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Observer urodacus
Observer
1,214 Views
Registered: ‎04-28-2017

Configuration rate - Artix 7

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Hello,

 

I noticed that my Artix-7 takes a lot of time to boot (approximatively 5 sec) which is usual since i have 17,536,096 bits to load for a xc7a35t and I use a SPI x1 and also, the configuration clock is at 3Mhz (+/- 50%) by default. (theory : 5,8 sec to boot)

 

After doing some calculs with formulas given by Xilinx's datasheet, I knew i could go up to 90 Mhz (so 60MHz because of the +/- 50% tolerance on internal oscillator).

 

I'm kinda new with constrainst files in Vivado (not used to it, only "pure" VHDL and basics constraints) and when I try to change the configrate, I see no change at all.

 

What I did is in my .xdc file (before assigning pins/standards) i wrote :

  • set_property BITSTREAM.CONFIG.CONFIGRATE 22 [current_design]

I wrote 22 because I didn't want to try at maximum value at first.

Am I missing something ?

Thanks in advance for the help you can provide me.

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Voyager
Voyager
1,210 Views
Registered: ‎08-16-2018

Re: Configuration rate - Artix 7

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If you open the implemented design (Flow Navigator, left panel), then click Settings, in the Bitstream settings tab you will see a blue link (Configure additional bitstream settings). Click it, then in Configuration, yo will see a list of drop down lists, one of them titled 'Configuration Rate (MHz)'. These are the valid values. 

You can just try with the fastest speed, if it doesn't work, go one notch slower and so on. If a firmware to release into production, you have to make sure that setting will work in all conditions.

Also, using compressed bitstreams shorten the configuration time.

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7 Replies
Voyager
Voyager
1,211 Views
Registered: ‎08-16-2018

Re: Configuration rate - Artix 7

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If you open the implemented design (Flow Navigator, left panel), then click Settings, in the Bitstream settings tab you will see a blue link (Configure additional bitstream settings). Click it, then in Configuration, yo will see a list of drop down lists, one of them titled 'Configuration Rate (MHz)'. These are the valid values. 

You can just try with the fastest speed, if it doesn't work, go one notch slower and so on. If a firmware to release into production, you have to make sure that setting will work in all conditions.

Also, using compressed bitstreams shorten the configuration time.

View solution in original post

Observer urodacus
Observer
1,184 Views
Registered: ‎04-28-2017

Re: Configuration rate - Artix 7

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It fixed it. I guessed the constraint had to be at the end of the constraint file (or just after another constraint but I don't know which one).

Even suceeded with 50 Mhz which is the max in theory (not 60 Mhz like I posted since it's either 50 or 66).

 

@johnvivmFor my information, how do I know "it will work in all conditions" ?

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Voyager
Voyager
1,180 Views
Registered: ‎08-16-2018

Re: Configuration rate - Artix 7

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Constraints, as far as I know, overwrite each other, so the latest you write "wins"

 

A design that works in your boards in your desk at 20 C doesn't necessarily have to work in all boards because board-to-board variations (for example track impedance or pull-up resistor tolerance) as well as temperature, things are at least expected to work 0 to 85 C. If you are in a company, you will probably have your testing guys and department that will do that for you. If they come back with a sad face, then you will have to lower your speed and redo the test.

 

For a more scientific approach, I have seen some equations (probably in the configuration user guide) to reckon the max config frequency, but still doesn't account for board effects, so the ultimate test is the real world.

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Observer urodacus
Observer
1,171 Views
Registered: ‎04-28-2017

Re: Configuration rate - Artix 7

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@johnvivmwhen i talked about theory it's because I used the formula in the "XAPP586 (Equation 1)". I takes account of FPGA/EEPROM internal latency (sortof) and tracks length. The maximal was about 89MHz so I took 50 MHz (going up to 75MHz because of the 50% tolerance) to be OK.

 

The fact is, I'm currently in a company where I can't just do some tests several times and just changing this element. Either I keep the 50MHz and pray that it'll be OK or either I lower it a bit to be more safe.

 

Sorry for bad english if mistakes were made

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Voyager
Voyager
1,167 Views
Registered: ‎08-16-2018

Re: Configuration rate - Artix 7

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It depends on what type of product and conditions. Is it going to crash a plane with 300 people if it fails to load? Is it in a spacecraft a million miles away or there will always be someone around to press a button and try again? Will it be outdoors with extreme temperatures or in an office? If you reckoned 89 MHz and set 50, it looks like an ample margin.

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Observer urodacus
Observer
1,164 Views
Registered: ‎04-28-2017

Re: Configuration rate - Artix 7

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If it's a project that could crash a plane, believe me I could do such test several times, haha !

 

Anyway, thanks for the help.

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Voyager
Voyager
1,153 Views
Registered: ‎08-16-2018

Re: Configuration rate - Artix 7

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Your boss will tell you because regulations require that for your company to sell it and you getting paid

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