LabVIEW FPGA Idea Exchange

Visually detecting the presence of CDC (Clock Domain Crossing) in LV code is only semi-intuitive. It is required to check the set clock of the SCTL and / or follow the wire to the clock constant / control in order to understand in which clock domain the code is running.

I suggest having the option to automatically colour the background of the SCTL according to the clock being used.

Obviously, this won't work well over VI borders, but at least the option to have it vivible on the same diagram is already a nice step towards better visibility of this really important part of LabVIEW FPGA programming.

An option to actually couple a colour with any given clock constant / control for SCTLs would be an addition I personally would very much appreciate.

Yes, these colours are probably a bit extreme, but given the fact that I'm dealing with so many individual processes, it is preferable to having to constantly follow all the wires or investigate all of the SCTL settings.

Hi,

I'd like to request that NI enables the use of Xilinx XPM Macros in Component Level IP (CLIP) and Socketed CLIP and custom user IP:

Xilinx recomments XPM macros for Clock Domain Crossing (CDC) and FIFO / Memory instantiation because they are more easily reconfigured / managed than classical IP and (especially in case of CDCs) auto-generate timing constraints to ease getting a correctly constrained design.

XPM Macros are available for all current Xilinx/AMD devices (7-Series to Versal):

XPM Macros in 7-Series Libraries:

https://docs.amd.com/r/2021.1-English/ug953-vivado-7series-libraries/Xilinx-Parameterized-Macros 

XPM Macros in UltraScale Libraries:

https://docs.amd.com/r/en-US/ug974-vivado-ultrascale-libraries/Xilinx-Parameterized-Macros 

XPM Macros in Versal (Premium/AI) Libraries:

https://docs.amd.com/r/en-US/ug1344-versal-architecture-libraries/Xilinx-Parameterized-Macros 

https://docs.amd.com/r/en-US/ug1485-versal-architecture-premium-series-libraries/Xilinx-Parameterized-Macros 

https://docs.amd.com/r/en-US/ug1353-versal-architecture-ai-libraries/Xilinx-Parameterized-Macros 

Unfortunately, XPM macros are only available in SystemVerilog at lowest level, although VHDL instantiation templates do exist (see documentation above).

AMD/Xilinx seems to have no plans to add pure VHDL XPM Macros:

https://support.xilinx.com/s/question/0D52E00006hpeAySAI/no-vhdl-simulation-models-for-xpms-?language=en_US 

Excerpt:

graces (AMD) on 2017-12-07
There's no plan to support VHDL model for XPM in future releases.

graces (AMD) on 2017-12-14

The Xilinx direction for any new development is in Verilog. It can be overridden with business justification though.

If you have a strong demand, I'd suggest that you open a Service Request with Technical Support and get a CR filed. The SR will be linked to the CR. If quite a few SRs are linked to the CR, the chance to get it implemented will be larger.

Since NI does not document that the FPGA module does not play nicely with CLIP that uses XPM macros, I had to find out what is needed to get them to work:

My preliminary result is that I can get a bit file if I only change/patch the call of xelab that the FPGA module performs from

xelab.bat -m64 xil_defaultlib.conf12B308D38326465793B06F85282B8708 -L xil_defaultlib -L unisim -L unimacro -L xilinxcorelib -L secureip -snapshot my_clip_top_level_entity -dll -prj clipsyn.prj

to 

xelab.bat -m64 xil_defaultlib.conf12B308D38326465793B06F85282B8708 -L xil_defaultlib -L unisim -L unimacro -L xilinxcorelib -L secureip -L xpm -snapshot my_clip_top_level_entity xil_defaultlib.glbl -dll -prj clipsyn.prj

and add the line 

verilog xil_defaultlib "C:\NIFPGA\programs\Vivado2021_1\data\verilog\src\glbl.v"

to clipsyn.prj.

I'm using Labview 2022Q3 with the 2022Q3 FPGA module, targeting a sbRIO-9629's Artix 7 with the bundled Vivado 2021.1

So it seems all that is needed to enable the use of XPM macros in (socketed) CLIP is a configuration option that performs a simple extension of the elaboration command arguments and file list.

If NI decides not to support XPM macros for whatever reason, this should be documented very prominently in the CLIP sections of the user manuals. Also, NI should consider providing their own macros with the same functionality in this case, at least for CDCs.

Using a netlist or user IP to wrap XPM CDC macros does not work, since the design constraints are added by tcl files (partially only as exceptions), that are not retained in the netlist or IP, see

https://support.xilinx.com/s/question/0D54U00008aHc9ESAS/handleretainexport-xpm-cdc-macro-timing-constraints-for-ooc-design-exported-to-a-netlist-that-is-then-used-and-implemented-with-another-design?language=en_US 

So there is currently no workaround to use a design that depends on them.

Thanks for considering this.

It would be nice to have control of clock.-independent assignments of signals from I/O nodes (without synchronising registers) without having to specifically having to use a clock for the connection.

Image says it all.

We have tried using a static assignment on the top-level diagram, without using a SCTL but it appears that does not work. The example links within a single CLIP, but the idea is aimed at actually doing some connections between multiple different CLIPs without the need for a specific VHDL wrapper for each individual configuration.