- reduced frame fanout, removed clock gater in erx_io (improves speed path)
- driving constants on "wid signals" (proper)
- making lock signal 1 bit wide to remove warning
- moved backed to BUFIO for IDDR blocks
- Using the BUFIO makes another clock domain....FPGAs apparently hate clock domain crossings, avoid them at all cost.
- Now moving back to having on high speed clock domain for logic and DDR blocks, take care of IO alignment in software for TX and RX
- Also, fixed the io_wait path with logic...not sure what I was thinking there. Logic was trivial. The way it was,the io path was going straight into the FIFO as a wait.
- Giving a wait on every ack just doesn't make sense on the read port with a fifo there??
- Makes for a nasty combinatorial loop during integration.
- Test passes (but need to look into this more)
- Using new packet interface
- Adding active signal, indicating that link is ready. This way you don't need to guess when the link is ready (no magic constants)
- Removed register on por reset input to get rid of x on startup.
- reset was broken!
- need to account for wait
- merging read/write wait for simplicity, otherwise you would need to reset the packets to figure out if it's a read or write transaction...and I don't want to reset every packet throughout the pipe.
- holding rx in reset state until tx is done
- removing reset from all pipeline registers
- removing reset from oddr/iddr
- the idea is to keep things quiet not to block in lots of places. The only real block needed is in the FIFO to keep "noise" from propagating past the link. The link should be kept in a safe reset state until the rx fram is stable and the clock is running so that the pipe can be cleaned out.
- 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!
-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?
