There is no consistent definition of a speedgrade for all devices. Even for Xilinx,
speed grades mean different things depending on if you are referring to a FPGA or a CPLD. For CPLDs, speed grades represent the time it takes for logic to go through the device (eg. in <= out). So a -10 device means that the device is guaranteed to send a signal from an input pin thru to an output pin in under 10 nS. So for CPLDs, the lower the number, the faster the part is. This is standard for CPLDs across all vendors so this can be used for device comparison purposes.
what is the valve of standard grade(FPGA)
However for FPGAs, they don't use the same definition for speedgrade. Originally speed grades for FPGAs represented the time through a look up table but now the speedgrade doesn't actually repesent a timing path. I am not sure if it is the same for other vendors, but for Xilinx FPGAs higher numbers are faster. Each speedgrade increment is ~15% faster than the one before it. So a -5 is 10% faster than a -4 speedgrade.
Determining the speed grade of Xilinx devices
Q:
I am having some trouble understanding the numbering system Xilinx uses for speed grade. Could someone explain what the numbers are and how to tell which speed grade is installed on my XS40. FWIW I have an XC4010XL FPGA. The available speed grade choices are -1, -2 -3, or -09.
A:
You usually see the speed grade imprinted on the chip on a line by itself. For an XC4000, you might see "3C" printed on the chip. That means the chip has speed grade -3. (I think the "C" stands for commercial temperature range.)
For XC4000 devices, the number is roughly equivalent to the propagation delay through a CLB. So a -3 speed grade implies 3 ns of delay through a level of logic, -2 means 2 ns. Don't be mislead by -09, it actually means 0.9 ns of delay.
The situation changes with Spartan and Virtex devices. Now a larger number means the device is faster.
Reference : http://www.xess.com/faq/M0000236.HTM
Question:
From: vlsigeek Date Posted : 12/11/2004 4:42:49 AM Hi guys,
What is the speed grade in FPGA. What it tells actually.
Thanks in advance,
Soundar
Comments:
From: vlsi_giant Posted : 12/27/2004 12:54:29 AMHi It is actually the min I/O delay for that device. Ex: for altera MAX device EPM7128... -15 this -15 indicates this device has min of 15 ns. i/o delay.
yogesh
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speedgrade
Category: FPGA
Question:
From: surekha29 Date Posted : 7/19/2006 5:19:41 AM While using xilinx synthesis tool, in the synthesis reports I found a term called speedgrade : -6, what does this actually mean??
Comments:
From: muthu_kumar Posted : 7/20/2006 12:53:49 AM Hi, Use this field to test a speedgrade with your design. Changing the speedgrade helps determine a need to target a faster device to meet your timing requirements, or if using a slower speedgrade still meets timing constraints. Select a speedgrade from the pull-down list, which contains the available speed grades for the target device.
Changing the speedgrade in the Options tab tests it with the design; it does not change the speedgrade in your FPGA design file. regards muthukumar.p
From: vikas Posted : 7/27/2006 6:06:01 AM THE FREQUENCY OF DESIGN DEPENDS UPON SELECTED DEVICESPEED GRADE. suppose u have design that is working on 50 mhz,with a device whose speedgrade is 6. now if u want to work at 70 Mhz frequency.and with speedgrade 6 u r not acheving that much frequency with that device.then if u take same device with more speedgrade then this its sure that ur design fequncy will also increase but it is more costly then then the earlier.
From: vikas Posted : 7/27/2006 6:07:11 AM i think that is the importance of speedgrade.
From: vikas Posted : 7/27/2006 6:07:13 AM i think that is the importance of speedgrade.
From: surekha29 Posted : 7/28/2006 2:20:34 AM Thanks for ur comments Muthu Kumar and Vikas. In my search I have found my answer, n thought of sharing...
Internal frequency is the speed at which CPLDs/FPGAs can perform operations or transfer data internally. The propagation delay is the time interval between the application of an input signal and the occurrence of the corresponding output in a logic circuit. Speedgrade indicates the delay in nanoseconds (ns) through a macrocell in the device. For example, a device with a speedgrade of –10 has a delay of 10 ns through a macrocell. Devices with low speedgrade numbers run faster than devices with high-speedgrade numbers.
speedgrade of -09 implies a delay of 0.9ns.
From: muthu_kumar Posted : 7/30/2006 11:23:51 PM Hi surekha,Where u get these ideas?provide the source. i have doubt about your answers.myself and vikas going into the same direction i.e when the device speedgrade is increase then the speed of the device also increase.but your answer is different.I warm welcome to all the readers.pls share your points about this question. regards muthukumar.p
From: surekha29 Posted : 7/31/2006 2:12:06 AM Hello, I have seen the details at the following links.
I hope the definition of speedgrade for FPGA and CPLD are the same. I think the minus indicates the samething, i.e., as the delay increases the speed(frequency) reduces.
From: muthu_kumar Posted : 7/31/2006 11:44:50 PM Hi thanks ,to day i got the new idea from u. xilinx fpga point of view -7 speedgrade device faster than -6 speedgrade device. But altera cpld point of view -10 speedgrade device slower than -9 speedgrade device. ok -10 and -9 are denotes the macrocell propagation delay. but if u know any specification of -7 or -6 in FPGA.Anybody knows pls let me know. regards muthukumar.p
From: gargji Posted : 8/2/2006 4:58:03 AM Hi Muthu, I can give you some more clearification about FPGA speed grades. In an FPGA the fabricator devides the devices in to some categories. Speedgrade -7 means that there is a range of macrocell delay in FPGA which is kept in this category. But in cplds -10 means the macrocell delay is 10 ns. Hope the same is helpfull. rgds
From: manish. Posted : 9/2/2006 5:15:56 PM surekha n all comment after checking this site
http://www.xess.com/faq/M0000236.HTM
From: gauravkshri Posted : 11/9/2006 1:14:49 AM hi guys, I just read ur comments. If I have been told to describle Speedgrade in a sentence,I would say " Its a minimum i/o delay". This means a signal will take atleast this much of time to travel from i/p to o/p.
From: gauravkshri Posted : 11/9/2006 1:21:26 AM hi, You usually see the speedgrade imprinted on the chip on a line by itself. For an XC4000, you might see "3C" printed on the chip. That means the chip has speedgrade -3. (I think the "C" stands for commercial temperature range.)
For XC4000 devices, the number is roughly equivalent to the propagation delay through a CLB. So a -3 speedgrade implies 3 ns of delay through a level of logic, -2 means 2 ns. Don't be mislead by -09, it actually means 0.9 ns of delay.
The situation changes with Spartan and Virtex devices. Now a larger number means the device is faster.
