Document MMCM advanced features

[mkurc-ant]

In its current state (6e3f053) the prjxray database contains documentation for bits controlling the following MMCM features:

• Internal register bank controlling:
  • Multiplier
  • Dividers (both integer and fractional)
  • Phase shifts
  • Duty cycles
  • Clock output enabling
  • Bandwidth settings (via lookup tables)
• Local control input inverters (CLKINSEL, PSEN, PSINCDEC, PWRDWN, RST)
• Compensation settings
• Startup wait
• Dynamic reconfiguration (no bits required)
• Dynamic phase shift (no bits required)

This issue is to track documenting bits controlling the advanced features of MMCM which are:

• Fine grained phase shift
• CLKOUT4 and CLKOUT6 divider cascading
• Spread spectrum clock generation

It is not yet clear how the advanced features are controlled by bitstream. The work neccesary for identifying and documenting bits responsible for those features will require either modifying existing MMCM fuzzer(s) (031-cmt-mmcm for MMCM itself or 034b-cmt-mmcm-pips for MMCM tile PIPs) or creating new one(s).

[mkurc-ant]

Preliminary tests indicate that CLK*_USE_FINE_PS features may correspond to the MX[0] bit of the ClkReg2 register (see XAPP888) of each clock output.

[mkurc-ant]

As of 6e3f053 bits for the parameter enabling/disabling spread spectrum clock (SS_EN) are already known. Other related parameters are not yet documented.