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FPGA design engineer and blogger, placing particular emphasis on test and formal verification

Jun 23, 2021, 12 tweets

Vivado 2021.1 is now available! It's a whopping 51GB download. But is it worth it?

Let's go check if they've fixed any of the bugs that've been around since 2018, shall we?

Let's start with their AXI-lite slave template, the one you get via "Create and Package New IP" ...

No, that's still broken--it still drops requests in the presence of any back pressure. (It's been doing this since at least 2016, if not 2014 or before.)

How about their AXI full slave template?

No ... that's still broken, it doesn't latch the AxID signals and so risks sending responses to the wrong master. I reported this back in May of 2019.

What about their AXI stream master template? How hard can AXI stream be?

No ... that one will still set TLAST if the penultimate beat ever stalls.

What about their production IP? Surely the bugs in their own IP have been fixed by now, no?

Well, no, apparently not. The bug above in their AXI Ethernet Lite IP will guarantee that the wrong RDATA gets returned when reading from the core if the master hasn't (yet) raised RREADY.

Their AXI Quad SPI controller remains broken as well. If you hit it with a read and a write request on the same clock, it will process the read request using AWLEN and not ARLEN. (This one hasn't been reported ...)

So this leaves me wondering ... if they haven't fixed the bugs in the prior versions, what assurances do you have that this brand new 51GB version, and all of the brand new features found within it, will be bug free? Or that any bugs, if found, will ever get fixed?

The sad thing is that many of these bugs were reported years ago. Support requests have been submitted, and tickets have been created. Now, years later, they're still shipping broken IP.

I'll let you draw your own conclusions.

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