xc7 MMCM support

[mkurc-ant]

This pull requests adds support for MMCM block for Xilinx 7-series devices.

The supported features are:

• Basic (integer) multiplier and divider control,
• Fractional multiplier (CLKFBOUT) and divider (CLKOUT0) support,
• Duty cycle control,
• Phase shift control,
• Bandwidth and compensation settings,
• Local control input inverters (CLKINSEL, PSEN, PSINCDEC, PWRDWN, RST)
• Startup wait enable/disable

Dynamic phase shift and dynamic reconfiguration are supported as well.

All the remaining MMCM functionality is not supported at the moment mostly due to missing bitstream documentation. This is tracked in f4pga/prjxray#1473

This PR also adds tests/examples for MMCM which are available under xc/xc7/tests/mmcm and can be run on hardware (some of them).

[mkurc-ant]

While disassembling Vivado bitstreams of MMCM designs I'm consistently getting these two unknown bits:

{ unknown_bit = "0040151c_30_19", unknown_segment = "0x00401500", unknown_segbit = "28_979" }
{ unknown_bit = "0040151c_31_28", unknown_segment = "0x00401500", unknown_segbit = "28_1020" }

[litghost]

While disassembling Vivado bitstreams of MMCM designs I'm consistently getting these two unknown bits:

{ unknown_bit = "0040151c_30_19", unknown_segment = "0x00401500", unknown_segbit = "28_979" }
{ unknown_bit = "0040151c_31_28", unknown_segment = "0x00401500", unknown_segbit = "28_1020" }

This doesn't surprise me too much. I disabled the compension features because they were initially causing me trouble, see here: https://github.com/SymbiFlow/prjxray/blob/91d91357b5077b12e578ac741322bea71c285b6a/fuzzers/031-cmt-mmcm/generate.py#L128-L131

Now that the basic MMCM features and pips are in, maybe it is time to go back and get the compension features working?

GitHub

SymbiFlow/prjxray

Documenting the Xilinx 7-series bit-stream format. - SymbiFlow/prjxray

[mkurc-ant]

@litghost I've checked and currently the MMCM does not work in hardware when using SymbiFlow bitstream. It looks like the two unknown bits I mentioned before are required for it to work. I've tested Vivado and SymbiFlow bitstreams for the same design where the only difference between them was the latter missing these two bits. The Vivado bitstream works while the SymbiFlow doesn't.

[mkurc-ant]

This one solves the two missing bits: f4pga/prjxray#1491

[litghost]

This equivalent site is wrong?

[mkurc-ant]

Fixed.

[litghost]

@mkurc-ant Can you please rebase this PR?

[mkurc-ant]

@litghost Done. I'm now working on adding MMCM support to fasm2bels.

[litghost]

Latest error:

CMake Error at xc/xc7/tests/mmcm/CMakeLists.txt:46 (add_dependencies):
  The dependency target "mmcm_random_case3_vivado_diff_fasm" of target
  "all_xc7_mmcm_vivado_diff_fasm" does not exist.