LPM_counter have random values when power on

[yuxi1111]

I would like to ask everyone a question: When using LPM_counter module, only the CLK count port  was used, and no reset port was used. The product started running normally, but random values would appear when powered on a few years later. There are only a few products with problems, and a total of several hundred products. After using the reset port, the problem was resolved. May I ask what is the reason for the problem? thanks

[FvM]

Hi,
all core registers are reset by power-on reset. Is the respective counter clocked by an external clock already running during power-on or by a PLL generated clock? In the former case, it's likely to get inconsistent random counter values because POR isn't released synchronously. In the latter case, counter will hopefully start from zero after PLL clock start. If the counter isn't directly driven from a clk but internal logic, things are more complicated.

Generally, use synchronously released reset for all registers to avoid similar problems.

Regards
Frank

[yuxi1111]

Thanks for your reply! my clock is an external clock. I would like to ask whether the probability of the occurrence of random value will increase with the increase of the use time of the product? Because there was no problem in the beginning, it took a few years before there was a problem. The probability of problems after replacing the chip in the later experiment is greatly reduced.

[yuxi1111]

And there are also many products that have not have problems .

[ShengN_Intel]

Hi,

Do you have any further update or concern?

Thanks,

Best Regards,

Sheng

[FvM]

Hi,
just a guess, power supply start timing may have changed, e.g. due to aging of capacitors. 

[yuxi1111]

OK. Thanks!

[yuxi1111]

YES！My clock is an external clock. I would like to ask whether the probability of the occurrence of random value will increase with the increase of the use time of the product? Because there was no problem in the beginning, it took about six years before there was a problem. And there are also many products that have not have problems .

[sstrell]

Reset should always be used to get the logic in a known state.

[ShengN_Intel]

Hi,

There're so many factors can cause the problem over time such as power-on behavior or voltage levels variations over time, changes in temperature or aging of components, Noise and Interference. Probably better to have reset to initialize the counter to a known state.

Thanks,

Best Regards,

Sheng