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DDR DQ(S) signals hi-Z in simulation

Posts: 70
Registered: ‎03-27-2009

DDR DQ(S) signals hi-Z in simulation

I am using EDK9.2.02 and Spartan3E 1600e dev brd, I quickly created a edk microblaze design with only rs232 and mpmc ddr in order to see the activities on ddr dq and dqs, first I downloaded the design to s3e 1600e brd and from hyperterminal I have seen memory test pass which is expected, then I generated  simulation HDL files and test bench and hooked-up the memory model from micron in my system_tb.vhd and add compile command in system.do, then invoke modelsim se 6.2b run for 1 ms, from the wave window, I saw signal MPMC_initDone went '1' a bit after 200 us which is good, however, the DDR_DQ and DDR_DQS were constant 'Z', I don't know if there is anything I am missing, pls advise.

here is the steps I did for simulation:

1)Project -> Project Options -> HDL and Simulation tab, tick 'Generate test bench template'.

2)Simulation -> Generate simulation HDL Files.

3)In system_tb.vhd, declare ddr.v (from Micron) using vhdl syntax and hook it up with signlas from edk system.

4)copy micron ddr model ddr.v and related files to project\simulation\behavioral.

5) in system.do, add "vlog -incr -work work +define+x16 +define+FULL_MEM +define+sg6T "ddr.v" " before testbench compile command.

6)invoke modelsim, execute do system_setup.do, then type C,S,W, there is no error or warnings when testbench was compiled.

7) check wave window.



Posts: 70
Registered: ‎03-27-2009

Re: DDR DQ(S) signals hi-Z in simulation

stii nobody gave a shout???
Posts: 6
Registered: ‎11-01-2008

Re: DDR DQ(S) signals hi-Z in simulation

[ Edited ]



They are supposed to be Hi-Z when idle. DQ and DQS are inout signals to allow the DDR_controller to drive them when writing and the DDR_chip when reading.


If you issue a READ_CMD, DQS will start toggling if initialization was successful and everything went ok.

DQS is a strobe transmitted by the DDR SDRAM during READs and by the memory controller during WRITEs. DQS is edge-aligned with data for READs and center-aligned with data for WRITEs.



Tools: ISE 10.1 SP3, ISim 10.1.


I'm developing a DDR controller for the SP31600-StarterKit and I'm using the Micron DDR model 46v32m16 (the one provided with MIG) and writing operations happen to succeed but for every read operation DQ[15:0] appears as XXXX, autorefresh and precharge are already taken care of.

Does anybody knows if it's an issue with the model or with ISim?



Message Edited by santiagordgz on 05-11-2009 02:36 PM
Posts: 3
Registered: ‎02-09-2011

Re: DDR DQ(S) signals hi-Z in simulation

Similar problem, but a little different.


In ISE 13.4, simulating with ISIM, DDR2 controller wrapped in MPMC.  Device = Spartan 6.


DQS and DQS_N signals are X from the beginning of time and never change.  Tracing down the hierarchy I see that they are driven by 2 primitives inside the controller: an iobuf and pulldown.  The pulldown is the one driving 'X'.  The iobuf has legal, non-Z inputs on its I and T ports and during (attempted) initialization when T toggles, the X on the net does not change.


This is a VHDL design.


I have done this before on another project with a Verilog top-level design and it worked fine!  I even went back and re-ran my old simulation to see for certain and there was no similar problem.


Things I've tried:

 - Run with and without DDR memory model in testbench

 - Run with and without additional "PULLDOWN" in the testbench

 - Run fuse specifying --timescape 1ps/1ps --override_timeunit and --override_timeprecision


None of these have any effect.