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AR# 12012

4.1i UNISIM, SIMPRIM - Simulation Limitations of Dual-Port Block RAM models (VHDL, Verilog)

Description

Keywords: UniSim, SimPrim, Simulation, functional, timing, VHDL, Verilog, block RAM, blockRAM, ramb4

Urgency: Standard

General Description:
A number of limitations exist in the Dual-Port BlockRAM simulation models (as compared to the hardware features).

Solution

1

Functional Simulation

1. The instance name is not reported for memory collision in RAMB16* Components. (This problem occurs in Verilog simulation only.) If a memory collision is detected, the error message does not report the instance name. Please take special care to avoid memory collisions during simulation and device operation. This problem will be fixed in a future release of the software tools.

2. RAMB16* models do not detect all combinations of collisions. (This problem occurs in both VHDL and Verilog simulation.) Dual-port Block RAM components may not detect all combinations for collisions. Please take special care to avoid memory collisions during simulation and device operation. This problem will be fixed in a future release of the software tools.

2

Timing Simulation

1. RAMB16* models do not allow variations in collision severity. (This problem occurs in VHDL timing simulations only.) Dual-port Block RAM components do not allow the user to vary the severity of the memory collisions. Because of this, the simulation stops when it runs into a memory collision. Please take special care to avoid memory collisions during simulation and device operation. This problem will be fixed in a future release of the software tools.

2. Incorrect collision detection for some stimulus combinations in RAMB4* Components. (This problem occurs in Verilog simulation only.) Using the Verilog SIMPRIM RAMB4 Dual-Port RAM components, if the same clock is being used for Clock Port A and Port B, proper collision detection is not correctly identified. Please ensure that you do not read from the same port that is being written to on the same clock cycle. This problem will be fixed in a future release of the software tools.
AR# 12012
Date Created 07/23/2001
Last Updated 05/05/2004
Status Archive
Type General Article