Answers Database

M1/ Synplicity: MAP gives "ERROR:x4kma-Unable to obey design constraints"


Record #2413

Product Family:  Software

Product Line:  Merged Core

Problem Title:
M1/ Synplicity:	MAP gives "ERROR:x4kma-Unable to obey design
constraints"



Problem Description:
Keywords: map, synplicity

Urgency: standard

General Description:

A Synplicity design may cause MAP to issue an error similiar
to the following:

ERROR:x4kma - Unable to obey design constraints which require
the combination of the following symbols into a single CLB

One known cause of this is that Synplicity will under some
circumstances create buffers for each branch of a high fanout
RESET net. The output of each buffer has a new name
for the net, although logically it is still the same net.

Synplicity will also put "X" flags on the outputs of the
buffers, and this will prevent the buffers from being trimmed
out.

The problem arises because Synplicity also puts BLKNMs and
FMAP symbols on the logic to constrain it into a particular
CLB. Since the reset net is going to both flops in the same
CLB,  MAP will give this error because there are two
different reset nets going to two flops in the same CLB
(illegal; only one asynchronous reset per CLB for the 4000).
MAP cannot reduce the RESET net to a single net
because of the X flags.


Solution 1:

Within Synplicity, you can try to disable "increased
drivers due to high fanout".

Furthermore, if you intend for RESET to go to every flop,
you should use the STARTUP block, rather than
local routing.



End of Record #2413