Altera ALTERA_MULT_ADD Saturation

[shaiko]

Hello,

Has anyone ever configured the ALTERA_MULT_ADD core to use Saturation and Rounding ?

 

[FvM]

Saturation is a DSP hardware feature of some FPGA families, e.g. Stratix II - IV. It can be only used in mult_add IP if the hardware supports it.

 

[shaiko]

Saturation is a DSP hardware feature of some FPGA families, e.g. Stratix II - IV. It can be only used in mult_add IP if the hardware supports it.

So if I'm using Arria V for example - I'll have to do it with logic ?

 

[FvM]

Yes. ieee.fixed_pkg saturation and rounding features can be e.g. used.

 

[shaiko]

is ieee.fixed_pkg well supported for synthesis ?

 

[TrickyDicky]

is ieee.fixed_pkg well supported for synthesis ?

Depends on tool, version, etc.
I think only synopsys supports the 2008 version. Other tool support the '93 compatible version (that you will need your own copy of).

Otherwise rounding and saturation is a simple operation.
Round = +0.5 and chop the LSBs off.
Saturate is just some compares and a mux.

 

[shaiko]

Otherwise rounding and saturation is a simple operation.
Round = +0.5 and chop the LSBs off.
Saturate is just some compares and a mux.

Simple as it is - it'll almost certainly be slower than the speed of the hardened DSP silicon.
A weak link in the chain.

The more I look at it the more it seems like Xilinx's DSP48 is richer than Altera's block (at least for Arria & Cyclone devices).

 

[FvM]

Otherwise rounding and saturation is a simple operation.
Round = +0.5 and chop the LSBs off.
Saturate is just some compares and a mux.

Yes, you can write functions to perform the operations. The convenience of fixed_pkg is that is is redefining the arithmetic operators. Altera Quartus has ieee.fixed_pkg supported with VHDL 2008 since version 15.