I have a Simulink design which requires quite a large word lenght (64bit signed fixed-point) to run without overflows.
Now I want to optimize my design by using the Fixed-point Tool Add-On in order to identify the required resolution of sub-blocks in my design.
However, I get a strange error when I try to collect the ranges.
The block "select" is inside the "Simple dual-port RAM" block and is locked, i.e. cannot be edited. The signal "Idx1", which is connected to the "rd_addr" port, is driven by a unsigned integer (unsigned fixed-point number with no fraction). By monitoring this signal I can confirm that no signal with the value "-16" enters the RAM block. Therefore, I do not know what causes this error. Unfortunately, the RAM block is locked and I cannot monitor the internal signals.
I attached a simple Simulink model which reproduces the problem.
How can I fix this?