Description

When I simulate a POS PHY L4 core using NC-Verilog (by Cadence) or VCS (by Synopsys), unusual and inconsistent behaviors occur. Behaviors include: 

- Packets being dropped. 

- SnkFFErr being asserted. 

- Packets being issued to the user/FIFO interface without SOP (i.e., SnkFFSOP is being dropped). 

- SnkFFData bytes being swapped. 

- An error being reported on every other training pattern. 

This problem may not be limited to NC-Verilog and VCS. It could occur on other simulators as well.

Solution

When a PL4 core is simulated in Verilog, race conditions that show the above behaviors can occur. You may avoid the failures above by not using the following simulator switches (options): 

For NC-Verilog (Cadence), simulate without: 

+delay_mode_distributed  

+noneg_tchks 

For VCS (Synopsys), simulate without: 

+no_specify