原创 如何利用altera 给出的megafunction配置成自己想要的FIFO和RAM

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在FPGA设计过程中，一般都要用到FIFO和RAM，如何利用altera 给出的megafunction配置成自己想要的FIFO和RAM，就得从自己的设计的RAM功能来看。主要考虑：端口数目、宽度和深度、时钟、时钟使能、读端口使能、输出端口是否寄存、复位（port、Widths and depths、Clks 、readen、Regs 、clkens、 Aclrs）。

这里强调下：
Asychronous Clear,只复位输入\输出端口的寄存器,不复位RAM块里的数据。对altera 的不同芯片,有的只复位输出寄存器,有的复位输入和输出寄存器。
还要注意:Write and Read Operations Triggering, 即读\写操作的时序,比如用M4K 的Memory Blocks作为RAM的话,下降沿写入数据,上升沿读出数据。
详细可以看:http://www.altera.com/literature/ug/ug_ram.pdf

下面就介绍几种常用的storage megafunction。

1.  altsyncram

Parameterized true dual-port synchronous RAM megafunction。

端口:可配置成：一端口读（或一端读、一端写；一端读、双端写；双端口读、双端口读写）的异步复位RAM。

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时钟:可配置成单一时钟、读\写双时钟、端口A\B双时钟。

2.  lpm_fifo _dc

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Parameterized dual-clock FIFO megafunction.

读数据端口：可配置成Legacy synchronour FIFO mode 和Show-ahead synchronous FIFO mode.

3.       lpm_fifo

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Parameterized single-clock FIFO megafunction.

4.  lpm_shiftreg

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Parameterized shift register megafunction. Altera recommends that you use the lpm_shiftreg function to replace all other types of shift register functions.

5.  lpm_tff

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Parameterized T-type flipflop megafunction. Altera recommends that you use lpm_ff rather than lpm_tff

下列的RAM megafunction，Altera 推荐用altsyncram

1.  Alt3pram :

Parameterized triple-port RAM megafunction.

2.        Altdpram

Parameterized dual-port RAM megafunction. This megafunction is provided only for backward compatibility in Cyclone, Cyclone II, HardCopy Stratix, Stratix, and Stratix GX designs; instead, Altera recommends using the altsyncram megafunction.

3.  csdpram Parameterized cycle-shared dual-port RAM megafunction. Altera recommends using lpm_ram_dp for dual-port RAM functions in ACEX 1K, APEX 20K, APEX II, FLEX 10KE, and Mercury projects.

4.       lpm_ram_dp

Parameterized dual-port RAM megafunction. This megafunction is provided only for backward compatibility in Cyclone, Cyclone II, HardCopy Stratix, Stratix, and Stratix GX designs; instead, Altera recommends using the altsyncram megafunction.

5.  lpm_ram_dq Parameterized RAM with separate input and output ports megafunction. Altera recommends using lpm_ram_dq to implement asynchronous memory or memory with synchronous inputs and/or outputs. This megafunction is provided only for backward compatibility in Cyclone, Cyclone II, HardCopy Stratix, Stratix, and Stratix GX designs; instead, Altera recommends using the altsyncram megafunction.

6.  lpm_ram_io Parameterized RAM with a single I/O port megafunction. This megafunction is provided only for backward compatibility in  Cyclone, Cyclone II, HardCopy Stratix, Stratix, and Stratix GX design; instead, Altera recommends using the altsyncram megafunction.

7.  pm_rom Megafunction  

Parameterized ROM megafunction. Altera recommends that you use the lpm_rom function to implement all ROM functions. This megafunction is provided only for backward compatibility for Cyclone, Cyclone II, HardCopy Stratix, Stratix, and Stratix GX  devices; instead, Altera recommends using the altsyncram megafunction.

下列的FIFO megafunction，Altera 推荐用lpm_fifo_dc

1.  csfifo Megafunction

Parameterized cycle-shared FIFO megafunction. Altera recommends that you use lpm_fifo instead of csfifo for single-clock FIFO functions, and that you use lpm_fifo_dc instead of csfifo for dual-clock FIFO functions.

2.  dcfifo Megafunction

Parameterized dual-clock FIFO megafunction

3.  scfifo Megafunction  

Parameterized single-clock FIFO megafunction.