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enjoy-digital / litedram

Small footprint and configurable DRAM core
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Initialization failed on Artix after e5e3b6c #293

Closed kaolpr closed 2 years ago

kaolpr commented 2 years ago

We've updated LiteX and dependencies lately and it turned out that our Artix-based board started failing on memory (SDRAM) initialization. After some cross checking and building with different commits of litedram we've found that that commit https://github.com/enjoy-digital/litedram/commit/e5e3b6c9a3f9108e2db63ce21f111fe131199878 was the problem.

It seems that write_latency_calibration should always be True for S7 DDR Phy as physical elements that sdram_write_latency_calibration (sdram.c) function interacts with are present regardless of with_odelay parameter.

Setting write_latency_calibration = True in master version of litedram made initialization successful again.

@enjoy-digital Can you please confirm and, if my findings are right, merge https://github.com/enjoy-digital/litedram/pull/294 ?

enjoy-digital commented 2 years ago

Hi @kaolpr,

thanks for the feedback, can you tell me a bit more about the Artix-based board that are failing? Are they off-the-shelf boards or custom ones?

I did https://github.com/enjoy-digital/litedram/commit/e5e3b6c9a3f9108e2db63ce21f111fe131199878 doing the write latency calibration was making calibration fail on some boards (ex Acorn CLE215+). We could also do it a bit differently and allow user to configure this (And enabled by default). This would solves your issue and would allow me to also disable it on the problematic board. But if you are seeing this behavior on an off-the-shelf board (that I maybe also have), I could investigate more.

kaolpr commented 2 years ago

I was using AFC v4.0. There are ~10 units of this revision running in different institutions and we have no information on hardware issues related to SDRAM (though I believe we're using it with LiteX only at Technosystem at the moment).

enjoy-digital commented 2 years ago

Thanks @kaolpr. I just exposed the write_latency_calibration parameter and set it to True by default. This will allow me to disable it on Artix7 boards where it is problematic.

enjoy-digital commented 2 years ago

Exposed and reverted to True by default with https://github.com/enjoy-digital/litedram/commit/e48471ea43c82a473d4b58bda32760b852d776a7.

enjoy-digital commented 2 years ago

@kaolpr: Sadly, enabling write_latency_calibration by default causes issues on others boards than the Acorn (ex Digilent Arty), so I now disabled it by default with https://github.com/enjoy-digital/litedram/commit/4c1ce026e93b6aaf07a4b2734bcf61c68e0160d8. In your target file, you'll then have to add write_latency_calibration=True on the A7DDRPHY.