Research 200 MHz HyperRAM for R4/R5 boards

[sy2002]

Looks like the newer HyperRAM chips on R4/R5 boards are able to cope with 200 MHz instead of the 100 MHz we are currently using. Would be a very welcome latency reduction and speed boost.

[MJoergen]

In the HyperRAM repository I've created a branch "mfj_175MHz". Link: https://github.com/MJoergen/HyperRAM/tree/mfj_175MHz

[MJoergen]

I'm not sure where this idea about a 200 MHz HyperRAM came from (maybe me?), and I think it's false.

The R3 board uses a IS66WVH8M8BLL-100B1LI (https://www.issi.com/WW/pdf/66-67WVH8M8ALL-BLL.pdf) chip (for U29), which indeed is rated to 100 MHz.

However, the R5 board uses a IS66WVH8M8DBLL-100B1LI (https://www.issi.com/WW/pdf/66-67WVH8M8DALL-BLL.pdf) chip (for U29), which is identical except it is "die revision D". Specifically, this chip is also only rated to 100 MHz.

I'm looking specifically at page 46 in the latter document:

[MJoergen]

I'm guessing the confusion arose because the revision D does indeed come in a 200 MHz version (as can be seen above), but the R5/R6 boards only use the 100 MHz version.

[MJoergen]

However, what is confusing me is that section 10.3 of the revision D document above only details timing values for 200 MHz, 166 MHz, and 133 MHz versions. So timing details for the 100 MHz is not even documented!

[sy2002]

@MJoergen Well, then we might want to close this "research" project here - shouldn't we?