[fpga] ChipWhisperer CW310 follow-up tasks

[vogelpi]

6614 adds initial support for the ChipWhisperer CW310 board with Xilinx Kintex 7 XC7K410T FPGA. When doing the PR and during the review process, a couple of follow-up items got identified:

Tooling:

• ~[ ] Investigate adding support for SPI Flashing over SAM3X/U to sw/host/spiflash, see https://github.com/lowRISC/opentitan/pull/6614#discussion_r637067566~ This could theoretically be done but we dropped support for NexysVideo and kept using cw310_loader.py for the ChipWhisperer boards. In the meantime, opentitantool is used for bootstrapping FPGA. Once opentitantool has the ability to also prep VMEM images for bootstrapping in DV sim, spiflash might get removed. See https://github.com/lowRISC/opentitan/pull/12821#issuecomment-1135453310
• ~[ ] Investigate adding support for bitstream flashing over SAM3X/U to opentitan-pgm-fpga~ This could theoretically be done by leveraging the FTDI MPSEE interface emulation of the SAM3X/U. However, there are some restrictions on what FPGA pins can be made available to the FTDI MPSEE interface by default. Some of them can be dynamically switched through Python. See https://github.com/lowRISC/opentitan/pull/12633#discussion_r879539230 for details. In the end, we didn't have a strong need for this so far and kept using cw310_loader.py instead. In the meantime, we dropped support for NexysVideo and opentitan-pgm-fpga got removed with #12821.
• [x] Investigate reducing additional Python dependencies such as numpy, scipy introduced through the ChipWhisperer Python API, see https://github.com/lowRISC/opentitan/pull/6614#issuecomment-844323063 , see #12832
• [x] Investigate installing the ChipWhisperer Python API not in editable mode
• [x] #8739

Hardware:

• [x] Enable SCA support: need to feed target clock, high-precision trigger signal and UART to the scope board via 20-pin ChipWhisperer connector, see #7513
• [x] Disable the use of hw/top_earlgrey/util/top_earlgrey_reduce.py. See lowRISC/OpenTitan#7369
• [x] Decide on the future of NexysVideo support.
• ~[ ] Enable support for the smaller ChipWhisperer CW310 board with Xilinx Kintex 7 XC7K160T FPGA?~ We are not going to do this for now as it's not clear whether supporting yet another, non-complete FPGA configuration is really worth the effort. We keep supporting the CW305 as we already have quite a few boards of that sort and there is a benefit in terms of noise for power SCA.

[colinoflynn]

On reducing numpy and scipy:

I think numpy gets used for some binary list conversion in the CW310 board interface would be the only hit. SciPy should be avoidable. It's listed as a dependency for ChipWhisperer as it will break some of the SCA algorithms, which for most users is important. Longer-term we could add a separate 'chipwhisperer-api' or similar module release which is built from the same code-base but removes the dependency, or if the CW310 API is stable the relevant files could be moved to OT (we have the copyright so this can be done cleanly w/o messing up the copyright notices).

[imphil]

Longer-term we could add a separate 'chipwhisperer-api' or similar module release which is built from the same code-base but removes the dependency

Having a reduced package that only contains the "connectivity" parts would be fantastic; the existing "chipwhisperer" package could then depend on that to avoid duplicating the code. (And since we want it, we're also willing to invest time into helping with the implementation, of course.)

Having a dependency on Python packages in OpenTitan is fine, we don't need to vendor everything in. However, we try to keep the dependency tree reasonably small to avoid a "support nightmare". We have, for example, users on RHEL6 that routinely have trouble building binaries, including C extensions of some Python packages. The large majority of OpenTitan developers only wants to flash an FPGA and load a bit of software, but doesn't need the full power of the ChipWhisperer platform.

[a-will]

Closing, as all tasks have been completed.