Proposal for clarification of handling of phase of negedge active, don't care duty cycle clocks

Hi,

here is the proposal for how to change the text to clarify how phase
of negedge active, don't caer duty cycle clocks is handled.

On p. 30 of the 1.1.0 spec, Section 5.2.4.1, the section with the
heading `DutyHi=0, DutyLo=100, Phase=0', change last sentence of the
first paragraph which starts `The phase shift is expressed in the
same units' to:

  The phase shift is expressed in the same units; continuing the
  example, if Phase=30, the clock is shifted 30% of its period
  before the first low to high transition occurs.  The phase shift
  normally refers to the low to high transition.  However, for the
  special case of DutyHi greater than 0 and DutyLo equal to 0, i.e.,
  negedge active, don't care duty cycle clocks [add reference to
  section 5.2.4.3 here], the phase shift refers to the high to
  low transition [emphasize high to low].

  NOTE: The reason for the special case for negedge active, don't
  care duty cycle clocks follows from the observation that such
  a clock can be viewed as being high the whole period (since
  DutyHi + DutyLo = DutyHi) and then
  low for a 0-time wide glitch (DutyLo = 0).  That is, the clock
  can be viewed as having a virtual rising edge that occurs at
  the same time as the falling edge.  So stating
  that the phase shift refers to the virtual rising edge of a
  negedge active, don't care duty cycle clock is equivalent to
  stating that the phase shift refers to the falling edge.

The note is the motivation for the special case.  I'd be happy
to consider any proposal to make it clearer and easier to understand.
Or should we just leave it out?  It might be a good idea to
add another figure that shows some different clocks with various
phase shifts or add a couple of negedge active, don't care duty
cycle clocks to Figure 13, one with 0 phase and another with non-0
phase (not 50%, though as that makes it hard to see the sign of
the phase shift).

Per

-- 
Per Bojsen                                Email: <bojsen@zaiqtech.com>
Zaiq Technologies, Inc.                   WWW:   http://www.zaiqtech.com
78 Dragon Ct.                             Tel:   781 721 8229
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