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Adventurer
Adventurer
10,203 Views
Registered: ‎02-08-2016

Use RAMB18 for Block Memory in Zynq device (Block memory Generator)

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Hi I am using Block Design editor to build a design using BRAM - I use the Block Memory Generator (BMG version 8.3) to build AXI interface Block RAM. The Cutomize option form allows me to specify various  params.

 

Here is the synthesis utilisation report. it clearly show the tool has built my RAMs using RAMB36 cells.

Device :  xc7z035ffg676-2

Tools : Vivado 2015.3

 

2. Memory
---------

+-------------------+-------+-------+-----------+-------+
|     Site Type     |  Used | Fixed | Available | Util% |
+-------------------+-------+-------+-----------+-------+
| Block RAM Tile    | 340.5 |     0 |       500 | 68.10 |
|   RAMB36/FIFO*    |   337 |     0 |       500 | 67.40 |
|     RAMB36E1 only |   337 |       |           |       |
|   RAMB18          |     7 |     0 |      1000 |  0.70 |
|     RAMB18E1 only |     7 |       |           |       |
+-------------------+-------+-------+-----------+-------+

 

I want to double the block ram size in the design.

 

However I cannot make the Block RAM generator utilize the RAMB18 cells. All Block RAMs are built by the tool from the RAMB36 cells. I note the following question below suggests that the RAMB18 and RAMB36 are one and the same ( aliased onto the same block ram resource) except the evidence seems to suggest this is not the case.

 

Community Forum Question :   "Use RAMB18 for Block Memory"

 

Please see attached pictures. Columns containing Block RAM are purple and green. The occupied cells are purple/blue. Empty Block RAMB18 cells can be clearly seen in the second fourth sixth etc. columns.

 

I have read the PG805 Block memory Generator Guide and this seems to suggest that I should be able to change the "Algorithm" option in the customization form for the Block memory Generator. This option is greyed out and locked. I have also tried using tcl commands and hacking the .xml file for my design. I still cannot coerce the tools to use the RAMB18 resource.

 

Do you have any suggestions.

 

Thanks

 

                Simon Hildebrand

 

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BLOCKRAM.png
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1 Solution

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Moderator
Moderator
19,589 Views
Registered: ‎07-01-2015

Re: Use RAMB18 for Block Memory in Zynq device (Block memory Generator)

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Hi @simonh_bwt,

 

Your device has 500RAMB36 , it means either you can use 500RAMB36 or 1000RAMB18 or mix and match.

2RAMB18 can sit in one RAMB36 site. As your utilization is already 68.10% you can't double number of BRAMs.

 

If you want you can use distributed RAM.

 

Thanks,
Arpan

Thanks,
Arpan
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2 Replies
Moderator
Moderator
19,590 Views
Registered: ‎07-01-2015

Re: Use RAMB18 for Block Memory in Zynq device (Block memory Generator)

Jump to solution

Hi @simonh_bwt,

 

Your device has 500RAMB36 , it means either you can use 500RAMB36 or 1000RAMB18 or mix and match.

2RAMB18 can sit in one RAMB36 site. As your utilization is already 68.10% you can't double number of BRAMs.

 

If you want you can use distributed RAM.

 

Thanks,
Arpan

Thanks,
Arpan
----------------------------------------------------------------------------------------------
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Give Kudos to a post which you think is helpful and reply oriented.
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Scholar u4223374
Scholar
10,197 Views
Registered: ‎04-26-2015

Re: Use RAMB18 for Block Memory in Zynq device (Block memory Generator)

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I note the following question below suggests that the RAMB18 and RAMB36 are one and the same ( aliased onto the same block ram resource) except the evidence seems to suggest this is not the case.

 

What evidence would that be? It is the case. UG473 explains the memory architecture in detail.

 

The Zynq 7035 has 500 RAMB36s, which can alternatively be used as 1000 RAMB18s. These are physically the same hardware, just wired up in different ways depending on what mode is in use. You will have to either move to a larger chip (the Zynq Ultrascales have massive amounts of on-chip RAM) or find a more efficient way of storing data.

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