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91f8e3db5a
- After finding the bug in the reference model and wasting countless hours going back and forth with FPGA timing optimization and bug tweaks, I realized that the design was fundementally broken. The decision to use two clock domains (high speed) and low speed was correct from the beginning. The FPGA is dreadfully slow, (you definitely don't want to do much logic at 300MHz...), but the handoff between tclk and tclk_div4 was too complicated. The puzzle of having to respond to wait quickly, covering the corner cases, and meeting timing was just too ugly. - The "new" design goes back to the method of using the high speed logic only for doing a "dumb" parallel to serial converter and preparing all the necessary signals in the low speed domain. - This feel A LOT cleaner and the it already passes basic tests with the chip reference and the loopback after less than 3 hours of redesign work! - The TX meets timing but there is still some work to do with wait pushback testing.