- Bypass path was ugly! Always try to go through the same logic path as much as possible.
- Note: when MMU is enabled, you need to put in entry for read return (ie 810)
- Gating mailbox_not empty with irq_en. bit [28] of RXCFG
- Changing elink output interrupt to "or" of not_empty and full
- Adding mailbox status register (mostly for debug)
- Moving register addresses to make space for mailbox status register
- Fixing wrappers for DV
- Updating README docs with new register map
- Removing mailbox from RX status reg. Doesn't belong there, should be coupled with mailbox for modularity.
- Turns out I was debugging ghosts for ~1 day today. Everything was working in simulation but nothing works in the FPGA. Since I was only changing small logic stuff, I didn't bother checking the warning messages in Viviado. Turns out for some reason it was throwing away some logic and disconnecting all the important rr signals
- This is where I was making changes, but I still can't figure out what exactly was happening...doesn't make sense. Either there is a bug in icarus or in vivado, this shouldn't happen!
- 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.
- Turns out I had a nasty bug that was masked by using my own RX to loopback the TX. Since the new RX is very benign with a programmable fifo full flag the timing is quite relaxed.
- The legacy elink for e16 has a strict wait policy. When wait is raised high, you must stop pretty much immediately.
- I struggled with testing this bug on the parallella for 2 days.
- Putting together the test environment uncovered the bug in a couple of hours. F**K, I should know better!!
