Forum Discussion
Occasional ContributorTiming closure on Arria 10
I am trying to close timing on an Arria 10 Design (A057K2F40I2). I would like to know if some of the problems I am seeing are device limitations, or just tool issues or operator error.
The first concerns setup time to I/O registers. Here is an example, from Chip Planner:
The delay from the pad to the register input exceeds 5 ns (see below).
This seems a bit high to me, but perhaps mediocre I/O cell performance is a limitation of mid-priced FPGAs.
The second problem regards synthesis results, and the effect therof on timing. We have a block of 32-bit registers, which can be accessed via a PCIe endpoint and Avalon shim interface. There are about 100 - 150 registers, and a 14-bit address. The readback mux for the register block is failing setup time by a significant margin. I would expect the mux for each read data bit to be implemented separately, and the resulting combinatorial circuit would have fewer than 200 inputs. With 6-input LUTs, it should be possible to implement that logic in three or four levels. But I am seeing on the order of 30 levels:
I have added a couple of extra clock ticks and am using a multicycle constraint, but I am still seeing a bunch of paths that don't make it.
Here is the chip planner view for the above mux:
So is this an Arria 10 limitation? I have tried Prime Pro 18.1 and 19.2, as well as Prime Standard 18.2, and I get similar results in each case.
15 Replies
KhaiChein_Y_IntelRegular Contributor
Hi,
The screenshot cannot be seen. Could you reattach? Do you have the block diagram?
Thanks.
SeadogI am sorry, but I am unable to insert or attach image files (not sure if this is some IT problem on my end or what). Regardless, I think there is enough information in my posting to describe the problem, primarily:
- Internal delay in an I/O cell (pad to register input) can be as high as 5 ns
- a combinatorial circuit with ~150 inputs requires 30 levels of 6-input LUTs (not just 30 LUTs, a a timing chain 30 LUTs deep).
Thanks again.
sstrellSuper Contributor
Can you post your .sdc file? That will be much more useful to see than Chip Planner screenshots.
#iwork4intel
- Seadog
No, I can't, sorry.
- sstrell
Can you at least post Timing Analyzer reports on the failing paths, especially the Data Path tab in a detailed report, to see all the resources the failing paths are passing through?
#iwork4intel
- Seadog
Here is the list of LABs and MLABs for one path. I would post the entire report, but it would not format nicely. To my mind, this is way too many layers for 6-input LUTs.
FF_X54_Y124_N38
FF_X54_Y124_N38
MLABCELL_X55_Y126_N39
MLABCELL_X55_Y126_N39
MLABCELL_X55_Y126_N39
LABCELL_X54_Y127_N30
LABCELL_X54_Y127_N30
LABCELL_X54_Y127_N30
LABCELL_X45_Y130_N54
LABCELL_X45_Y130_N54
LABCELL_X45_Y130_N54
MLABCELL_X49_Y129_N57
MLABCELL_X49_Y129_N57
MLABCELL_X49_Y129_N57
LABCELL_X50_Y127_N27
LABCELL_X50_Y127_N27
LABCELL_X50_Y127_N27
LABCELL_X51_Y127_N0
LABCELL_X51_Y127_N0
LABCELL_X51_Y127_N0
LABCELL_X51_Y125_N6
LABCELL_X51_Y125_N6
LABCELL_X51_Y125_N6
LABCELL_X50_Y125_N9
LABCELL_X50_Y125_N9
LABCELL_X50_Y125_N9
LABCELL_X51_Y122_N24
LABCELL_X51_Y122_N24
LABCELL_X51_Y122_N24
LABCELL_X50_Y122_N0
LABCELL_X50_Y122_N0
LABCELL_X50_Y122_N0
LABCELL_X51_Y120_N54
LABCELL_X51_Y120_N54
LABCELL_X51_Y120_N54
LABCELL_X51_Y120_N42
LABCELL_X51_Y120_N42
LABCELL_X51_Y120_N42
LABCELL_X50_Y119_N42
LABCELL_X50_Y119_N42
LABCELL_X50_Y119_N42
MLABCELL_X49_Y116_N9
MLABCELL_X49_Y116_N9
MLABCELL_X49_Y116_N9
LABCELL_X48_Y116_N18
LABCELL_X48_Y116_N18
LABCELL_X48_Y116_N18
MLABCELL_X42_Y117_N0
MLABCELL_X42_Y117_N0
MLABCELL_X42_Y117_N0
MLABCELL_X38_Y121_N12
MLABCELL_X38_Y121_N12
MLABCELL_X38_Y121_N12
LABCELL_X37_Y122_N24
LABCELL_X37_Y122_N24
LABCELL_X37_Y122_N24
LABCELL_X35_Y124_N51
LABCELL_X35_Y124_N51
LABCELL_X35_Y124_N51
LABCELL_X34_Y124_N54
LABCELL_X34_Y124_N54
LABCELL_X34_Y124_N54
LABCELL_X30_Y120_N51
LABCELL_X30_Y120_N51
LABCELL_X30_Y120_N51
LABCELL_X31_Y120_N9
LABCELL_X31_Y120_N9
LABCELL_X31_Y120_N9
LABCELL_X30_Y116_N48
LABCELL_X30_Y116_N48
LABCELL_X30_Y116_N48
LABCELL_X31_Y116_N18
LABCELL_X31_Y116_N18
LABCELL_X31_Y116_N18
LABCELL_X34_Y116_N54
LABCELL_X34_Y116_N54
LABCELL_X34_Y116_N54
LABCELL_X33_Y119_N0
LABCELL_X33_Y119_N0
LABCELL_X33_Y119_N0
MLABCELL_X29_Y113_N24
MLABCELL_X29_Y113_N24
MLABCELL_X29_Y113_N24
LABCELL_X35_Y120_N42
LABCELL_X35_Y120_N42
FF_X35_Y120_N44
FF_X35_Y120_N44
- sstrell
These are just the locations of the resources the path is going through. I would want to see the node names that correspond to your design. Screenshots from the Timing Analyzer would be easiest or you can save the report as ASCII text.
#iwork4intel
- Seadog
Well, the node names are mostly machine-generated gibberish, but here they are:
ctl_regs_inst|read_addr[14]|q
ctl_regs_inst|read_addr[14]~la_lab/laboutb[5]
ctl_regs_inst|reduce_nor_339~2|datac
ctl_regs_inst|reduce_nor_339~2|combout
ctl_regs_inst|reduce_nor_339~2~la_mlab/laboutb[7]
ctl_regs_inst|reduce_nor_173|datab
ctl_regs_inst|reduce_nor_173|combout
ctl_regs_inst|reduce_nor_173~la_lab/laboutb[1]
ctl_regs_inst|i6015~0|datad
ctl_regs_inst|i6015~0|combout
ctl_regs_inst|i6015~0~la_lab/laboutb[16]
ctl_regs_inst|i6040|datad
ctl_regs_inst|i6040|combout
ctl_regs_inst|i6040~la_mlab/laboutb[18]
ctl_regs_inst|i6061~0|datac
ctl_regs_inst|i6061~0|combout
ctl_regs_inst|i6061~0~la_lab/laboutt[18]
ctl_regs_inst|i6078~1|dataf
ctl_regs_inst|i6078~1|combout
ctl_regs_inst|i6078~1~la_lab/laboutt[1]
ctl_regs_inst|i6103~0|dataf
ctl_regs_inst|i6103~0|combout
ctl_regs_inst|i6103~0~la_lab/laboutt[4]
ctl_regs_inst|i6111~0|dataf
ctl_regs_inst|i6111~0|combout
ctl_regs_inst|i6111~0~la_lab/laboutt[6]
ctl_regs_inst|i6132~0|datae
ctl_regs_inst|i6132~0|combout
ctl_regs_inst|i6132~0~la_lab/laboutt[17]
ctl_regs_inst|i6166~2|dataf
ctl_regs_inst|i6166~2|combout
ctl_regs_inst|i6166~2~la_lab/laboutt[0]
ctl_regs_inst|Select_34~1|dataf
ctl_regs_inst|Select_34~1|combout
ctl_regs_inst|Select_34~1~la_lab/laboutb[17]
ctl_regs_inst|i6208~0|dataf
ctl_regs_inst|i6208~0|combout
ctl_regs_inst|i6208~0~la_lab/laboutb[9]
ctl_regs_inst|i6229~1|datae
ctl_regs_inst|i6229~1|combout
ctl_regs_inst|i6229~1~la_lab/laboutb[9]
ctl_regs_inst|i6250~2|dataf
ctl_regs_inst|i6250~2|combout
ctl_regs_inst|i6250~2~la_mlab/laboutt[7]
ctl_regs_inst|i6271~2|dataf
ctl_regs_inst|i6271~2|combout
ctl_regs_inst|i6271~2~la_lab/laboutt[13]
ctl_regs_inst|i6288~1|dataf
ctl_regs_inst|i6288~1|combout
ctl_regs_inst|i6288~1~la_mlab/laboutt[0]
ctl_regs_inst|i6309~0|dataf
ctl_regs_inst|i6309~0|combout
ctl_regs_inst|i6309~0~la_mlab/laboutt[9]
ctl_regs_inst|i6343~0|datae
ctl_regs_inst|i6343~0|combout
ctl_regs_inst|i6343~0~la_lab/laboutt[16]
ctl_regs_inst|i6343|datae
ctl_regs_inst|i6343|combout
ctl_regs_inst|i6343~la_lab/laboutb[15]
ctl_regs_inst|i6364~0|datae
ctl_regs_inst|i6364~0|combout
ctl_regs_inst|i6364~0~la_lab/laboutb[16]
ctl_regs_inst|i6385|dataf
ctl_regs_inst|i6385|combout
ctl_regs_inst|i6385~la_lab/laboutb[14]
ctl_regs_inst|i6406~0|datae
ctl_regs_inst|i6406~0|combout
ctl_regs_inst|i6406~0~la_lab/laboutt[7]
ctl_regs_inst|i6427|dataf
ctl_regs_inst|i6427|combout
ctl_regs_inst|i6427~la_lab/laboutb[12]
ctl_regs_inst|i6448~0|dataf
ctl_regs_inst|i6448~0|combout
ctl_regs_inst|i6448~0~la_lab/laboutt[13]
ctl_regs_inst|i6460|dataf
ctl_regs_inst|i6460|combout
ctl_regs_inst|i6460~la_lab/laboutb[17]
ctl_regs_inst|i6510|dataf
ctl_regs_inst|i6510|combout
ctl_regs_inst|i6510~la_lab/laboutt[1]
ctl_regs_inst|Select_26~118|dataa
ctl_regs_inst|Select_26~118|combout
ctl_regs_inst|Select_26~118~la_mlab/laboutt[16]
ctl_regs_inst|Select_26~119|datad
ctl_regs_inst|Select_26~119|combout
ctl_regs_inst|reg_rdbk_data[8]|d
ctl_regs_inst|reg_rdbk_data[8]
The combinatorial path, in this case is from read_addr[14] to reg_rdbk_data[8], and the RTL code is a case statement.
- sstrell
I would also need to see the timing numbers. Is there no way you can just post the whole report? And is there a reason why the .sdc can't be posted? That would help a lot.
#iwork4intel
- Seadog
You will have to explain to me how the timing values, or the .sdc file, will lead to an answer as to why the synthesizer/P&R/fitter tools are implementing this particular bit of code in a way in which it can not possibly make timing, because that is what I need to understand.
