MULT18X18s Overmapped in FPGA

[C Wang]

I have built a quite large controller using the FPGA module 1.1, LabVIEW 7.1.1, and PXI-7831R. When I build the program using the embeded project manager, I keep getting the Overmapped error from MULT18x18 multiplier. The message look like this (58 out of 40 145% (OVERMAPPED)). From the knowledge base I know that the number of multiplier in FPGA is limited to 40 but I must have 21 pairs of 32 bit multiplication .

I did try to change multiplier to Compound Arithmetic multiplications as suggested in the knowledge base but the number of MULT18X18s are not decrease. What I have done wrong ? Are there any other ways to solve the problem ? I have spare space in other kinds of gates .. only this one gives me problems.

Thanks in advance..

[Arun_V]

Hello Wang,

A 32 bit multiplication takes up 3 multipliers on the FPGA. considering we have only 40 multiplier blocks, we can only do 13 multpilications of 32 bit numbers. The workaround is to use the multipliers as sub VIs. But remember that the sub VI is going to be shared resource and so if you want to have a truly parallel connection then it might not work out. Also when using sub VIs be aware of race conditions too.

Regards,

Arun V
National Instruments

[cortexM]

Dear Aron,

I have the same problem. I need more moltiplication block on my FPGA design on sbrio. How can I implement multiplication as subVi as you suggested?

Mario

[Intaris]

What speed do you need the multiplications to be done at?

What speed does the rest of your code run at?