：


　　3.1.2 mif文件创建


　　mif文件的创建很简单，主要有两种方法，一种是在MAX+PLUSⅡ环境下，新建文件，选文本输入，保存为mif文件。另一种方法是建立一个txt文件，然后将扩展名改成mif即可。

　　3.2 mif文件的使用


　　依上述方法创建的mif文件只是一个空文件，在lpm_ROM宏模块的LPM_FILE中引入这样的文件，仅仅能帮助lpm_ROM宏模块通过编译并把所有的存储单元初始化为零。且在编译出现：Warning：Can't find data in initial memory content[MIF／HEX]file。

　　mif文件的格式是固定的，对于前4行(DEPTH，WIDTH，ADDRESS_RADIX，DATA_RADIX)，前2个参数应与lpm_ROM宏模块LPM_WIDTHAD和LPM_WIDTH相关联，后2个参数为了方便一般设置为DEC(十进制)。关键是文件内容的begin与end之间的部分。mif文件的使用就是修改begin与end之间的内容。主要有两种修改方法。

基于FPGA的mif文件创建与使用

基于FPGA的mif文件创建与使用

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把这个保存成hex文件即可，得到一个