- more modular
- two bits cominng from sys_clk elink config domain
- drives the tx and rx from top level elink
- from software you would probably write 2'b11 to reset both at same time
- Making all resets async since we cannot guarantee that we have a clock coming in from RX. This is needed due to the way we use a PLL for alignment. If we would have used a free running local clock this would have been different, but this would have required a FIFO for synchronization betwen the rx and rxdiv4 clock.
- Moving the clock block into the RX for modularity
- Making a specil rx soft reset (driven from sys_clk domain)
- Still there is a POR_reset so the link should wake up ok
- This is DEFINITELY the way to do things, sweep the delays and find the right value. No f'ing way to get these stupid FPGAs to work otherwise with the ridiculuosly over margined PVT nubmers they are running through the STAs. I understand they want to make the design bullet proof, but as a result designers are wasting countless hours overoptimzinng designs and being clever. So much performance is left on the table for expert users.
- Lesson: I/O design should be "self syncrhonizing". Only contraints in the design should be create_clk
- Made RX clock async, too tricky to guarantee that there clock is there. No way to do this if the clock sources are actually independent for RX/TX!
- As a dirty a model hack as they come, using positive and negative edge of CLKIN to sample the signal and phase align the clock output.
- Will only work with div 2/4/8 etc
- There may be other issues, have to think about it...
- But the test now passes cleanly and the clocks look good.
-apparantly the MMCM needs a reset after the clock changes
-need to hold reset high until we know that there is an active clock on input
-doesn't it make more sense to use idelay?
-Set VCO_MULT to 1 for PLL. Dirty hack to allow the RX clk to phase align with the input. Otherwise, if you multiply the VCO clock and then divide, you get a random phase alignment the way the current clock divider is written.
-Changed the fifo_cdc to 32 entries. Forgot that I had changed the fifo_cdc to hard coded per number of entries. Really need to have a parametrixed model that works!!
