The implementation was causing regressions on actual designs, rework done:
- Only keep a common iteration loop as before.
- Add iteration on CLKO dividers (to fall in the VCO range).
- Do the iterations as before, if while doing it we find a clock suitable for feedback: just use it.
- If no feedback clock has been found: create it (if at least one free output available, if not raise an error).
- Shift in _csr_rd_buf should only been done when buf is set.
- When CSR size is not an exact multiple of the CSR data-width, the gap is in
the low addresses, not the high ones. So offset is introduced to take this into
account.
Dynamically adjusting the phase of a feedback will cause it to unlock.
The phase adjust ports are shared by all the outputs, so there is no
technical way to prevent this. Allow the user to indicate that they
will not adjust a clock when requesting an output by setting
uses_dpa=False, and only consider those that the user has promised not
to use.
Reimplement the configuration loop to allow all 4 outputs to be used by
the user, if one of them is suitable for use as VCO feedback.
The new strategy is to first iterate over requested outputs to see if
any of them can be used as a feedback source. If one can, it is
selected, and if no output is suitable, it attempts to instantiate one.
Once the feedback path is selected, the VCO frequency is known and it
attempts to calculate the remaining outputs' settings.
In addition, this implementation now respects datasheet limits in two
new ways:
- It respects the post-input-divider minimum frequency of 10MHz
- It respects the max output frequency of 400MHz for instantiated
feedback outputs
I am slightly unhappy with the seemingly-repetitive for loops. However
each one has slightly different sematics and I don't see a way to
combine them that doesn't hinder readability.
**Problems**
On macOS USB CDC ACM, which appears as `/dev/tty.usbmodem*`,
somehow `lxterm` keeps failing to send a payload.
**Solution**
Increase delay.
It's very unknown why to me, however, probably macOS USB CDC ACM
driver implementation issue.
**Testing**
Tested on MacBook Air (2020, M1) for OrangeCrab (rev.0.2) target
with Linux on LiteX SoC bitstream build from current commit and
load prebuild Linux On LiteX image.
Florent Kermarrec
Jędrzej Boczar
Christian Klarhorst
Gwenhael Goavec-Merou
Joey Bushagour
George Hilliard
Yoshimasa Niwa
Ilia Sergachev
Vadzim Dambrouski
developandplay