DSP Double Pumping

[tde_m]

Following an old question (https://forums.intel.com/s/question/0D50P00004MInzpSAD/double-pumping-dsp-units-ip) is there any way to allow double pumping of DSPs in Stratix 10 and to exploit this directly in OpenCL?

Thanks

[HRZ]

The OpenCL compiler does not support DSP double-pumping and in fact, even Block RAM double-pumping that was supported for older FPGAs (Stratix V and Arria 10) has been disabled for Stratix 10. Even though this would be a very useful feature since kernels on Stratix 10 tend to run at far lower frequencies than the promised 800-900 MHz, seeing how even the existing Block RAM double-pumping was disabled for Stratix 10, I would not expect DSP double-pumping to ever be supported. The option to implement DSP double-pumping manually in RTL and using it as an RTL blackbox in OpenCL theoretically exists, but it won't be easy to implement and I am not sure if the OpenCL compiler provides a 2x clock on Stratix 10 anymore (or at all).

[Kenny_Tan]

Let me get engineering to look into this for S10. Since feature can increase the Fmax.

[Kenny_Tan]

Double pumping does work on S10. You can apply the attribute doublepump to request double pumping for a given array.  Will request to have it on dsp for the future. Thanks

[tde_m]

Thanks!

In your opinion, would it be possible to implement it as RTL block? Does OpenCL compiler/designs provide everything that I would need for that?

I could not find any useful documentation for this.

Thanks

[HRZ]

@KennyT_Intel​ This is not true, Section 10.3 of the documentation (https://www.intel.com/content/www/us/en/programmable/documentation/mwh1391807516407.html#jhl1520273455239) clearly states that no 2x clock is provided in the design by the compiler for Stratix 10 and hence, Block RAM double-pumping is not available on Stratix 10. This also means that any type of double-pumping cannot be implemented by the user in RTL either since there is no 2x clock in the system generated by the compiler.

[Kenny_Tan]

Thanks for pointing out, the attribute doublepump for Startix 10 should be working. The compiler may not infer double-pumping my default, but the attribute should always be able to override that. 

Will have this documentation corrected.

[HRZ]

Interesting; I just tested Block RAM double-pumping on Stratix 10 and indeed it seems to work. All this time I was thinking it won't work because the documentation said so. Having DSP double-pumping on top of that will be extremely valuable and a huge advantage over the main competitor's HLS compiler (among numerous other advantages that Intel's HLS compiler has). In fact, on Stratix 10 there is probably room to even do triple-pumping, considering how high the peak operating frequency of the Block RAMs and the DSPs is compared to typical kernel frequency.

[Kenny_Tan]

You can refer to https://www.intel.com/content/www/us/en/programmable/documentation/mwh1391807516407.html#chn1469549457114__section_or3_mk2_5w -> Double Pumping

You will find an example there.

[tde_m]

Thanks, but my question was related to DSP Double Pumping, not to BRAM Double Pumping. The Intel documentation mention only the latter.

[Kenny_Tan]

As of now, we do not have DSP double pumping, I had make a request for the engineering to have it in the future. Thanks