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Altera_Forum
Honored Contributor I
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On Chip Memory Configuration and Altera Megafunction

Hi! I have a Cyclone V device that has 5,662,720 block memory bits.I have implemented 3 dual port RAMs that are 8 bits wide and 139520 deep.I figured that each RAM would amount to 109 M10K blocks, and I have tested the design in hardware and it seems to work.All three of these RAMs were inferred in code and no IP core was used. 

I have a few questions though : 

1) Why does the Altera Megafunction provide depth only in powers of 2 like 2048(2^11)... 32768(2^15) ... 65536(2^16)? 

Is it only so that the memory can be fully addressed by a n-bit pointer?  

2) Why doesn't it go beyond 65536? Especially when I can infer 3 dual port RAMs of 139520(not a power of 2) depth? 

3) How to know what sort of memory has been inferred? M10K, M4K, M9K? The megafunction GUI allows you to specify but I think there's no such provision possible when you try to infer it in code. 

 

By this point, the synthesis report shows that I am using 3,348,000/5,662,720 block memory bits (59 percent). 

 

Now, I tried to infer 6 single port RAMs 1 bit wide & 69120 deep.The design doesn't synthesize and gives the following warning : 

"cannot convert all sets of registers into ram megafunctions when creating nodes..." 

 

i get the warning despite having auto ram replacement turned on(by default). 

 

 

Strangely, when I try to infer the same amount of memory in a different configuration like 8 bits wide and 51840 deep, the design works. 

Why is this so? 

Which is a more efficient memory design? High depth or High Width? 

 

Thank you!
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Altera_Forum
Honored Contributor I
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See the "Recommended HDL Coding Styles" chapter in the Quartus handbook for details on all this. 

 

You can use synthesis attributes added to your HDL code to select a type of memory block to use. 

 

You don't display your code, but to infer RAMs, the inputs and outputs of the RAM must all be registered. 

 

Check your device's handbook and the Quartus handbook for specifics.
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