Here is new definition for keyword "if_2", version 2.

Here is new definition for keyword "if_2", version 2.
It is developed based on many discussions after my first post: " New keywor
d "if_2" is suggested for dealing with 2-write port memory."
New keyword "if_2" is used to put m-write and n-read memory module from chi
p manufactures' toolbox behind HDL language so that with the new keyword "i
f_2" introduction any m-write and n-read memory module would be fully speci
fied in HDL with very simple coding and without special technique and knowl
edge about memory module, or instantiated memory module needed for circuit
designers. All related complex job is left to synthesizer' manufacturers.
If_2-statement ::=
[ if_2_label : ]
if_2 condition then
sequence_of_statements
{ elsif condition then
sequence_of_statements }
[ else
sequence_of_statements ]
end if [ if_2_label ] ;
1. Any assignment statement's target array in sequence_of_statements under
an if-2 statement is an independent write to a memory that must be executed
, not obeying statement sequence in a process, regardless how many writes t
o the target array are coded before or after its appearance.
2. Any assignment statement's target non-array signal in sequence_of_statem
ents under an if_2 statement obeys statement sequence in a process.
3. An if-statement under an if_2-statement is treated as an if_2-statement.
4. An if_2-statement can only exist within a clocked process.
Here is a code example to specify a 3-write and 2-read memory module:
p1: process(CLK) is
begin
if CLK'event and CLK = '1' then
if C1 then
An_Array(a)
Reply to
Weng Tianxiang
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Same comments as with the first 'definition' which is that it provides no b enefit to anyone that uses VHDL and it expands the keyword list of the stan dard without providing any benefit. Good luck with that. Now that VHDL-20 19 is near the end of the finish line, VHDL-2030 won't be far behind, that will be your next opportunity.
Each instance of 'if_2' in your example process can be replaced with today' s 'if' and the example process works with every VHDL standard that has been released to date. So, if 'if_2' ever became part of the standard, then an yone who would use it is locking themselves into requiring use of a particu lar standard when it is not needed. That is poor design practice. I guess users will just have to muddle through by typing the exact same thing exce pt for the needless '_2'.
Kevin Jennings
Reply to
KJ
I download someone's key code from pastebin.com and copy it here for easy d iscussion. He claims that the following code describes a 10-write and 10-re ad memory module, but he admitted that a synthesizer does not run it well.
architecture example of memtest is ... . shared variable memory : memory_t; -- !!! begin . . blks : for i in 0 to PORT_COUNT-1 generate . . . memport : process(clocks(i)) . . . begin . . . . . if rising_edge(clocks(i)) then . . . . . . . if stbs(i) = '1' then . . . . . . . . . memory(addrs(i)) := writes(i); . . . . . . . end if; . . . . . . . reads(i)
Reply to
Weng Tianxiang
discussion. He claims that the following code describes a 10-write and 10- read memory module, but he admitted that a synthesizer does not run it well .
es it, and hope some experts explain it to me further.
when you ran it comes down to the synthesizer not the language." That is ab solutely not as good as you promised what you have describe it before: the method to generate an n-write and m-read memory module is well established in HDL grammar. If a well defined code based on a grammar cannot run well b y a synthesizer, can I believe what you say?
ll?
Yes, it describes a single memory with N ports where N is defined by PORT_C OUNT. What part of the code do you find confusing?
There is no shortcoming in the language. This code describes the memory pr operly. If a synthesizer can't synthesize this code for 10 ports that is a problem with the synthesizer, not the language. I'm willing to bet you wi ll have a hard time finding a library module for a 10 port memory.
If you don't understand the language enough to know this code describes an N port memory, you really are not in a position to tell the rest of us how the language should be changed to accommodate your lack of understanding.
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  Rick C. 

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Reply to
Rick C
sy discussion. He claims that the following code describes a 10-write and 1 0-read memory module, but he admitted that a synthesizer does not run it we ll.
utes it, and hope some experts explain it to me further.
l when you ran it comes down to the synthesizer not the language." That is absolutely not as good as you promised what you have describe it before: th e method to generate an n-write and m-read memory module is well establishe d in HDL grammar. If a well defined code based on a grammar cannot run well by a synthesizer, can I believe what you say?
well?
_COUNT. What part of the code do you find confusing?
properly. If a synthesizer can't synthesize this code for 10 ports that is a problem with the synthesizer, not the language. I'm willing to bet you will have a hard time finding a library module for a 10 port memory.
n N port memory, you really are not in a position to tell the rest of us ho w the language should be changed to accommodate your lack of understanding.
Rick, I think your conclusion is made too earlier.
Here is what the code author responses:
The synthesizer doesn?t do well because any additional port to a me mory makes it exponentially harder to implement.
You can implement a multi-memory in 3 ways:
real physical designed hard memory block. These are the dual-ported memorie s of FPGAs
flip-flops or latch based arrays. These are very area inefficient.
weird architectures that use dual-ported memories to build memories with a larger number of ports. That?s the paper that you linked too. It is extremely area inefficient as well.
In practice. designers avoid multi-ported memories like the plague because they are very costly. It has nothing to do with language features. As shown above: writing the RTL for a 10-ported memory is trivial. You don? t need new keywords for it.
For example: a 10 ported read/write memory would require on the order of 10 0 RAMs using the paper that you linked to.
That is why synthesis tools don?t infer them: you?d give de signers a lot of rope to hang themselves with a feature for which there is no demand.
Rick, After seeing the code author's response do you have any new idea?
Weng
Reply to
Weng Tianxiang
:
easy discussion. He claims that the following code describes a 10-write and 10-read memory module, but he admitted that a synthesizer does not run it well.
ecutes it, and hope some experts explain it to me further.
ell when you ran it comes down to the synthesizer not the language." That i s absolutely not as good as you promised what you have describe it before: the method to generate an n-write and m-read memory module is well establis hed in HDL grammar. If a well defined code based on a grammar cannot run we ll by a synthesizer, can I believe what you say?
o well?
RT_COUNT. What part of the code do you find confusing?
y properly. If a synthesizer can't synthesize this code for 10 ports that is a problem with the synthesizer, not the language. I'm willing to bet yo u will have a hard time finding a library module for a 10 port memory.
an N port memory, you really are not in a position to tell the rest of us how the language should be changed to accommodate your lack of understandin g.
memory makes it exponentially harder to implement.
ies of FPGAs
a larger number of ports. That?s the paper that you linked too. It is extremely area inefficient as well.
e they are very costly. It has nothing to do with language features. As sho wn above: writing the RTL for a 10-ported memory is trivial. You don? ?t need new keywords for it.
100 RAMs using the paper that you linked to.
designers a lot of rope to hang themselves with a feature for which there i s no demand.
I'm not clear on what your points are. I don't see anything in this post t hat contradicts anything I've said. What did I say that you are addressing ?
BTW, it is hard to follow the conversation when you keep starting new threa ds on the same topic.
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  Rick C. 

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Reply to
Rick C
Because there are no suitable primitives for the synthesis tool to map to. This is not the say the synthesis vendor couldn't infer a decuple (had to look this up) port memory block using existing techniques like templates, attributes, synthesis directive etc but I suspect the number of configurations would be too large for very little return.
As many others have told you adding a new keyword to the language will not make this any easier!
I would be interested to find out what circuit needs a true decuple port memory block. Processor register files and network controllers require a large number of read/write ports but I am sure it is not as high as 10.
Regards, Hans
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Reply to
HT-Lab
sy discussion. He claims that the following code describes a 10-write and 1 0-read memory module, but he admitted that a synthesizer does not run it we ll.
utes it, and hope some experts explain it to me further.
l when you ran it comes down to the synthesizer not the language." That is absolutely not as good as you promised what you have describe it before: th e method to generate an n-write and m-read memory module is well establishe d in HDL grammar. If a well defined code based on a grammar cannot run well by a synthesizer, can I believe what you say?
well?
Hi Hans,
I remember that you mentioned that you implemented a 8*8 port memory module using technique based on paper "Efficient Multi-Ported Memories for FPGAs" .
Can you disclose more details and your experiences about your implementatio n? And what is the best technique to design a CPU register file in your opi nion?
In my project, I need multiple 2-write and 2 read port memory, true dual po rt memory does not meet my requirement. I estimate that I need 4 RAM with e ach having 1-write and 1-read port.
Even though my project is still in logic design stage and there is no probl em for me to simulate the logic, based on current logic design: an array ca n be read n times and written m times: when multiple writing to an array in a process I guess a simulator would only write any data at the written add ress once it meets an assignment statement that would guarantee the last wr ite is valid if their writing addresses are same.
The technique based on the paper needs n*
m RAM blocks if each RAM block has one write and one read port. What role may a dual port memory block play?
Thank you.
Weng
Reply to
Weng Tianxiang
easy discussion. He claims that the following code describes a 10-write and 10-read memory module, but he admitted that a synthesizer does not run it well.
ecutes it, and hope some experts explain it to me further.
ell when you ran it comes down to the synthesizer not the language." That i s absolutely not as good as you promised what you have describe it before: the method to generate an n-write and m-read memory module is well establis hed in HDL grammar. If a well defined code based on a grammar cannot run we ll by a synthesizer, can I believe what you say?
o well?
t
a
le using technique based on paper "Efficient Multi-Ported Memories for FPGA s".
ion? And what is the best technique to design a CPU register file in your o pinion?
port memory does not meet my requirement. I estimate that I need 4 RAM with each having 1-write and 1-read port.
blem for me to simulate the logic, based on current logic design: an array can be read n times and written m times: when multiple writing to an array in a process I guess a simulator would only write any data at the written a ddress once it meets an assignment statement that would guarantee the last write is valid if their writing addresses are same.
as one write and one read port. What role may a dual port memory block play ?
You think too much in terms of the HDL you have written. There is no way f or the HDL to know the two addresses are equal, so the first/last thing doe sn't enter into the matter. That is also why the suggested code to infer a multiple write port memory is with a shared variable and separate processe s.
Remember that an HDL is a hardware description language. Exactly what hard ware are you trying to describe? That is, how do you expect the tools to i mplement your multiple write port memory?
The fact that your code simulated means nothing if the code can't be synthe sized to working hardware.
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  Rick C. 

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Reply to
Rick C
Hi Weng,
I actually used the XOR variant (not multipumped) to implement a 4W8R port. You can find the paper here:
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and more papers on the main page:
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That all depends on your design. In my case I could use the XOR variant as I have a pipelined design were I could latch the register file's read request early on in the pipeline and then in a later stage XOR with the new results for the write request. The XOR is the most area efficient but was the most complicated to add to my design (due to data hazards and the fact that each write request also needs a read request).
In that case forget about LaForest Et.al paper and simple use one of the core wizards like Intel's MegaWizard, Xilinx's Coregen etc. You get 2W2R area/speed optimised design with lots of configurable options.
The core wizards gives you the option what should happen if you read/write to the same address.
Not sure what you are asking, you need DPRAM's as the basic building block for a a multi-port design. If you have the time I would suggest to implement the various versions and see how they behave, I learned a lot from it.
Good luck, Hans
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Reply to
HT-Lab
dule using technique based on paper "Efficient Multi-Ported Memories for FP GAs".
ation? And what is the best technique to design a CPU register file in your opinion?
l port memory does not meet my requirement. I estimate that I need 4 RAM wi th each having 1-write and 1-read port.
roblem for me to simulate the logic, based on current logic design: an arra y can be read n times and written m times: when multiple writing to an arra y in a process I guess a simulator would only write any data at the written address once it meets an assignment statement that would guarantee the las t write is valid if their writing addresses are same.
has one write and one read port. What role may a dual port memory block pl ay?
Hans, Thank you very much for your help and sharing your experience with me, and 2 links are valuable. I will spend time reading those specifications and pa pers carefully.
Because VHDL has means to generate a n*m port code, so my if_2 idea is mean ingless and dead. I am sorry for your times spent on those related posts.Of cause I learned a lot.
Also thank Rick and JK for your time.
Weng
Reply to
Weng Tianxiang
No need to apologise, how many of us can say we have 4(?) granted US patents. Please continue to share your ideas and questions.
Regards, Hans.
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Reply to
HT-Lab
On Sunday, September 29,
Hans, Thank you for your experience, help and encouragement.
Your 4*8 memory module and a 4 computer system are a great achievement!!!
Weng
Reply to
Weng Tianxiang

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