Answers Database
M1.2 MAP: Input flip-flops in a bidirectional I/O get removed due to optimization of an output flip-flop whose input is tied to GND.
Record #2457
Product Family: Software
Product Line: FPGA Implementation
Product Part: map
Product Version: 1.2.
Problem Title:
M1.2 MAP: Input flip-flops in a bidirectional I/O get removed due to optimization of an
output flip-flop whose input is tied to GND.
Problem Description:
Urgency: standard
General Description:
Given a circuit consisting of a bidirectional I/O:
IOPAD connected to both the D input of an IFD and
the Q output of an OFDTX_F. The D input of the OFDTX_F is
connected to a constant value of "0" (GND) in the user's
design.
Map simplifies the OFDTX_F to a constant value of 0, and the
IOPAD is correctly configured to drive a constant value of
ZERO in the output direction. However, the zero is
subsequently also pushed around to the D input of the IFD,
and this causes the IFD to be removed.
Solution 1:
Attach a NOCLIP, KEEP, or S attribute to the affected pad net
(the 3 properties are equivalent) to prevent the pushing of the
zero to the input of the INFF.
This problem is fixed in the M1.3 release.
Reference No.: 17489
End of Record #2457 - Last Modified: 10/07/97 21:58 |
