Forum Discussion

LukiLeu's avatar
LukiLeu
Icon for New Contributor rankNew Contributor
2 months ago

Quartus crashes on long carry chain in Agilex 5 FPGAs

We try to manually place a carry chain in the Agilex 5 FPGAs which consists of more than 40 LABs. When we place this carry chain using set_location_assignment, Quartus crashes during the placement phase whenever the carry chain is longer than 40 LABs.

Is it expected that the carry chain cannot be made longer than 40 LABs in the Agilex 5 FPGAs?

Crash was observed on Quartus 25.3 and Quartus 26.1 for the devices A5ED065BB32AE4S and A5ED013BB32AE4SCS.

Internal Error: Sub-system: FLABS, File: /quartus/fitter/flabs/flabs_util.cpp, Line: 96 p_to_fill->next == FLABS_OPEN

Compilation

4 Replies

  • ZiYingE_Altera's avatar
    ZiYingE_Altera
    Icon for Contributor rankContributor
    1 hour ago

    Hi LukiLeu​, 

    I am Zi Ying and am currently assisting Kenny with this support ticket while he is out of the office.

    I also heard from Kenny about your bike accident. Wishing you a smooth and speedy recovery.

    Based on feedback from our internal engineering team, Agilex 5 supports approximately 46 to 47 LABs within a single continuous sector. As such, a single uninterrupted 50-LAB carry chain is not expected to fit on this device.

    To help us determine the best next step, could you please confirm the minimum continuous carry-chain length required for your TDC to meet its reliability and accuracy targets? For example, would 43 LABs as your original design be sufficient, or is a chain close to 50 LABs essential?

    This information will help us determine the most appropriate workaround for your design.

    Thank you!

    Regards, 
    ZiYingE_Altera

  • FvM's avatar
    FvM
    Icon for Super Contributor rankSuper Contributor
    2 months ago

    Hi,
    as far as I'm aware of, Quartus has no problems to synthesize long carry chains for Agilex 5. You can try with adder or e.g. priority encoder. I guess the problem is about manually assigning placement. What do you want to achieve? Does your design compile with automatic placement? Are you sure that the specified placement can be routed? 

    Regards
    Frank

  • LukiLeu's avatar
    LukiLeu
    Icon for New Contributor rankNew Contributor
    2 months ago

    Hi Kenny, 

    Unfortunately, I can't make the design publicly available.

     We built the chain by cascading multiple tennm_lcell_comb components.