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。

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