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FIFO depth requirement

fragnen

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Data is being written in a FIFO as 85 data in 100 clock cycles and the data comes in the first 85 clock cycles and in the remaining last 15 clock cycles out 0f the 100 clock cycles no data is coming. So for every 100 clock cycles for the first 85 clock cycles data is being written in a FIFO. Will this fact that data is not coming every last 15 clock cycles out of every 100 clock cycles help to decide about the FIFO depth and how?
 

barry

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You get today's award for most confusing question.

Are you writing 85 data in 85 cycles or 100 cycles? First you say you're writing 85 data in 100 cycles, which means that data is written in 85 of the 100 cycles. Then you say "data comes in the first 85 clock cycles". So, which is it? If you write data in 85 cycles, it doesn't matter how many cycles come after that when you're NOT writing data, I don't care if it's 15 cycles or 1500 cycles.

The FIFO depth depends on how fast (and WHEN) you read the data out. You don't mention the read function at all.
 

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barry,

Regardless if the fill is done in a burst or constant rate the problem ends up being a similar set of calculations.

In the OP's case the fill is done in a burst of 85 clock cycles over a period of 100 clock cycles. They are currently missing the drain rate, which I'm assuming is done at 85% of the clock rate of the fill rate.
If it's less than 85% then the FIFO has to be sized to infinity locations.
If it's faster then it can be 1-2 locations.
If the draining of the FIFO is delayed from the start then it's as many locations as needed to account for the delay before reading.

Without the read side of the timing nothing can be determined.
 

fragnen

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You get today's award for most confusing question.

Are you writing 85 data in 85 cycles or 100 cycles? First you say you're writing 85 data in 100 cycles, which means that data is written in 85 of the 100 cycles. Then you say "data comes in the first 85 clock cycles". So, which is it? If you write data in 85 cycles, it doesn't matter how many cycles come after that when you're NOT writing data, I don't care if it's 15 cycles or 1500 cycles.

The FIFO depth depends on how fast (and WHEN) you read the data out. You don't mention the read function at all.
Data is coming in first 85 clock cycles of every 100 clock cycles. So FIFO is being written by the first 85 clock cycles of every 100 write clock cycles.
--- Updated ---

Yes it does,

Go read about the Algebra word problem: "fill drain rate problem"
https://duckduckgo.com/?t=ffnt&q=fill+drain+rate+problem&ia=web
I am aware of usual FIFO depth calculation and the above link stats that only.

Here the query is how the 15 clock cycle of every 100 clock cycle when write data is not coming helps to decide about FIFO depth. For example if write data comes for the first 85 clock cycles for every 95 write clock cycles then how do the 10 clock cycles in which no write data is coming contributes to calculation of FIFO depth.
 
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barry

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Data is coming in first 85 clock cycles of every 100 clock cycles. So FIFO is being written by the first 85 clock cycles of every 100 write clock cycles.
--- Updated ---


I am aware of usual FIFO depth calculation and the above link stats that only.

Here the query is how the 15 clock cycle of every 100 clock cycle when write data is not coming helps to decide about FIFO depth. For example if write data comes for the first 85 clock cycles for every 95 write clock cycles then how do the 10 clock cycles in which no write data is coming contributes to calculation of FIFO depth.
Again, that 85 out of 100 is irrelevant. What matters is the relationship between writing data and READING DATA. You still have said nothing about reading. You can write 85 data in 100 clocks or a million clocks, it doesn't matter without knowing about the reading.
 

dpaul

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Guys let's not forget our forum posts history.....
Fragnen has many other posts on FIFO, where various members have provided detailed answers but none of them had a proper conclusion from the OP. Most of them were unclearly formulated or had missing parameters or were outright confusing.
Here is just one of them - https://www.edaboard.com/threads/designing-asynchronous-fifo-with-odd-number-depth.395513/
So I am not surprised that this Q is coming from the same OP.
 

fragnen

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Guys let's not forget our forum posts history.....
Fragnen has many other posts on FIFO, where various members have provided detailed answers but none of them had a proper conclusion from the OP. Most of them were unclearly formulated or had missing parameters or were outright confusing.
Here is just one of them - https://www.edaboard.com/threads/designing-asynchronous-fifo-with-odd-number-depth.395513/
So I am not surprised that this Q is coming from the same OP.
This post does not have any linkage with other post that was posted related to FIFO from fragnen.

Received answers of the queries sufficiently posted in OP for https://www.edaboard.com/threads/designing-asynchronous-fifo-with-odd-number-depth.395513/ .
 

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Reread the critique of your question in posts 3, 4, and 6.

It was mentioned in all three posts that you can't determine anything about depth until YOU tell us what the read (drain) rate is.
 

barry

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Reread the critique of your question in posts 3, 4, and 6.

It was mentioned in all three posts that you can't determine anything about depth until YOU tell us what the read (drain) rate is.
I give up.
 

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fragnen, explanations have been given, but you insist on asking the same ambiguous question over and over again without adding any information.

It has been explained in multiple posts to solve a FIFO depth problem BOTH the FILL and the DRAIN rate need to be defined. That means the amount of data written over a number of cycles along with the write clock frequency AND the amount of data read over a number of cycles along with the read clock frequency. Without that information NOTHING about the FIFO depth can be defined.

After 11 posts you've only given the part in blue and nothing about any of the items in red. This is after you have been asked to provide information on the read rate..

I second barry and I also give up, as I think your intention is to waste our time.
 
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